2000-2001 Final Report
ENVIRONMENTAL QUALITY OF WILMINGTON AND
NEW HANOVER COUNTY WATERSHEDS
2000-2001
by
Michael A. Mallin, Lawrence B. Cahoon, Martin H. Posey, Lynn A. Leonard, Douglas C.
Parsons, Virginia L. Johnson, Ellen J. Wambach, Troy D. Alphin, Kim A. Nelson and James F. Merritt
CMS Report 02-01
Center for Marine Science
University of North Carolina at Wilmington Wilmington, N.C. 28409
February, 2002
Funded by:
The City of Wilmington, New Hanover County, and
the North Carolina Clean Water Management Trust Fund
Executive Summary
This report represents combined results of Year 8 of the New Hanover County
Tidal Creeks Project and Year 4 of the Wilmington Watersheds Project. Water quality
data are presented from a watershed perspective, regardless of political boundaries. The combined programs involved 13 watersheds and 65 sampling stations. In this
summary we first present brief water quality overviews for each watershed, and then
discuss key results of several special studies conducted over the past two years.
Barnards Creek – There was a general fecal coliform bacterial pollution problem at all stations sampled throughout the Barnard’s Creek watershed. Lower Barnard’s Creek at
River Road had occasional poor water quality as judged by turbidity and fecal coliform
counts, although dissolved oxygen at this station showed improvement over last year.
Incoming and outflowing water at the wet detention pond on Echo Farms Golf course
were sampled, with orthophosphate, total phosphorus, conductivity and pH all significantly higher in the stream exiting the course. Other nutrients were somewhat
higher in waters exiting the course than in the inflowing waters. However, the
concentrations of those nutrients were low in comparison to other area golf courses
sampled, possibly because of nutrient uptake in a natural wetland through which the
outfall stream passes before leaving the course.
Bradley Creek – Turbidity was not problematic during 2000-2001, except occasionally in
the upper south branch of the creek. Low dissolved oxygen was an occasional problem
in brackish waters of the creek during late spring and summer. Elevated nitrogen and
phosphorus levels enter the creek in both the north and south branches, and two algal blooms occurred in the south branch during 2000-2001. Fecal coliform bacteria were
sampled only at the station at College Acres, which proved to be contaminated on 83%
of the occasions sampled.
Burnt Mill Creek – A sampling station on Burnt Mill Creek at Princess Place had substandard dissolved oxygen during 33% of the sampling trips. This station also had
poor microbiological water quality, exceeding the standard for human contact in seven
of 12 samples, and hosted two algal blooms in 2001. The effectiveness of Ann
McCrary wet detention pond on Randall Parkway as a pollution control device
decreased from last year. The pond led to significant reduction only in conductivity, while it led to a significant increase in nitrate loading to the creek. Because of the
design there is short-circuiting of the pond from a large tributary near the pond outfall.
Further, all water quality parameters indicated a subsequent worsening of the creek
from where it exited the pond to the downstream Princess Place sampling station.
Fecal coliform bacteria and low dissolved oxygen are the primary problems in Burnt Mill Creek.
Futch Creek – Futch Creek maintained good microbiological water quality, as it has
since channel dredging at the mouth occurred in 1995 and 1996. Algal blooms and
turbidity were not problems in 2000-2001. Periodic low summer dissolved oxygen concentrations occurred creekwide, as have occurred in previous years. This creek
continues to display some of the best water quality in the New Hanover County tidal
creek system, due to generally low development and impervious surface coverage in its watershed.
Greenfield Lake – The three tributaries of Greenfield Lake (near Lake Branch Drive,
Jumping Run Branch, and Lakeshore Commons Apartments) all suffered from low
dissolved oxygen problems on numerous occasions, as did station GL-2340, within the lake proper. All three of the tributaries also had frequent high fecal coliform counts, and
maintained geometric mean counts in excess of the state standard for human contact
waters. The stream near Lakeshore Commons also maintained high nitrate and
phosphate concentrations. The lake again experienced algal blooms at times, with two
blooms exceeding 100 µg/L of chlorophyll a at the park, and two blooms exceeding 60
µg/l at the Lakeshore Commons station. Generally, nutrient loading was highest at a
station (GL-2340) located in the south end that receives several urban and suburban
inputs. Fecal coliform bacterial contamination was prevalent at all in-lake and tributary
stations during 2000-2001, as was the case in 1999-2000. A large regional wet detention pond on the tributary Silver Stream did a very
good job of reducing pollutant loads to the lake from this drainage. Statistically
significant reductions in ammonium, nitrate, total nitrogen, orthophosphate, total
phosphorus, conductivity, and fecal coliform bacteria were all realized. The design of
this pond consists of two interconnected basins containing large amounts of diverse aquatic vegetation, with most inputs directed into the upper basin. This could serve as
a potential model for future large pond design.
During this period the UNCW Aquatic Ecology Laboratory conducted a weekly
waterfowl survey around Greenfield Lake. The results of this study showed that
waterfowl distribution was not spatially correlated with nutrient and fecal coliform concentrations at the various lake locations. However, the study also showed that
waterfowl, principally cormorants, can contribute as much as 27% of the annual
phosphorus load to Greenfield Lake. Waterfowl appeared to contribute a very small
amount of the nitrogen load to this lake, however. An analysis of rainfall vs nutrients
showed a strong correlation between rain events and nitrate loading into the lake, particularly in the upper lake areas nearest the tributaries. Thus, it appears that
waterfowl contribute a significant amount of phosphorus to the lake, whereas nitrate
enters from the surrounding watershed during rain events to encourage algal bloom
formation. The analysis also showed that chlorophyll a was strongly correlated to
biochemical oxygen demand (BOD), indicating the algal bloom decay may be largely
responsible for BOD loading within the lake. The analysis also showed that rainfall was correlated with fecal coliform counts in the upper lake, showing inputs from the
watershed during runoff. The waterfowl do not appear to be the major contributors of
fecal coliforms; possibly dogs and cats around the lake and in the areas drained by
tributaries are the major sources of this human health pollutant.
Hewletts Creek – This creek received high nutrient loading in its three upper branches,
with several minor algal blooms occurring in the south branch near Pine Grove Road.
The middle branch had the highest nutrient concentrations, largely derived from two golf
courses. Low dissolved oxygen occurred periodically in the north and south branches,
and the middle creek sites. All three tributary stations and the upper main section of the creek exceeded the safety standard for human contact water on several occasions
each. The two stations closest to the ICW (HC-M and HC-2) had generally clean water microbiologically.
Howe Creek – Three stations were sampled in Howe Creek in 2000-2001. The creek
maintained generally good water quality. Algal bloom problems were not found,
turbidity was generally low, and low dissolved oxygen was not problematic last year. Fecal coliform bacteria were not sampled during 2000-2001.
Motts Creek – This creek was sampled at only one station, at River Road. One algal
bloom occurred during this period, and low dissolved oxygen was a problem 25% of the
sampling occasions in 2000-2001. Turbidity and suspended sediments were a periodic problem and fecal coliform pollution a frequent problem at this station.
Pages Creek – This creek maintained generally good water quality during 2000-2001.
Nutrient loading and phytoplankton growth was low, even at the most
anthropogenically-impacted stations. However, there was periodic hypoxia in warmer months, particularly at some stations draining Bayshore Drive. Lower Pages Creek
maintained excellent microbiological water quality for shellfishing and the upper creek
was always well within standards for human contact. This watershed has some of the
lowest development and impervious surface coverage in the New Hanover County tidal
creek system.
Smith Creek – Smith Creek had moderate water quality problems as reflected by
several parameters. Turbidity and elevated suspended sediments occurred on
occasion, and algal blooms exceeding 30 µg/L of chlorophyll a occurred twice at one
station. Fecal coliform bacterial counts exceeded the state standard for human contact waters at both sampling sites on a number of occasions. Low dissolved oxygen
problems occurred 25% of the time at our Smith Creek stations during 2000-2001.
Whiskey Creek – Whiskey Creek had relatively high nutrient loading but generally low
chlorophyll a concentrations in 2000-2001. There were several incidents of low dissolved oxygen at four of the five stations sampled this year, and high turbidity occurred periodically at one site. Fecal coliform bacteria were not sampled in 2000-
2001 in this creek.
Upper and Lower Cape Fear Watersheds – Water quality at the one station on the stream draining the Upper Cape Fear watershed (behind the Wilmington police station) had high nitrate concentrations, although they were lower than in previous years. Fecal
coliform concentrations often exceeded the state standard for human contact waters at
this station, and on occasion at the station draining Greenfield Lake during 2000-2001.
Algal blooms and turbidity from Greenfield Lake were also sometimes transported to the Cape Fear River through this station.
Little Creek – By request of concerned citizens, Little Creek was sampled on four
occasions in 2001. Turbidity, nutrients, and chlorophyll a were all low. Fecal coliform
bacterial counts were usually low but one incident of 200 CFU/100 mL occurred at the
station nearest the ICW in July, possible due to a release from a boat. Significant land runoff of pollutants was not detected by our sampling in 2001.
Use Support Ratings – The NC Division of Water Quality utilizes an EPA-based system
to help determine if a water body supports its designated use (described in Appendix
B). We applied these standards to the water bodies described in this report, based on
2000-2001 data. Our analysis shows that (based on fecal coliform standards for human
contact waters) all of upper Barnards Creek was non-supporting while lower Barnard’s Creek is partially supporting. Three of the four stations in Burnt Mill Creek were non-
supporting in 2000-2001, and the other was partially supporting. Futch Creek was fully
supporting for fecal coliform bacteria, including for shellfishing throughout the lower
creek. Pages Creek was fully supporting for human contact throughout and for
shellfishing in the lower creek. Greenfield Lake and its tributaries were non-supporting throughout. Hewletts Creek was non-supporting at five of eight stations sampled.
Lower Motts Creek was non-supporting and both of the Smith Creek stations were
partially supporting. The Upper Cape Fear station was non-supporting and the Lower
Cape Fear station was partially supporting. We also list support categories for
chlorophyll a, dissolved oxygen and turbidity in Appendix B.
Non-point source runoff of pollutants is a major problem in coastal communities,
including New Hanover County. Thus, we conducted a study examining the interaction
of phosphorus, a major pollutant subject to runoff, and soils, which bind readily with
phosphorus. The data demonstrated that phosphorus content of soils depended
strongly on land use. Soils under suburban and golf course grasses was highest in phosphorus, followed by soils in wet detention ponds and runoff channels, with soils in
undisturbed forests having the least phosphorus associated with them. This indicates
that phosphorus is running off of fertilized landscapes and making its way to coastal
waters. As further evidence, phosphorus in New Hanover County tidal creeks peaked
in 1996 when fertilizer shipments into the county were highest. The results suggest that the public fertilizer user groups need more education on judicious application of
fertilizers and land use practices (i.e. buffer zones and other best management
practices) that help retain fertilizers in targeted areas without allowing excess runoff into
water resources.
During the past year we have analyzed several structural and ecological features
of oyster reefs in four of the tidal creeks. The results of this continuing project suggest
considerable variability in oyster reef characteristics among the various New Hanover
tidal creeks examined. Pages Creek was distinguished by high shell coverage,
relatively high densities of live oysters (compared to other creeks examined), and intermediate vertical relief. The reefs in this creek have a generally well-developed
physical structure and appear to support significant oyster densities. Though reefs may
cover a large percent of the overall area of Whiskey Creek (ongoing analyses), these
reefs are poorly developed with respect to physical structure and support low densities
of live oysters. The Whiskey Creek oyster reefs may reflect stress from disease, siltation, or other factors affecting survival and growth of oysters. Howe and Hewletts
Creeks exhibit intermediate patterns. Howe Creek has intermediate shell cover within
reefs and high vertical relief, but low live oyster density within reefs. This may reflect
recent mortality or low recruitment set combined with persistence of shells from dead
individuals. Hewletts Creek had relatively high live oyster densities, but low relief. This suggests that most oysters are smaller (size measurements are planned for an
upcoming survey) or reefs have a flatter profile due to disturbance, harvesting, or tideflat topography. Our goals over the coming year, as we finish analysis of
morphology and coverage, will be to evaluate how the different functions of oyster reefs
(habitat, water quality, larval sources, and human use) effect and are affected by these
characteristics. By combining planned experimental studies with assessment of natural
reef patterns, we hope to eventually develop an understanding of how oysters may differentially affect communities in the various tidal creek systems.
Over the past two years the Program has conducted a pilot project investigating
the use of constructed oyster reefs as water quality improvement tools. This work has
demonstrated that small viable oyster reefs can be established and maintained over periods of at least one year in small upland tidal creek feeder channels; regions most
likely to first feel the effects of contaminant loading from adjacent uplands. Further,
these results suggest that an optimal ratio of reef size to flow discharge exists whereby
the filtration benefits provided by oyster reefs is a maximum. Additional studies are
needed to determine the volume to reef ratio and the reef geometry that would achieve desired results utilizing minimum resources. This study concludes that placement of a
small Crassostrea virginica reef at this site resulted in increased flow velocity over the
reef, reduced total suspended solids concentrations except during periods of elevated
load, and decreased chlorophyll a concentration below the reef after increasing the size
of the reef.
Table of Contents
1.0 Introduction 1
1.1 Methods 1
2.0 Barnards Creek 3
3.0 Bradley Creek 6 4.0 Burnt Mill Creek 9
5.0 Futch Creek 12
6.0A Greenfield Lake 15
6.0B Waterfowl and Rainfall Effects on Greenfield Lake Nutrients 20
7.0 Hewletts Creek 35 8.0 Howe Creek 39
9.0 Motts Creek 41
10.0 Pages Creek 44
11.0 Smith Creek 47
12.0 Upper and Lower Cape Fear 50 13.0 Whiskey Creek 52
14.0 Little Creek 55
15.0 Soil phosphorus, Land use, and Phosphorus Loading to New Hanover
County Tidal Creeks 57
16.0 Studies of Oyster Reefs in New Hanover County Tidal Creeks 67 17.0 Use of Installed Oyster Reefs to Improve Water Quality 78
18.0 References Cited 93
19.0 Acknowledgments 95
20.0 Appendix A: Selected N.C. water quality standards 96
21.0 Appendix B: Water Body Use Support Rankings Based on DWQ Chemical Standards 97
22.0 Appendix C: GPS coordinates for the New Hanover County Tidal Creek
and Wilmington Watersheds Program sampling stations 99
23.0 Appendix D: UNCW reports related to tidal creeks 101
(Cover by Scott Ensign)
1.0 Introduction
Since 1993, scientists at the UNC Wilmington Center for Marine Science
Research have been studying five tidal creeks in New Hanover County. This project,
funded by New Hanover County, the Northeast New Hanover Conservancy, and
UNCW, yielded a comprehensive report detailing important findings from 1993-1997, and produced a set of management recommendations for improving creek water quality
(Mallin et al. 1998a).
Additionally, in October 1997 the Center for Marine Science Research began a
project (funded by the City of Wilmington Engineering Department) with the goal of assessing water quality in Wilmington City watersheds under base flow conditions.
Additionally, certain sites were analyzed for sediment heavy metals concentrations
(EPA Priority Pollutants). In the past three years we have produced combined Tidal
Creeks – Wilmington City Watersheds reports (Mallin et al. 1998b; 1999; 2000a). In the
present report we present results of continuing studies from 2000-2001 in the tidal creek complex and the City of Wilmington watersheds.
The water quality data within is presented from a watershed perspective. Some
of the watersheds cross political boundaries (i.e. parts of the same watershed may lie in
the County but not the City). Bradley and Hewletts Creeks are examples. Water quality parameters analyzed in the tidal creeks include water temperature, pH, dissolved
oxygen, salinity/conductivity, turbidity, nitrate, ammonium, orthophosphate, chlorophyll
a, and in selected creeks fecal coliform bacteria. Similar analyses were carried out in
the City watersheds with the addition of total Kjeldahl nitrogen, total nitrogen (TN), total
phosphorus (TP), and suspended solids. In 1999-2000 Whiskey Creek was added to
the matrix of watersheds analyzed by our combined programs.
1.1 Methods
Field parameters were measured at each site using a YSI 6920 Multiparameter
Water Quality Probe (sonde) linked to a YSI 610 display unit. Individual probes within the instruments measured water temperature, pH, dissolved oxygen, turbidity, salinity,
and conductivity. YSI Model 85 and 55 dissolved oxygen meters were also used on
occasion. The instruments were calibrated prior to each sampling trip to ensure
accurate measurements.
For the six tidal creeks, water samples were collected monthly, at or near high
tide. For nitrate+nitrite (hereafter referred to as nitrate) and orthophosphate
assessment, three replicate acid-washed 125 mL bottles were placed ca. 10 cm below
the surface, filled, capped, and stored on ice until processing. In the laboratory the
triplicate samples were filtered simultaneously through 1.0 micrometer pore-sized glass fiber filters using a manifold with three funnels. The pooled filtrate was stored frozen
until analysis. Nitrate+nitrite and orthophosphate were analyzed using a Technicon
AutoAnalyzer following EPA protocols. Samples for ammonium were collected in
duplicate, field-preserved with phenol, stored on ice, and analyzed in the laboratory
according to the methods of Parsons et al. (1984). Fecal coliform samples were collected by filling pre-autoclaved containers ca. 10 cm below the surface, facing into
the stream. Samples were stored on ice until processing (< 6 hr). Fecal coliform concentrations were determined using a membrane filtration (mFC) method (APHA
1995). North Carolina water quality standards relevant to this report are listed in
Appendix A.
The analytical method used to measure chlorophyll a is described in
Welschmeyer (1994) and US EPA (1997). Chlorophyll a concentrations were determined from the 1.0 micrometer glass fiber filters used for filtering samples for
nitrate+nitrite and orthophosphate analyses. All filters were wrapped individually in
aluminum foil, placed in an airtight container and stored in a freezer. During the
analytical process, the glass filters were separately immersed in 10 ml of a 90%
acetone solution, and ground using a teflon grinder. The acetone was allowed to extract the chlorophyll from the material for two hours, after which the material was
centrifuged, leaving the solution containing the extracted chlorophyll. Each solution
was then analyzed for chlorophyll a concentration using a Turner AU-10 fluorometer.
This method uses an optimal combination of excitation and emission bandwidths that
reduces the errors inherent in the acidification technique.
Samples were collected monthly within the Wilmington City watersheds from
August 2000 through July 2001. Field measurements were taken as indicated above.
Nutrients (nitrate, ammonium, total Kjeldahl nitrogen (TKN), total nitrogen (TN),
orthophosphate, and total phosphorus (TP)) and total suspended solids (TSS) were
analyzed by a state-certified contract laboratory using EPA and APHA techniques. We also computed inorganic nitrogen to phosphorus molar ratios for relevant sites (N/P).
Chlorophyll a was run at UNCW-CMS as described above.
For three detention ponds (Ann McCrary Pond on Burnt Mill Creek, Silver Stream
Pond in the Greenfield Lake watershed, and the main pond on Echo Farms Golf Course in the Barnards Creek watershed) we were able to obtain data from input (control) and outfall stations. We used these data to test for statistically significant differences in
pollutant concentrations between pond input and output stations. The data were first
tested for normality using the Shapiro-Wilk test. Normally distributed data parameters
were tested using the paired-difference t-test, and non-normally distributed data parameters were tested using the Wilcoxon Signed Rank test. Statistical analyses were conducted using SAS (Schlotzhauer and Littell 1987).
2.0 Barnards Creek
The water quality of lower Barnard’s Creek is becoming an important issue as a
major housing development is commencing construction activities in the area east of
River Road and between Barnard’s and Mott’s Creeks. We report collected data at a
station located on Barnard’s Creek at River Road (BNC-RR) that drains part of this area. The BNC-TR site in Barnard’s Creek watershed drains a wooded area and had
been considered a control site for nutrients and physical parameters. However, we also
note that the control is now near an active road and condominium construction area on
Titanium Road, or Independence Road Extension (Fig. 2.1). Fecal coliform bacterial
counts at BNC-TR have increased considerably relative to the 1997-1998 period (Mallin et al. 1998b; 1999). The BNC-CB site is near Carolina Beach Road and drains an area
hosting construction activities. BNC-TR and BNC-CB both exceeded the state fecal
coliform standard seven of 12 samples (Table 2.1; Appendix B). All of the sites in the
Barnard’s Creek watershed were significantly impaired by elevated fecal coliform
counts during 2000-2001.
The Barnard’s Creek watershed hosts the Echo Farms Country Club. Much of
the course drainage enters a large (1.75 acre) pond, which discharges through a
wooded wetland. We sampled a pond input station draining a suburban area (BNC-EF)
and the pond outflow exiting the riparian wetland (BNC-AW). A primary goal was to assess the efficacy of golf course nutrient removal by this pond during the period
August 2000 – July 2001. Golf course loading led to significant increases in
orthophosphate and TP, among nutrients (Table 2.2), whereas last year increases were
seen only in orthophosphate. There were input-output increases in conductivity, as well
(Table 2.2). We also point out that overall concentrations of inorganic nutrients in the output stream were low in comparison with output from other area golf courses (Mallin
and Wheeler 2000). The design of a wet detention pond followed by a natural wetland
area does a good job of keeping nutrient concentrations low in the course outfall.
We report here water quality data from the estuarine site on River Road. BNC-RR had average salinity of 4.9 ppt with a range of 0.3-13.7 ppt. Lower Barnard’s Creek
had dissolved oxygen levels below 5 mg/L on only one occasion out of 12 samples in
2000-2001. The results of six BOD5 tests in 2001 yielded a median of 1.0 and a mean
of 0.8 mg/L. Turbidity on average was moderately high (22 NTU), and exceeded the
state standard for estuarine waters of 25 NTU three times, which was an improvement from last year. Fecal coliform counts exceeded the state standard two of 12 occasions
for a 17% non-compliance rate. Thus, this station can be considered somewhat
impaired by turbidity and fecal coliform loading.
Table 2.1. Mean and standard deviation of water quality parameters in Barnard’s Creek watershed, August 2000-July 2001. Fecal coliforms as geometric mean; N/P ratio as
median.
_____________________________________________________________________
Parameter BNC-TR BNC-CB BNC-RR
_____________________________________________________________________
DO (mg/L) 6.8 (1.3) 7.3 (1.4) 6.8 (1.8)
Turbidity (NTU) 3 (1) 9 (7) 22 (11)
TSS (mg/L) 5.9 (3.7) 6.0 (6.3) 20.9 (10.2)
Nitrate (mg/L) 0.075 (0.058) 0.056 (0.041) 0.156 (0.106) Ammon. (mg/L) 0.013 (0.011) 0.031 (0.021) 0.018 (0.012)
TN (mg/L) 0.661 (0.713) 0.573 (0.552) 0.763 (0.578)
Phosphate (mg/L) 0.027 (0.014) 0.024 (0.015) 0.079 (0.038)
TP (mg/L) 0.066 (0.051) 0.074 (0.067) 0.135 (0.044)
N/P molar ratio 7.6 11.6 4.3
Chlor. a (µg/L) 1.1 (1.1) 1.0 (0.6) 6.7 (7.9)
Fec. col.(/100 mL) 257 272 100
_____________________________________________________________________
Table 2.2 Mean and standard deviation of water quality parameters in Barnard’s Creek watershed, including a comparison of pollutant concentrations in input (BNC-EF) and
output (BNC-AW) waters of wet detention pond on Echo Farms Country Club, August
2000-July 2001.
_____________________________________________________________________
Parameter BNC-EF BNC-AW _____________________________________________________________________
DO (mg/L) 5.7 (1.2) 6.2 (1.5)*
Cond. (µS/cm) 139 (26) 221 (63)**
pH 6.9 (0.4) 7.1 (0.3)** Turbidity (NTU) 2 (1) 2 (1)
TSS (mg/L) 4.0 (3.0) 6.7 (5.8)
Nitrate (mg/L) 0.047 (0.077) 0.083 (0.150)
Ammon. (mg/L) 0.027 (0.025) 0.033 (0.041)
TN (mg/L) 0.528 (0.672) 0.602 (0.772) Phosphate (mg/L) 0.028 (0.011) 0.045 (0.019)**
TP (mg/L) 0.063 (0.053) 0.084 (0.044)**
N/P molar ratio 3.5 3.4
Chlor. a (µg/L) 2.8 (4.7) 3.3 (6.4)
Fec. col.(/100 mL) 130 168 _____________________________________________________________________
* Indicates significant difference between input and output concentration at p<0.05
**Indicates significant difference between input and output concentration at p<0.01
3.0 Bradley Creek
The Bradley Creek watershed is of particular current interest as a principal
location for Clean Water Trust Fund mitigation activities, including the purchase and
renovation of Airlie Gardens by the County. This creek is one of the most polluted in
New Hanover County, particularly by fecal coliform bacteria (Mallin et al. 2000b). Seven stations were sampled in the past year, both fresh and brackish (Fig. 3.1).
As with last year, turbidity was not a problem during 2000-2001 (Table 3.1). The
standard of 25 NTU was exceeded twice at BC-SBU and once each at BC-SB and BC-
NBU (Table 3.1). There were some problems with low dissolved oxygen (hypoxia), with BC-76 and BC-NB both having DO of less than 5.0 mg/L on three occasions and BC-
CA had substandard dissolved oxygen conditions on two of 12 sampling occasions
(Appendix B). Only one station was sampled for fecal coliform concentrations last year
(BC-CA – the creek as it passes beneath College Acres). This station had a geometric
mean concentration of 614 CFU/100 mL, with a range of 10 – 4,900. Fecal coliforms exceeded the state human contact standard of 200 CFU/100 mL on ten of 12
occasions, a 83% non-compliance rate (Appendix B).
Table 3.1 Parameter concentrations at Bradley Creek sampling stations, 2000-2001.
Data as mean (SD) / range. _____________________________________________________________________
Station Salinity (ppt) Turbidity (NTU) Dissolved Oxygen (mg/L)
_____________________________________________________________________
BC-76 32.2 (2.4) 3 (2) 6.9 (1.9) 27.3-34.5 1-8 4.2-9.7
BC-SB 15.4 (11.4) 10 (10) 7.0 (1.1)
0.2-31.0 3-35 5.3-8.7
BC-SBU 0.1 (0.0) 7 (10) 7.7 (1.9)
0.1-0.2 1-29 4.5-12.6
BC-NB 23.0 (11.8) 6 (4) 6.6 (2.0)
0.1-33.4 2-13 3.5-9.6
BC-NBU 0.1 (0.2) 9 (11) 7.6 (0.6)
0.1-1.9 3-41 6.9-9.1
BC-CR 0.1 (0.0) 2 (7) 7.4 (0.6) 0.0-0.1 0-24 6.3-8.9
BC-CA 0.1 (0.1) 7 (8) 5.8 (1.3)
0.1-0.2 3-25 2.8-7.9
_____________________________________________________________________
Nitrate concentrations were highest at stations BC-CR (draining a suburban residential area along Clear Run Drive), BC-SBU (upper south branch) and BC-CA
(draining apartment complexes, construction areas, and retail establishments
upstream). Particularly high orthophosphate levels were found at BC-CA, with
somewhat elevated orthophosphate levels at BC-SB, BC-SBU, and BC-NB (Table 3.2).
Ammonium was also elevated at BC-CA. Bradley Creek hosted two algal blooms in
excess of the state standard of 40 µg/L, both at BC-SB (Table 3.2). Median inorganic
molar N/P ratios were 7.5 for BC-76, 12.3 for BC-SB, and 9.8 for BC-NB. This indicates
that phytoplankton growth was likely nitrogen limited at all three of these stations.
Table 3.2. Nutrient and chlorophyll a data at Bradley Creek sampling stations, 2000-
2001. Data as mean (SD) / range, nutrients in mg/L, chlorophyll a as µg/L.
_____________________________________________________________________
Station Nitrate Ammonium Orthophosphate Chlorophyll a
_____________________________________________________________________
BC-76 0.004 (0.002) 0.020 (0.014) 0.006 (0.003) 1.6 (1.2)
0.001-0.007 0.002-0.044 0.001-0.013 0.3-3.9
BC-SB 0.046 (0.069) 0.026 (0.033) 0.011 (0.010) 12.9 (16.7)
0.004-0.244 0.003-0.119 0.003-0.040 0.5-45.9
BC-SBU 0.107 (0.056) NA 0.012 (0.015) 5.4 (6.0)
0.011-0.203 0.003-0.059 0.5-16.1
BC-NB 0.025 (0.039) 0.023 (0.021) 0.012 (0.017) 4.5 (6.5) 0.002-0.144 0.001-0.065 0.002-0.064 0.4-21.0
BC-NBU 0.100 (0.051) NA 0.003 (0.003) 0.9 (0.8)
0.001-0.195 0.001-0.011 0.1-2.6
BC-CR 0.251 (0.079) NA 0.009 (0.009) 0.8 (0.6)
0.057-0.396 0.001-0.035 0.1-1.9
BC-CA 0.074 (0.057) 0.051 (0.027) 0.034 (0.016) 7.1 (13.9)
0.005-0.190 0.005-0.100 0.010-0.070 0.6-50.0 _____________________________________________________________________
4.0 Burnt Mill Creek
The Burnt Mill Creek watershed was sampled just upstream of Ann McCrary
Pond on Randall Parkway (AP1), along shore at mid-pond (AP2), about 40 m
downstream of the pond outfall (AP3), and in the creek from the bridge at Princess
Place (BMC-PP - Fig. 4.1). Ann McCrary Pond is a large (28.8 acres) regional wet detention pond draining 1,785 acres, with an apartment complex at the upper end near
AP1. The pond itself usually maintains a thick growth of submersed aquatic vegetation,
particularly Hydrilla verticillata, Egeria densa, Alternanthera philoxeroides,
Ceratophyllum demersum and Valliseneria americana. A survey in late summer 1998
indicated that approximately 70% of the pond area was vegetated. There have been
efforts to control this growth, including addition of triploid grass carp as grazers. Our survey also found that this pond is host to Lilaeopsis carolinensis, which is a threatened
plant species in North Carolina.
Turbidity and suspended solids concentrations were low to moderate. Fecal
coliform concentrations entering Ann McCrary Pond at AP1 were very high, however
(Table 4.1), possibly a result of pet waste runoff from the apartment complex and runoff from urban upstream areas. Nine out of 12 samples at AP1 had counts exceeding 200
CFU/100 mL. A July 2001 algal bloom showed chlorophyll a concentrations of 149, 70,
and 89 µg/L at AP2, AP3, and Princess Place, respectively. Additionally, there was a
bloom of 54 µg/L chlorophyll a at Princess Place in May. The efficiency of the pond as a pollutant removal device was poor last year.
Fecal coliforms were reduced during passage through the pond, although this was not a
statistically significant reduction (Table 4.1). Total suspended solids and turbidity were
low entering the pond this year and there was no significant difference in removal of these two parameters. There were no statistically significant decreases in nutrients during passage through the pond this year, and nitrate was actually significantly
increased through pond passage (Table 4.1). As in previous years, it is likely that
inputs of nutrients have entered the pond from a suburban drainage stream midway
down the pond across from our AP2 site. Also, intensive waterfowl use of the pond, particularly at a tributary near the outfall, may have contributed to nutrient loading in the pond and along its shoreline. There was a significant decrease in conductivity through
the pond. Dissolved oxygen significantly increased through the pond, probably
because of in-pond photosynthesis and aeration by passage over the final dam at the
outfall. There was a significant increase in pH as well, probably due to utilization of CO2 during photosynthesis in the pond.
The Princess Place location experienced some water quality problems during the
sample period (Appendix B). Dissolved oxygen was substandard on four of 12
sampling trips, for a non-compliance rate of 33%. The most important issue, from a public health perspective, was the excessive fecal coliform counts, which maintained a geometric mean (328 CFU/100 mL) well in excess of the state standard for human
contact waters (200 CFU/100 mL). Fecal coliform counts were greater than 200
CFU/100 mL in seven of 12 samples, or 58% of the time. It is notable that fecal
coliform, phosphorus and nitrogen concentrations all increased considerably along the
passage from BMC-AP3 to the Princess Place location, while dissolved oxygen decreased (Table 4.1).
The UNCW Aquatic Ecology Lab has conducted additional fecal coliform and
BOD sampling at various locations along Burnt Mill Creek. Preliminary data show
elevated pollutant concentrations entering the stream from urban sources in the headwaters near Kerr Avenue and from a tributary stream entering the creek from an
apartment complex between AP3 and Princess Place. Burnt Mill Creek has been
targeted for restoration by the North Carolina Wetlands Restoration Program, and
UNCW began additional sampling of multiple parameters with funding from this group in
summer 2001.
Table 4.1. Mean and (standard deviation) of water quality parameters in Burnt Mill
Creek watershed, 2000-2001. Fecal coliforms given as geometric mean; N/P ratio as
median.
_____________________________________________________________________ Parameter BMC-AP1 BMC-AP2 BMC-AP3 BMC-PP
_____________________________________________________________________
DO (mg/L) 5.7 (1.3) 8.8 (2.5) 9.8 (1.3)** 6.0 (1.7)
Cond. (µS/cm) 249 (57) 222 (64) 218 (59)* 343 (117) pH 6.6 (0.4) 7.1 (0.7) 7.4 (0.7)** 7.1 (0.4)
Turbidity (NTU) 18 (43) 9 (13) 6(7) 9 (7)
TSS (mg/L) 11.5 (21.8) 6.9 (7.5) 5.5 (4.7) 9.1 (4.6)
Nitrate (mg/L) 0.069 (0.053) 0.121 (0.133) 0.142 (0.203)* 0.231 (0.161)
Ammonium (mg/L) 0.068 (0.141) 0.038 (0.039) 0.034 (0.034) 0.030 (0.017) TN (mg/L) 0.617 (0.336) 0.618 (0.559) 0.490 (0.335) 0.733 (0.615)
Phosphate (mg/L) 0.041 (0.042) 0.026 (0.023) 0.022 (0.016) 0.044 (0.030)
TP (mg/L) 0.084 (0.061) 0.086 (0.070) 0.088 (0.090) 0.207 (0.291)
N/P molar ratio 10.7 15.8 23.3 15.4
Fec. col. (/100 mL) 392 165 121 328
Chlor. a (µg/L) 4.5 (4.4) 17.7 (41.5) 10.7 (18.9) 14.8 (27.6)
_____________________________________________________________________
* Indicates statistically significant difference between AP1 and AP3 at p<0.05
**Indicates statistically significant difference between AP1 and AP3 at p<0.01
5.0 Futch Creek
During 1995 and 1996 two channels were dredged in the mouth of Futch Creek
(Fig. 5.1) to improve circulation and hopefully reduce fecal coliform bacterial
concentrations. There was a statistically significant increase in salinity in the creek in
the months following dredging, significantly lower fecal coliform counts, and the lower creek was reopened to shellfishing (Mallin et al. 2000c). In 1999-2000 two stations, FC-
2 and FC-20, were dropped from the sampling scheme. During 2000-2001, none of the
creek stations had turbidity levels exceeding the state standard of 25 NTU on any
occasion. However, low dissolved oxygen was a problem at Futch Creek during the
past year, with FC-13, FC-17 and FOY each having substandard dissolved oxygen on five occasions (Appendix B).
Table 5.1. Physical parameters at Futch Creek sampling stations, 2000-2001. Data
given as mean (SD) / range.
_____________________________________________________________________ Station Salinity (ppt) Turbidity (NTU) Dissolved oxygen (mg/L)
_____________________________________________________________________
FC-4 33.4 (2.2) 5 (3) 7.4 (1.9)
28.2-36.5 1-10 4.9-9.7
FC-6 32.2 (2.7) 6 (3) 7.4 (2.0)
25.7-36.5 2-12 4.7-9.9
FC-8 30.8 (3.7) 8 (5) 6.9 (2.2) 24.0-36.1 2-17 3.9-10.0
FC-13 25.9 (6.1) 9 (6) 6.7 (2.5)
15.3-34.7 2-20 3.3-10.4
FC-17 20.2 (10.7) 8 (5) 6.0 (2.4)
1.2-33.8 2-17 2.8-9.7
FOY 24.7 (7.6) 6 (3) 7.3 (2.5)
10.8-34.8 2-9 3.7-10.7 _____________________________________________________________________
Nutrient concentrations in Futch Creek were generally low, with the exception of
periodic nitrate pulses in the upper station FC-17 (Table 5.2). The source of these
pulses has been identified as groundwater inputs entering the marsh in springs in the area upstream of FC-17 downstream to FC-13 (Mallin et al. 1998b). The creek was
free from algal blooms during our sampling visits (Table 5.2), even in the upper stations.
Computed median inorganic N/P molar ratios were 13.1 for FC-4, 13.4 for FC-17 and
17.8 for FOY, all indicating neither strong N nor P limitation of phytoplankton growth.
N/P expressed no particular seasonality over the year.
Table 5.2. Nutrient and chlorophyll a data at Futch Creek sampling stations, 2000-
2001. Data as mean (SD) / range, nutrients in mg/L, chlorophyll a as µg/L.
_____________________________________________________________________
Station Nitrate Ammonium Orthophosphate Chlorophyll a
_____________________________________________________________________
FC-4 0.008 (0.006) 0.028 (0.012) 0.007 (0.003) 1.3 (1.1) 0.002-0.020 0.015-0.055 0.003-0.011 0.3-3.6
FC-6 0.013 (0.011) NA 0.007 (0.003) 1.4 (1.1)
0.003-0.035 0.003-0.012 0.4-3.4
FC-8 0.016 (0.011) NA 0.008 (0.003) 1.8 (1.3)
0.004-0.041 0.004-0.014 0.4-3.9
FC-13 0.024 (0.014) NA 0.010 (0.004) 3.3 (3.7)
0.005-0.052 0.005-0.017 0.3-13.7
FC-17 0.040 (0.028) 0.030 (0.011) 0.012 (0.004) 2.7 (2.3)
0.006-0.087 0.014-0.044 0.006-0.019 0.2-7.0
FOY 0.024 (0.020) 0.027 (0.013) 0.008 (0.004) 2.4 (2.5) 0.005-0.074 0.008-0.047 0.004-0.015 0.2-8.7
_____________________________________________________________________
As reportedly previously (Mallin et al. 2000c) the dredging experiment proved to
be successful and the lower portion of the creek was reopened to shellfishing. During 2000-2001 the lower creek maintained excellent microbiological water quality for
shellfishing (Table 5.3). The mid-creek areas had good microbiological water quality as
well, although geometric mean fecal concentrations increased somewhat compared
with the previous years (Mallin et al. 1999; 2000a). The uppermost stations continued
to have fecal coliform bacterial concentrations well below those of the pre-dredging period. All stations had fecal coliform concentrations that were well within safe limits
for human contact waters (Appendix B).
Table 5.3. Futch Creek fecal coliform bacteria data, including percent of samples
exceeding 43 CFU per 100 mL, 2000-2001. _____________________________________________________________________
Station FC-4 FC-6 FC-8 FC-13 FC-17 FOY ALL
Geomean 2 4 9 26 46 23 20
% > 43 /100ml 0 0 9 42 40 36 36
_____________________________________________________________________
6.0A Greenfield Lake Water Quality
One of the major pollution mitigation features in the Greenfield Lake watershed
is an extensive wet detention pond along the Silver Stream branch (Fig. 6.1). The pond
drains approximately 280.5 acres, of which about 43% is impervious surface area. The
pond is divided into a 1.25 acre upper and a 1.48 acre lower basin by a causeway pierced by three pipes connecting the flow. In early summer 1998 approximately 70%
of the upper pond was covered by a mixture of floating and emergent aquatic
macrophyte vegetation, with about 40% of the lower pond covered by vegetation.
Principal species in the upper basin were alligatorweed Alternanthera philoxeroides,
pennywort Hydrocotyle umbellate, water primrose Ludwigia leptocarpa and cattail
Typha latifolia, while the lower basin vegetation was dominated by alligatorweed, water
primrose, and cattail. This pond functioned very well as a nutrient removal system (Table 6.1). Statistically significant removal of fecal coliform bacteria (78%), nitrate
(72%), orthophosphate (67%), TP (45%), ammonium (39%), and TN (34%) was
achieved. Turbidity and TSS were generally low at both locations this past year, and
there was no change in passage through the pond (Table 6.1). Dissolved oxygen
significantly increased, probably in part because of aeration while passing through the outfall and increased oxygenation through pond photosynthesis. Pollutant removal
efficiencies were as good or better than last year (Mallin et al. 1999).
Table 6.1. Comparison of pollutant concentrations in input (SS1) and output (SS2)
waters of regional wet detention pond on Silver Stream, in Greenfield Lake watershed, August 2000 – July 2001.
_____________________________________________________________________
Parameter SS1 SS2
_____________________________________________________________________
DO (mg/L) 5.1 (1.2) 7.4 (1.8)**
Cond. (µS/cm) 253 (73) 177 (39)**
pH 6.8 (0.2) 6.9 (0.3)* Turbidity (NTU) 6 (11) 5 (5)
TSS (mg/L) 6.0 (4.1) 4.6 (2.5)
Nitrate (mg/L) 0.294 (0.209) 0.081 (0.090)**
Ammonium (mg/L) 0.056 (0.036) 0.034 (0.026)*
TN (mg/L) 0.817 (0.431) 0.542 (0.398)** Phosphate (mg/L) 0.129 (0.055) 0.043 (0.026)**
TP (mg/L) 0.243 (0.106) 0.133 (0.107)**
Chlorophyll a (µg/L) 4.5 (5.4) 9.2 (12.6)
Fecal col. (CFU/100 mL) 551 120*
_____________________________________________________________________ * indicates significant difference between input and output concentration at p<0.05
**Indicates significant difference between input and output concentration at p<0.01
Three tributaries of Greenfield Lake were sampled for physical, chemical, and
biological parameters (Table 6.2, Fig. 6.1). Two of the tributaries suffered from extreme hypoxia, with both GL-LB (creek at Lake Branch Drive) and GL-LC (creek beside
Lakeview Commons) showing average concentrations below the state standard (DO < 5.0 mg/L). Dissolved oxygen levels were substandard seven of 12 times at GL-JRB, 10
of 12 times at GL-LC, and nine of 12 times at GL-LB (Appendix B). Biochemical
oxygen demand (BOD5) was sampled during a series of special projects from October
2000 to July 2001 this past year. Median values were 1.4 mg/L at GL-LB and GL-LC,
and 1.6 mg/L at GL-JRB. The highest mean (1.8 mg/L) and peak (5.0 mg/L) values were at GL-LC in the same months that featured algal blooms (May and June).
Turbidity and suspended solids were generally low in the tributary stations (Table 6.2).
Nitrate concentrations were highest at GL-LC, moderate at GL-JRB and lowest at GL-
LB (Table 6.2). Ammonium concentrations were generally similar across the three
tributary stations. Orthophosphate concentrations were similar at GL-LB and GL-LC, and somewhat lower at GL-JRB. Overall, GL-LC maintained the highest nutrient
concentrations of any of the input streams tested. All three of these input streams
maintained fecal coliform levels indicative of poor water quality, with fecal coliform
counts exceeding the state standard for human contact waters (200 CFU/100 mL) 11 of
12 times at GL-LB, 11 of 12 times at GL-LC, and seven of 12 times at GL-JRB. Chlorophyll a levels were generally low in these streams, with the exceptions of two
algal blooms in GL-LC (Table 6.2).
Table 6.2. Mean and (standard deviation) of water quality parameters in tributary
stations of Greenfield Lake, 2000-2001. Fecal coliforms as geometric mean; N/P ratio
as median. _____________________________________________________________________
Parameter GL-JRB GL-LB GL-LC
_____________________________________________________________________
DO (mg/L) 5.2 (2.5) 2.4 (1.5) 4.4 (1.5)
Turbidity (NTU) 12.7 (25.7) 7.2 (7.1) 3.3 (2.6) TSS (mg/L) 5.1 (2.6) 4.0 (2.1) 2.0 (1.8)
Nitrate (mg/L) 0.203 (0.192) 0.170 (0.187) 0.368 (0.365)
Ammonium (mg/L) 0.085 (0.075) 0.094 (0.059) 0.098 (0.136)
TN (mg/L) 0.707 (0.568) 0.862 (0.725) 0.808 (0.616)
Phosphate (mg/L) 0.033 (0.016) 0.047 (0.012) 0.043 (0.031) TP (mg/L) 0.115 (0.138) 0.103 (0.047) 0.228 (0.435)
N/P molar ratio 21.9 10.5 19.0
Fec. col. (/100 mL) 336 581 457
Chlor. a (µg/L) 3.6 (2.2) 3.7 (3.3) 4.5 (8.8) BOD5 (mg/L) 1.5 (0.5) 1.5 (0.6) 1.8 (1.6) _____________________________________________________________________
Three in-lake stations were sampled (Table 6.3). Station GL-2340 represents an
area receiving a considerable influx of urban/suburban runoff, GL-YD is downstream and receives some outside impacts, and GL-P is at Greenfield Lake Park, away from inflowing streams but in a high-use waterfowl area (Fig. 6.1; Chapter 6.0B). Low
dissolved oxygen affected GL-2340, with 42% of the samples below the state standard
(Appendix B). Median BOD5 was highest at GL-P (3.4 mg/L) followed by GL-2340 (1.9
mg/L) and GL-YD (1.2 mg/L). Mean (4.4 mg/L) and peak (9.0 mg/L) BOD5 levels were also found at GL-P. Highest BOD values were found the same months as when algal blooms occurred in-lake, and algal biomass and BOD were strongly correlated (see
Chapter 6.0B). Turbidity and suspended solids were moderate at the three sites, with highest values during the algal blooms. Fecal coliform concentrations were as bad as
last year, and problematic at all three stations. The annual geometric mean exceeded
the state standard at both GL-2340 and GL-P (Table 6.3). At GL-2340 the state
standard was exceeded on eight of 12 occasions, at GL-YD it was exceeded on three of
11 occasions, and at GL-P it was exceeded on eight of 12 occasions in 2000-2001.
Nitrate concentrations were highest at GL-2340, reflecting the proximity of three
tributary streams. Nitrate levels decreased considerably toward the park (Table 6.3).
Total nitrogen, ammonium, and orthophosphate at GL-P were higher than or
approximately equal to concentrations at the other lake stations (Table 6.3). Inorganic N/P molar ratios can be computed from ammonium, nitrate, and orthophosphate data
and can help determine what the potential limiting nutrient can be in a water body.
Ratios well below 16 (the Redfield ratio) can indicate potential nitrogen limitation, and
ratios well above 16 can indicate potential phosphorus limitation (Hecky and Kilham
1988). Based on the median N/P ratios (Table 6.3), phytoplankton growth in Greenfield Lake should be primarily nitrogen-limited. Our previous bioassay work indicated that
this was indeed the case (Mallin et al. 1999).
Phytoplankton blooms are periodically problematic in Greenfield Lake, and
usually consist of green or blue-green algal species, or both together. These blooms have occurred during all seasons, but are primarily a problem in spring and summer. In
2000-2001 an extensive blue-green algal bloom consisting of Anabaena cylindrica
occurred in May and June 2001, with chlorophyll a ranging from 27 – 169 µg/L at
Stations GL-YD and GL-P. Another bloom occurred in October 2000 at GL-2340 with
chlorophyll a concentrations reaching 70 µg/L. As a reference, chlorophyll a
concentrations of 40 µg/L are considered by the State to be indicative of algal-impaired
waters (NCDWQ 1996). Thus, Greenfield Lake proper is impaired by high fecal
coliform counts, algal blooms, and high sediment metals levels (Mallin et al. 1999); its
tributary stations are impaired by high fecal coliform counts and low dissolved oxygen. The lake in general and its tributaries was in poorer shape in 2000-2001 as compared with 1999-2000.
Table 6.3. Mean and (standard deviation) of water quality parameters in Greenfield Lake sampling stations, 2000-2001. Fecal coliforms given as geometric mean, N/P
ratio as median.
_____________________________________________________________________
Parameter GL-2340 GL-YD GL-P
_____________________________________________________________________ DO (mg/L) 7.0 (1.7) 8.3 (2.8) 8.9 (2.9)
Turbidity (NTU) 5.8 (5.5) 11.1 (15.3) 7.8 (10.1)
TSS (mg/L) 4.4 (2.7) 7.3 (8.8) 7.3 (6.9)
Nitrate (mg/L) 0.179 (0.181) 0.153 (0.201) 0.100 (0.084)
Ammonium (mg/L) 0.039 (0.030) 0.056 (0.041) 0.123 (0.309) TN (mg/L) 0.706 (0.400) 0.959 (0.907) 1.422 (2.323)
Phosphate (mg/L) 0.031 (0.029) 0.036 (0.032) 0.038 (0.030)
TP (mg/L) 0.101 (0.129) 0.110 (0.114) 0.093 (0.077)
N/P molar ratio 13.3 18.2 9.6
Fec. col. (/100 mL) 460 117 279
Chlor. a (µg/L) 7.2 (11.3) 22.7 (36.3) 19.7 (34.8)
BOD5 (mg/L) 2.0 (1.2) 1.2 (0.4) 4.4 (3.0)
____________________________________________________________________
6.0B Effect of Waterfowl and Rainfall on Nitrogen, Phosphorus, and Fecal Coliform
Bacteria in Greenfield Lake
by
Ellen J. Wambach and Michael A. Mallin
Center for Marine Science
University of North Carolina at Wilmington
Wilmington, N.C. 28409
Abstract: Greenfield Lake is located in urban Wilmington, NC and has experienced periods of poor water quality likely resulting from urban runoff and possibly waterfowl
abundance. The purpose of this study was to determine if a direct spatial correlation
existed between waterfowl population density on the lake and phosphorus, nitrogen,
and fecal coliform bacteria. Precipitation was also a factor tested for correlation to
nutrients and bacteria. The waterfowl survey revealed highest waterfowl abundance during the winter months, with cormorants and coots as the most numerous birds.
Waterfowl utilization of Greenfield Lake was not spatially correlated to monthly water
quality parameters. However, precipitation was correlated to total nitrogen and nitrate
concentration, particularly in upper lake areas. Fecal coliform bacteria counts were also
correlated to the 48 and 72 hour sums of rainfall prior to water sampling at an upper lake station. The estimated contribution of total phosphorus by cormorants far
exceeded that of any other bird group and may be significantly contributing to algal
blooms over the long term. Nitrogen contribution by waterfowl to Greenfield Lake
appears to be negligible in comparison with other potential sources.
Introduction
Guanotrophy, nutrient addition by excrement, and its effect on water quality has
been the subject of recent studies (Harris et al. 1981; Gere and Andrikovics 1992; Manny
et al. 1994; Marion et al. 1994; Scherer et al. 1995; Weiskel et al. 1996; Moore et al.
1998; Tobiessen and Wheat 2000). Nutrient input to lakes can significantly increase as a result of guanotrophy (Kear 1963; Manny et al. 1975; Scherer et al. 1995; Moore et al. 1998). Thus, to effectively define a lake’s nutrient budget, waterfowl usage patterns must
be considered. Past studies have indicated increases in phosphorus (Portnoy 1990;
Marion et al. 1994; Scherer et al. 1995; Moore et al. 1998), nitrogen (Portnoy 1990;
Marion et al. 1994), and fecal coliform bacteria (Hussong et al. 1979; Benton et al. 1983;
Weiskel et al. 1996) correlating to waterfowl abundance. For some water bodies, nutrient loading by waterfowl has not significantly affected water quality (Scherer et al. 1995)
especially in proportion to human sewage and agricultural run off (Marion et al. 1994).
However, studies determining the nutrient budget of a lake must consider the effects of
waterfowl populations especially if large numbers of birds feed on land or outside of the
system but excrete into the water.
Greenfield Lake, located in Wilmington, NC, has been studied for water quality
parameters since October 1997 as part of the Wilmington Watersheds Project. The
average depth is approximately 1.2 to 1.5 meters; the surface area is approximately 37
hectares, with a perimeter of close to 28,000 linear feet (D. Mayes, City of Wilmington Stormwater Services, pers. comm.). The lakeshore is developed as Greenfield Park
and receives runoff from the surrounding communities and golf courses. Birds are
attracted to the lake by a plentiful food supply, trees for roosting overnight, and
handouts from humans. Although a wet detention pond (Silver Stream) acts as a
pollution mitigation feature from 113.5 hectares of urban drainage into Greenfield Lake, certain characteristics of the lake are still considered potentially harmful to aquatic life.
For example, from 1998-2000 two of the three tributaries of the lake experienced
extreme hypoxia with average concentrations below the state standard (DO < 5.0 mg/L)
(Mallin et al. 1999; 2000). All three input streams maintained fecal coliform counts
higher than the state standard for human contact waters (200 CFU/100 mL). Already high levels of fecal coliform bacteria found in the tributaries may be worsened in the
lake by seasonal fluctuations in waterfowl abundance. Furthermore, GL-P is an in-lake
station where high waterfowl use was noted; this site showed low turbidity and
suspended solids but high fecal coliform concentrations from 1998-2000. Waste from
numerous waterfowl present near GL-P could contribute to the elevated total nutrients. Concurrent bird counts and nutrient loading per bird use days should provide insight to
the effect of bird abundance on water quality variability among in-lake sites.
Greenfield Lake also experiences problematic phytoplankton blooms periodically
spring through fall. N/P ratios from direct sampling and nutrient addition bioassay experiments indicated phytoplankton growth limitation by nitrogen or nitrogen and
phosphorus combined (Mallin et al. 1999; 2000). In contrast, phosphorus is the primary
limiting nutrient in most freshwater systems (Hecky and Kilham 1998). Specifically,
blooms of the nitrogen-fixing blue-green alga Anabaena sp., as well as filamentous
green algae, have been above the NCDWQ standard for chlorophyll a concentrations
indicative of algal-impaired water. Such blooms possibly reflect in part the biological impact of animal waste contributed by waterfowl. The purpose of this study was to
determine the spatial and temporal pattern of waterfowl on Greenfield Lake, to
determine if significant correlations exist between waterfowl abundance and
phosphorus, nitrogen, and fecal coliform bacteria from the water column, and to
calculate potential nutrient contribution by bird guano.
Methods
From August 2000 to July 2001, waterfowl inhabiting the lake were counted using
8 X 42 binoculars four to six times each month. Surveys either occurred within two hours
after sunrise or two hours prior to dusk. Seven sites around the perimeter of the lake were chosen for stationary counts (Fig. 1). These stations were selected because they
had high visibility across the lake surface, and/or because waterfowl commonly roosted or
foraged on land at the site. Birds on the water, in trees on the water, or on the shore
were included. In this study, the shore was delimited by the road surrounding the lake.
Water samples were collected monthly approximately 5 cm under the surface of
the water, and they were processed for nutrients and fecal coliform bacteria by a state-
certified contract laboratory using EPA and APHA techniques. At sites 1, 2, 6, and 7 total
bird population was summed by date and averaged monthly to test for significant
correlation with nutrients and fecal coliform bacteria found in monthly water samples at
station GL-P. Likewise, sites 3, 4, and 5 were close in proximity to the Wilmington Watersheds station GL-YD, and counts achieved at these sites were compared to results
from water samples taken monthly at GL-YD. Total bird count was averaged monthly and
tested for significant correlation to the lake monthly mean nutrients and fecal coliform as
well. Nutrient and bacteria means were calculated using three in-lake Wilmington
Watersheds Project stations (GL-P, GL-YD, and GL-2340). Precipitation data for the Wilmington area was compared to water quality parameters as well. Rainfall daily
measurements were retrieved from the National Weather Service web site
(http://nwsilm.wilmington.net/climate/ilm/ilmdata.html ). Average daily precipitation in
inches between water sampling days and the precipitation sum 72 , 48, and 24 hours
prior to sampling were tested for correlation to nitrogen, phosphorus and fecal coliform concentrations found at GL-P, GL-YD, and for the in-lake mean. Pairwise correlations
were completed using JMPIN statistical software (Version 3.2.1, 1996, SAS institute,
Inc.). Correlations with p < 0.05 were considered significant.
To calculate total nitrogen (TN) and total phosphorus (TP) input by birds on the
water and shore surrounding the lake, waterfowl were grouped by size and ecological niche (Table 1). For example, all dabbling ducks were summed for a daily count, and
then each count averaged for every month. Waterfowl use days were estimated monthly
for all bird categories by multiplying the mean count by the number of days in the month.
Methods used by Manny et al.(1994) to estimate total nitrogen (TN) and total phosphorus
(TP) defecated by ducks were incorporated to calculate “equivalent, effective goose-use days” for dabbling ducks, diving ducks, American Coots (Fulica americana), and Muscovy
Ducks (Podilymbus podiceps). It was assumed that because these birds share similar
diets, leafy vegetation, seeds, and invertebrates (Ehrlich et al. 1988) and digestive
processes, they likely excrete equivalent nutrients relative to body weight. Nutrients from
gulls, cormorants, and herons were estimated based on percentages of nutrients found in
their guano (see Marion et al. 1994). For Pied-billed Grebes (Podilymbus podiceps),
nutrients contributed were derived by multiplying each monthly mean number of grebes per day by the ratio of grebe body weight to cormorant body weight and again by the
estimated nutrients excreted daily by a cormorant. Pied-billed Grebes mostly eat aquatic
invertebrates and fish, a carnivorous diet similar to cormorants (Erhlich et al. 1988).
Cormorants were observed mostly on the lake prior to dusk and use the lake as a night
roosting area in the winter. Therefore, to calculate TN and TP excreted into the lake by cormorants, daily estimates were divided by half representing only the evening hours. No
other birds displayed patterned absences from the lake, and were assumed to utilize the
lake habitat all day.
Estimated percent of TN and TP contributed by each bird group was calculated using the weight in mg of TN and TP excreted monthly by birds on the water. This weight
estimate was divided by the volume of the lake, then the resulting number was divided by
the mean nutrient concentration found in the water column (mg/L) for that month; the
dividend was then multiplied by 100. Only waterfowl observed on the water were included
in the calculations of percent. Residence time of lake water was not determined.
Results
In all areas waterfowl counts were highest in winter, particularly November
through February (Tables 2, 3, and 4). Monthly waterfowl population counts on
Greenfield Lake were not spatially correlated with nutrients or fecal coliform bacteria at
GL-P, GL-YD, or for the entire lake (Table 2, 3, and 4). The only water quality
parameter bird abundance was correlated with was dissolved oxygen, indicating that bird abundance was greatest in winter, when dissolved oxygen concentrations are
highest. Average daily rainfall between sampling days was correlated to TN
concentration for the entire lake (r = 0.730, p < 0.007), and at GL-YD it was significantly
correlated both with TN (r = 0.66, p = 0.03) and nitrate (r = 0.617; p = 0.043). At GL-YD
nitrate was also significantly correlated with rain in the prior 72 hours (r = 0.786; p= 0.004) and 48 hours (r = 0.764; p = 0.006). For GL-P, average precipitation was
"borderline" correlated with TN concentration (r = 0.574, p = 0.051). TP was not
correlated to rainfall during the months of sampling. Fecal coliform bacteria
concentration was significantly correlated with the 72 hour sum of rainfall prior to
sampling at GL-YD (r = 0.745, p < 0.009), as well as with the 48 hour rainfall sum (r = 0.789; p = 0.004). However, fecal coliforms were not significantly correlated with birds
or rainfall at GL-P or the entire lake.
Strong positive correlations were found at GL-P between chlorophyll a and
turbidity (r = 0.953; p = 0.001) and BOD5 (r = 0.873; p = 0.002). Likewise, BOD5 was
correlated with turbidity (r = 0.942; p = 0.001) and total suspended solids (r = 0.811; p = 0.008). Chlorophyll a was also correlated with turbidity at GL-YD (r = 0.942; p = 0.003)
and for the entire lake (r = 0.658; p = 0.020). This indicates that the majority of in-lake
turbidity and suspended matter is algal in origin.
Estimated concentrations of TN and TP contributed by waterfowl feces were highest in the winter months, when some monthly input estimates exceeded 100% of
the TP sampled from the water column (Table 5). The estimated dry weight of TP
excreted by waterfowl both on the water and the surrounding shore of the lake indicated
highest weights to be contributed by cormorants (Table 6), with annual TP input
estimated to be about 66,534 g dry weight. Furthermore, of all the bird groups, cormorants were estimated to contribute the highest average percent of TP found in the
water column per month (Table 1; Table 6). Estimates calculated for percent nitrogen
input by birds in relation to TN concentration in water samples (Table 5) indicate that
waterfowl input was the highest during January (21%) when populations of American
Coots, Canada Geese, and Dabbling Ducks increased. However, TN in the water column decreased during January for the in-lake mean to only 0.105 mg/L (Table 4).
Great (Phalacrocorax carbo) and Double-crested Cormorants (P. auritus),
Canada Geese (Branta canadensis), and American Widgeons (Mareca americana) (a
dabbling duck) were most abundant during the winter months, and out of all other birds,
the groups including these species likely excreted the greatest amount of TN into the water at GL-YD. Similarly, the American Coot population peaked during the winter
months with a daily abundance ranging from an average of 169.3 (SE = ± 46.8) in
December to 304.7 (SE = ± 32.0) in February. Calculations of nutrients defecated by
American Coots yielded the greatest amount of TN to the water nearby GL-P, an
annual amount of approximately 9,279 g dry weight. At GL-P, they were frequently observed foraging on submerged macrophytes.
Discussion
Water quality at Greenfield Lake may be affected by waterfowl abundance over several months and years, however this year-long project has shown that nitrogen,
phosphorus and fecal coliform bacteria in the water column were not spatially correlated
to bird abundance during a monthly time period. These results are similar to the
findings of Tobiessen and Wheat (2000) in that no immediate correlation was apparent
between waterfowl abundance to water quality parameters. They suggest that the effect can be witnessed in the long term if waterfowl populations gradually increase.
For example, Anabaena sp. blooms induced by high phosphorus concentrations may
be intensified in the future if the lake’s large wintering cormorant population continues
to rise.
Our data clearly demonstrate that by far the major waterfowl use of Greenfield Lake occurs November through February (Tables 2, 3, and 4). Thus, the major avian
contribution of nutrients also enters the lake during that period. While algal blooms do
occur in winter, they are far more likely to occur in spring and summer when
temperatures and solar irradiance are most favorable. Guanotrophy, especially by
cormorants, likely contributes to a reservoir of phosphorus during the winter months that is then available for uptake by phytoplankton and free-floating macrophytes (such as
duckweed) in warmer months. The formation of blooms of nitrogen-fixing Anabaena sp.
suggest that this is the case as well. Whereas guanotrophy can supply large amounts
of phosphorus to Greenfield Lake in winter, avifauna appear to contribute little nitrogen
to this nitrogen-limited system overall.
The residence time of water and of the nutrients and bacteria in Greenfield Lake
has not been studied, and would provide more insight about nutrient and bacteria
sources to the lake system. Once residence time and all other external sources of
nutrients are determined, methods discussed by Manny et al. (1994) describe how to calculate the amount of nutrients contributed by waterfowl as a percent of the annual
nutrient loading from all external sources. However, one condition that may complicate
this calculation is the annual water level drop in Greenfield Lake during February and
March.
The nitrate form of nitrogen is very mobile and can be subject to rainfall-driven
runoff. This was clearly the case at Station GL-YD, where rainfall was strongly
correlated with nitrate. This is an area that is influenced by tributary streams (the
stream at Lakeshore Commons - GL-LC, and possibly Jumping Run Branch - GL-JRB).
Thus, rain events appear to move nitrate from the watershed into the upper lake area, where it gets taken up by algae as the water passes slowly through the lake.
This study suggests that runoff induced by rainfall could be an important pathway
for nutrients entering the water column of Greenfield Lake. Other likely nutrient inputs
to the system related to precipitation are from direct rainfall, and ground water. The direct relationship of average daily precipitation to TN and nitrate indicates that pulses
of nitrogen from the terrestrial environment are being leached from the watershed more readily than phosphorus. Overestimates of percent TP contributed mostly by tree
roosting cormorants may be explained simply by a low ratio of TP rain washed from the
bark of trees compared to the TP defecated onto trees where the cormorants regularly
roosted. Also, phosphorus readily binds to soil particles and is thus less mobile than
nitrogen. In most areas Greenfield Lake has a good vegetated buffer that prevent erosion of soils into the lake.
Greenfield Lake also provides habitat to numerous turtles that are active in the
spring and summer. It is likely that turtle waste recycles phosphorus and nitrogen into
the water column as well. On several occasions while conducting waterfowl surveys at stations 1, 2, 3, and 4, turtles, resident ducks, and geese were fed bread by park
visitors. Eliminating handouts may affect population abundance of some species
inhabiting the lake, which could in turn reduce the concentration of phosphorus,
nitrogen, and fecal coliform bacteria. However, this study indicates that cormorants add
considerably more TP compared to other bird groups, and cormorants do not feed on handouts from park visitors. Cormorants were observed flying early in the morning west
from the lake towards the direction of the Cape Fear River, then in the evening they
congregated in several cypress trees located in the lake’s center. Cormorants feed
mostly on small fish during the day, therefore, they likely added “new” nutrients into the
lake system whereas other bird species were essentially recycling nutrients from the water and surrounding shoreline. The long-term impact of cormorants utilizing
Greenfield Lake as a roosting habitat could be enriching the sediments with
phosphorus, stimulating the later productivity of algae and free-floating macrophytes
(such as duckweed), and ultimately contributing toward the eutrophication of this urban
lake.
The data indicate that the vast majority of turbidity and suspended solids in
Greenfield Lake are associated with phytoplankton. Also, the well-vegetated shoreline
prevents lakeside sedimentation from occurring. The algal blooms, particularly in the
park area, are strongly correlated with BOD. This indicates that the blooms also have the potential to contribute to periods of hypoxia, especially at night.
Fecal coliform bacteria counts were not spatially correlated with waterfowl
abundance. Bird use was highest at GL-P, followed by GL-YD, but fecal coliform
counts were highest in the tributary streams GL-LB, GL-JRB and GL-LC (see Chapter 6.0A), indicating a watershed-wide input problem that cannot be explained by waterfowl
deposits. Fecal coliform bacteria counts were correlated to the 72 and 48 hour
precipitation sum prior to sampling at GL-YD which is a station that is near residential
lots with large dogs. Additionally, many dog owners walk their dogs around Greenfield
Lake, and many individuals do not clean up their pet’s waste. Thus, it is likely that dog waste enters into the lake nearby this station during rain events, and is carried into the
tributaries from neighborhoods in the upper watershed as well. Local concerned
citizens have reported that stray cats are abundant near residential areas around the
lake, and these animals may be a significant source of fecal coliform bacteria to the
lake tributaries as well. Bacteria contributed by the waterfowl population were not calculated in this study because for some of the most numerous bird groups observed
on Greenfield Lake there is no determined value for bacteria excreted. The variability
of fecal coliform bacteria concentration from one month to the next was high. If fecal coliform bacteria does not remain in the water column for long, waterfowl surveys may
need to be conducted synchronously with water sampling in order to decipher the
degree that birds increase fecal coliform bacteria loading to the lake.
Literature Cited
Benton, C., F. Khan, P. Monoghan, W.N. Richards and C.B. Shedden. 1983. The
contamination of a major water supply by gulls (Larus sp.). Wateresources 17:789-
798.
Ehrlich, P.R., D.S. Dobkin, and D. Wheye. 1988. The Birder’s Handbook: A Field Guide
to the Natural History of North American Birds. Simon & Schuster Inc. New York, New
York.
Gere, G. and S. Andrikovics. 1992. Effects of waterfowl on water quality. Hydrobiologia
243/244:445-448.
Harris, H.J. Jr., J.A. Ladowski and D.J. Worden. 1981. Water-quality problems and
management of an urban waterfowl sanctuary. Journal of Wildlife Management 45:501-507.
Hecky, R.E. and P. Kilham. 1988. Nutrient limitation of phytoplankton in freshwater and
marine environments: A review of recent evidence on the effects of enrichment.
Limnology and Oceanography 33:796-822.
Hussong, D., J. M. Damare, R.J. Limpert, W.J. L. Sladen, R.M. Weiner and R.R. Colwell.
1979. Microbial impact of Canada Geese (Branta Canadensis) and Whistling Swans
(Cygnus columbianus columbianus) on aquatic ecosystems. Applied and
Environmental Microbiology 37:14-20.
Kear, J., 1963. The agricultural importance of wild goose droppings. The 14th Annual
Report of the Wildfowl Trust. P. 72-77.
Mallin, M.A., S.H. Ensign, D.C. Parsons and J.F. Merritt. 1999. Environmental quality of
Wilmington and New Hanover County watersheds 1998-1999. CMSR Report 99-02. Center for Marine Science Research, University of North Carolina at Wilmington,
Wilmington, N.C.
Mallin, M.A., L.B. Cahoon, S.H. Ensign, D.C. Parsons, V.L. Johnson and J.F. Merritt.
2000. Environmental quality of Wilmington and New Hanover County watersheds, 1999-2000. CMS Report No. 00-02. Center for Marine Science, University of North
Carolina at Wilmington, Wilmington, N.C.
Manny, B.A, W.C. Johnson and R.G. Wetzel. 1994. Nutrient additions by waterfowl to lakes and reservoirs: predicting their effects on productivity and water quality.
Hydrobiologia 279/280:121-132.
Marion, L., P. Clergeau, L. Brient and G. Bertru. 1994. The importance of avian
contributed nitrogen (N) and phosphorus (P) to Lake Grand-Lieu, France. Hydrobiologia 279/280:133-147.
Moore, M.V., P. Zakova, K.A. Shaeffer and R.P. Burton. 1998. Potential effects of
Canada Geese and climate change on phosphorus inputs to suburban lakes of the
northeastern U.S.A. Lake and Reservoir Management 14:52-59.
Portnoy, J.W. 1990. Gull contributions of phosphorus and nitrogen to a Cape Cod
kettle pond. Hydrobiologia 202:61-69.
Scherer, N.M., H.L. Gibbons, K.B. Stoops and M. Muller. 1995. Phosphorus loading of an urban lake by bird droppings. Lake and Reservoir Management 11:317-327.
Tobiessen, P. and E. Wheat. 2000. Long and short term effects of waterfowl on Collins
Lake, an urban lake in upstate New York. Lake and Reservoir Management 16:340-
344.
Weiskel, P.K., B.L. Howes and G.R. Heufelder. 1996. Coliform contamination of a
coastal embayment: sources and transport pathways. Environmental Science and
Technology 30:1872-1881.
Table 1. Nutrient input for various bird groups. Formula used to calculate TN and TP from waterfowl count: Average # birds * X * # days in month, where X = grams per day
of nutrient in feces.
Total Nitrogen Total Phosphorus
(g dry weight) (g dry weight)
Geese1 1.57 0.49 Dabbling Ducks2 0.72 0.22
Diving Ducks2 0.61 0.19
Cormorants3 0.89 3.87
Gulls3 0.44 0.24
Egrets & Herons2 0.97 2.64 Coots2 0.28 0.09
Muscovy Ducks2 0.97 0.30
Grebes4 0.20 0.89
1 (Manny et al. 1994) 2 (derived from goose calculation)
3 (Marion et al. 1994)
4 (derived from cormorant calculation)
Table 2. GL-P monthly mean bird counts, nutrient concentrations, fecal coliform bacteria counts (CFU’s), and precipitation data.
________________________________________________________________
Month/yr Bird Count TP TN CFU's Mean precip. 72 hr sum
per day (mg/L) (mg/L) (inches) (inches)
Aug 2000 40.3 0.03 0.98 330 0.28 1.45 Sep 2000 46.2 0.06 0.84 180 0.22 0
Oct 2000 111.8 0.05 0.48 230 0.33 0.24
Nov 2000 235.0 0.01 0.71 420 0 0
Dec 2000 469.7 0.03 0.74 230 0.14 0.13
Jan 2001 413.7 0.23 0.07 100 0.03 0 Feb 2001 429.8 0.08 0.6 400 0.06 0
Mar 2001 478.2 0.25 0.17 590 0.28 4.05
Apr 2001 134.3 0.25 0.22 6,000 0.03 0.11
May 2001 35.6 0.17 0.22 14 0.03 0.13
Jun 2001 31.5 0.21 0.22 2,200 0.15 0.35 Jul 2001 40.7 0.07 2.1 120 0.38 0.57
Table 3. GL-YD monthly mean bird counts, nutrient concentrations, fecal coliform bacteria counts (CFU’s), and precipitation data.
Month/yr Bird Count TP TN CFU's Mean precip. 72 hr sum per day (mg/L) (mg/L) (inches) (inches)
Aug 2000 44.8 1.10 1.34 19 0.28 1.45
Sep 2000 49.4 0.09 0.90 32 0.22 0
Oct 2000 47.0 0.09 2.01 130 0.33 0.24
Nov 2000 114.8 0.07 0.14 13 0 0
Dec 2000 323.3 0.03 0.34 120 0.14 0.13
Jan 2001 274.7 N/A N/A N/A 0.03 0
Feb 2001 152.2 0.07 0.76 909 0.06 0
Mar 2001 85.0 0.22 0.30 2,900 0.28 4.05
Apr 2001 52.3 0.23 0.36 2 0.03 0.11
May 2001 56.6 0.06 0.29 4 0.03 0.13
Jun 2001 53.5 0.12 0.25 1,800 0.15 0.35
Jul 2001 61.8 0.09 0.93 40 0.38 0.57
Table 4. Entire lake monthly mean bird counts, nutrient concentrations, fecal coliform bacteria counts (CFU’s), and precipitation data.
Month/yr Bird Count TP TN CFU's Mean precip. 72 hr sum per day (mg/L) (mg/L) (inches) (inches)
Aug 2000 85.0 0.39 0.91 260 0.28 1.45
Sep 2000 95.6 0.10 0.98 20,071 0.22 0
Oct 2000 158.8 0.08 1.12 320 0.33 0.24
Nov 2000 349.8 0.13 0.46 228 0 0
Dec 2000 793.0 0.03 0.43 317 0.14 0.13
Jan 2001 688.3 0.17 0.11 64 0.03 0
Feb 2001 582.0 0.06 0.85 502 0.06 0
Mar 2001 563.2 0.18 0.31 1,312 0.28 4.05
Apr 2001 186.7 0.18 0.27 2,164 0.03 0.11
May 2001 92.2 0.08 0.36 49 0.03 0.13
Jun 2001 85.0 0.14 0.36 1,733 0.15 0.35
Jul 2001 102.5 0.08 1.91 73 0.38 0.57
Table 5. Estimated percent of total Greenfield Lake nitrogen and phosphorus load contributed monthly by waterfowl observed on the surface.
% TN % TP
Aug 2000 0 0
Sep 2000 0 1
Oct 2000 0 4
Nov 2000 2 5
Dec 2000 5 209
Jan 2001 21 24
Feb 2001 2 36
Mar 2001 4 13
Apr 2001 2 5
May 2001 1 6
Jun 2001 1 1
Jul 2001 0 2
Table 6. Average estimated percent of total Greenfield Lake nitrogen and phosphorus load excreted by individual bird groups into the lake.
% TN % TP
Diving Ducks 0 0
Dabbling Ducks 1 1
Geese 1 1
Muscovy Ducks 0 0
Coots 1 1
Cormorants 1 21
Gulls 0 0
Herons 0 2
Grebes 0 1
Total 4% 27%
7.0 Hewletts Creek
Hewletts Creek was sampled at seven tidally-influenced areas (HC-M, HC-2, HC-
3, HC-NWB, NB-GLR, MB-PGR and SB-PGR) and one freshwater runoff collection
area draining Pine Valley Country Club (PVGC-9 - Fig. 7.1). Physical data indicated
that turbidity was well within State standards on almost all occasions (Tables 7.1 and 7.2). There were several incidents of hypoxia in the spring and summer months at NB-
GLR and SB-PGR. Nitrate concentrations were high in the middle branch (MB-PGR),
which drains both Pine Valley and the Wilmington Municipal Golf Courses (Fig. 7.1;
Mallin and Wheeler 2000). Both NB-GLR and SB-PGR also periodically receive
elevated nutrient loading as well. Median N/P molar ratios demonstrated that both HC-2 and HC-3 should be primarily nitrogen limited, while NB-GLR tends toward potential
phosphorus limitation and SB-PGR could be either. The chlorophyll a data (Table 7.1)
showed that Hewletts Creek continues to host periodic algal blooms at SB-PGR, as it
has in the past (Mallin et al. 1998a; 1999).
Fecal coliform bacterial counts showed that the only stations fit for shellfishing were HW-M (at the mouth) and HW-2 (Fig. 7.1). Both had less than 10% of the
samples exceeding 43 CFU/100 mL, and low geometric means (Table 7.1). All five
stations upstream of HC-3 were generally unfit for human contact. The percent of
counts exceeding 200 CFU/100 mL were 40% at HC-NWB, 50% at NB-GLR, 75% at
MB-PGR, 33% at SB-PGR, and 75% at PVGC-9.
Phosphate and nitrate were elevated leaving the course, but nitrate increased
even more downstream at MB-PGR (Tables 7.1 and 7.2). Inputs from Municipal Golf
Course or suburban sources may have accounted for the increase. Fecal coliform
bacteria counts exceeded state standards 75% of the time in 2000-2001 at PVGC-9. An earlier assessment (Mallin and Wheeler 2000) noted higher fecal coliform counts
entering the course from suburban neighborhoods upstream than counts at PVGC-9
leaving the course. The highest monthly count (2,000 CFU/100 mL) occurred in March
2001. A collaborative effort among Pine Valley Country Club, New Hanover County,
Cape Fear Resource Conservation and Development, the Clean Water Management Trust Fund, the New Hanover County Tidal Creeks Program, the N.C. State
Cooperative Extension Service at North Carolina State University, the City of
Wilmington and UNCW is effecting continuing restoration work on the course that is
expected to improve downstream water quality in upcoming years.
Table 7.1. Selected water quality parameters at lower creek stations in Hewletts Creek watershed as mean (standard deviation) / range, August 2000-July 2001.
_____________________________________________________________________
Parameter HC-M HC-2 HC-3 HC-NWB
_____________________________________________________________________
Salinity 34.6 (1.0) 34.3 (1.2) 31.2 (4.1) 22.2 (12.4)
(ppt) 31.1-36.0 34.3 (1.2) 31.2 (4.1) 22.2 (12.4)
Turbidity 4 (3) 4 (2) 5 (4) 8 (6)
(NTU) 1-11 1-8 2-12 2-18
DO 7.8 (1.4) 7.6 (1.4) 7.2 (1.5) 6.9 (2.0)
(mg/L) 5.2-9.8 5.6-9.8 4.7-9.5 3.9-10.3
Nitrate 0.005 (0.005) 0.005 (0.004) 0.011 (0.010) 0.043 (0.064) (mg/L) 0.001-0.017 0.001-0.017 0.001-0.031 0.001-0.208
Ammonium 0.016 (0.011) 0.019 (0.012) 0.023 (0.010) NA
(mg/L) 0.001-0.028 0.003-0.042 0.007-0.038
Phosphate 0.004 (0.002) 0.005 (0.003) 0.006 (0.003) 0.009 (0.007)
(mg/L) 0.001-0.007 0.001-0.009 0.001-0.012 0.002-0.022
Mean N/P 14.5 14.4 16.2 NA
Median 11.9 12.0 11.8
Chlor a 1.4 (1.3) 1.6 (1.1) 2.1 (1.9) 3.6 (3.3)
(ug/L) 0.2-5.1 0.4-3.5 0.3-6.4 0.2-8.6
Fecal coliforms 2 2 11 68
CFU/100 mL 0-200 0-129 0-200 3-740 _____________________________________________________________________
Table 7.2. Selected water quality parameters at upstream stations in Hewletts Creek watershed, as mean (standard deviation) / range, fecal coliforms as geometric mean /
range, August 2000-July 2001.
_____________________________________________________________________
Parameter NB-GLR SB-PGR MB-PGR PVGC-9
_____________________________________________________________________
Salinity 15.4 (11.1) 16.6 (10.8) 0.2 (0.3) 0.1 (0.0)
(ppt) 1.1-32.3 2.0-33.4 0.1-1.1 0.1-0.1
Turbidity 10 (6) 14 (9) 6 (5) 11 (16) (NTU) 2-18 4-30 1-20 1-53
DO 6.5 (2.0) 6.9 (2.0) 7.0 (1.2) 6.7 (1.8)
(mg/L) 3.5-9.5 4.8-10.6 5.5-9.0 3.9-9.7
Nitrate 0.079 (0.060) 0.062 (0.076) 0.235 (0.057) 0.326 (0.222)
(mg/L) 0.008-0.221 0.001-0.270 0.160-0.334 0.040-0.780
Ammonium 0.042 (0.029) 0.034 (0.025) 0.032 (0.013) 0.043 (0.023)
(mg/L) 0.010-0.108 0.012-0.081 0.014-0.053 0.005-0.080
Phosphate 0.013 (0.007) 0.012 (0.009) 0.016 (0.007) 0.043 (0.030)
(mg/L) 0.006-0.027 0.003-0.038 0.006-0.034 0.005-0.090
Mean N/P ratio 22.6 24.7 51.6 42.7 Median 24.9 22.6 36.9 17.7
Chlor a 6.3 (6.4) 13.9 (13.7) 1.3 (1.4) 2.8 (2.3)
(ug/L) 0.8-18.3 0.8-38.2 0.3-5.5 0.5-7.1
Fecal coliforms 68 118 266 362 CFU/100 mL 3-740 9-2000 79-2000 132-2000
_____________________________________________________________________
8.0 Howe Creek Water Quality
Howe Creek was sampled for physical parameters, nutrients, and chlorophyll a
at three locations during 2000-2001 (HW-FP, HW-GC, and HW-GP, Fig. 8.1). Howe
Creek did not show any unusual water quality problems in 2000-2001 at the three
stations sampled. Turbidity was low near the ICW and exceeded North Carolina water
quality standards on only one occasion at HW-GC (Table 8.1; Appendix B). Dissolved oxygen concentrations were generally good in Howe Creek. Fecal coliform bacteria
were not sampled in Howe Creek during 2000-2001. Nutrient levels are low near the
ICW but can be elevated in the creek near Graham Pond (Table 8.2). Median inorganic
molar N/P ratios were low to medium, indicating that nitrogen is probably the principal
limiting nutrient at stations downstream of HW-GP.
Table 8.1. Water quality summary statistics for Howe Creek, August 2000-July 2001,
as mean (st. dev.) / range.
Salinity Diss. oxygen Turbidity Chlor a
(ppt) (mg/L) (NTU) (µg/L) _____________________________________________________________________
HW-FP 34.6 (1.0) 7.4 (1.5) 4 (3) 2.0 (2.1)
32.4-35.8 5.2-9.5 0-9 0.2-7.0
HW-GC 30.2 (5.5) 7.4 (1.7) 8 (7) 2.3 (2.4) 20.0-35.1 4.9-10.0 3-26 0.5-7.4
HW-GP 18.7 (12.4) 6.8 (1.6) 9 (5) 8.0 (9.1)
0.9-33.7 4.0-9.7 3-20 0.7-22.7
Table 8.2. Nutrient concentration summary statistics for Howe Creek, August 2000-July 2001, as mean (st. dev.) / range, N/P ratio as mean / median.
_____________________________________________________________________
Nitrate Ammonium Phosphate Molar N/P ratio
(mg/L) (mg/L) (mg/L) _____________________________________________________________________
HW-FP 0.004 (0.002) 0.022 (0.009) 0.005 (0.003) 15.8
0.001-0.008 0.009-0.040 0.001-0.010 11.6
HW-GC 0.005 (0.004) NA 0.006 (0.003) NA 0.001-0.012 0.002-0.010
HW-GP 0.023 (0.026) 0.041 (0.034) 0.007 (0.004) 22.2
0.001-0.066 0.007-0.135 0.001-0.010 17.4 ____________________________________________________________________
9.0 Motts Creek
Mott’s Creek near River Road has been classified by the State of North Carolina
as a Natural Heritage Site because of the area’s biological attributes. These include
the pure stand wetland communities, including a well-developed sawgrass community
and unusually large flats dominated by Lilaeopsis chinensis and spider lily, with large
cypress in the swamp forest. Thus, it is important that these attributes should be protected from land and water-disturbing activities. UNCW scientists sampled Mott’s
Creek at the River Road bridge (Fig. 9.1). A large development is under construction
upstream of the sampling site and between Mott’s and Barnard’s Creeks.
Dissolved oxygen concentrations were below 5.0 mg/L on 25% of the occasions
sampled in 2000-2001, and there was one major algal bloom of 49 µg/L in May 2001
(Table 9.1). As part of a new UNCW effort BOD5 was sampled on six occasions in
2001, yielding a mean value of 0.9 mg/L and a median value of 0.8 mg/L. Turbidity was
periodically a problem, exceeding the state standard of 25 NTU on two of twelve occasions. This station also maintained some of the higher suspended solids levels in
the system. Fecal coliform contamination was a problem in Mott’s Creek, with the
geometric mean of 269 CFU/100 mL well exceeding the state standard of 200 CFU/100
mL, and monthly samples exceeding this standard on eight of twelve occasions
(Appendix B). Thus, this creek already has some water quality problems. Development activities upstream, if not done in an environmentally-sound manner, will only lead to
further degradation of both Mott’s and Barnard’s Creeks.
Table 9.1. Selected water quality parameters at a station (MOT-RR) draining Motts Creek watershed before entering the Cape Fear Estuary, as mean (standard deviation)
/ range, August 2000-July 2001. Fecal coliforms as geometric mean / range.
_____________________________________________________________________
Parameter MOT-RR
_____________________________________________________________________
Salinity (ppt) 2.6 (3.8)
0.1-13.3
TSS (mg/L) 14.6 (8.7) 4.0-37.0
Turbidity (NTU) 16 (9)
7-36
DO (mg/L) 6.2 (1.5)
3.3-8.4
Nitrate (mg/L) 0.142 (0.137)
0.005-0.400
Ammonium (mg/L) 0.026 (0.023)
0.005-0.080
Total nitrogen (mg/L) 0.685 (0.514) 0.080-2.100
Phosphate (mg/L) 0.055 (0.033)
0.010-0.130
Total phosphorus (mg/L) 0.095 (0.054)
0.020-0.200
Mean N/P ratio 9.1
Median 8.0
Chlor a (µg/L) 9.2 (14.0)
1.3-48.9
Fecal coliforms (CFU/100 mL) 269 90-540
_____________________________________________________________________
10.0 Pages Creek
Pages Creek was sampled at nine stations, two of which receive drainage from
developed areas (PC-BDUS and PC-BDDS - Fig. 10.1). There has been recent
drainage system modification in the vicinity of PC-BDUS. During the past sample year
turbidity was low with only two incidents of turbidity exceeding the state standard of 25 NTU, both at BC-BDUS (Table 10.1). However, there were several incidents of hypoxia
during summers of 2000 and 2001, including three each at stations draining Bayshore
Drive (Appendix B). Nutrient concentrations were normally low, and phytoplankton
biomass was low with no algal blooms noted (Tables 10.1 and 10.2). Inorganic
nitrogen-to-phosphorus molar ratios were below 16, indicating that phytoplankton growth in this creek is probably nitrogen limited.
Table 10.1. Selected water quality parameters in lower Pages Creek as mean
(standard deviation) / range, August 2000-July 2001.
_____________________________________________________________________ Parameter PC-M PC-OL PC-CON PC-OP PC-LD
_____________________________________________________________________
Salinity 34.1 (1.2) 33.9 (1.3) 34.1 (1.2) 33.3 (2.3) 34.2 (1.3)
30.8-35.4 30.3-35.2 31.2-35.6 26.7-35.4 30.5-35.6
Turbidity (NTU) 7 (5) 6 (5) 7 (6) 6 (5) 7 (6)
1-16 1-16 1-19 0-17 1-21
DO (mg/L) 7.3 (1.5) 7.3 (1.5) 7.2 (1.6) 6.5 (1.9) 7.0 (1.6) 4.7-9.9 4.5-9.8 4.4-10.0 3.9-9.9 4.2-9.7
Nitrate (mg/L) 0.004(0.004) 0.004(0.004) 0.006(0.004) 0.007(0.006) 0.005(0.003)
0.001-0.012 0.001-0.013 0.002-0.014 0.001-0.020 0.001-0.012
Ammonium (mg/L) 0.027(0.012) NA NA NA NA
0.012-0.041
Phosphate (mg/L) 0.006(0.003) 0.007(0.003) 0.007(0.003) 0.008(0.004) 0.007(0.003)
0.002-0.012 0.002-0.013 0.001-0.013 0.002-0.014 0.001-0.015
Mean N/P Ratio 12.7
median 12.8 NA NA NA NA
Chlor a (µg/L) 2.4 (2.2) 2.4 (2.3) 2.3 (2.3) 2.2 (2.2) 1.9 (1.8)
0.2-6.4 0.2-7.1 0.2-7.1 0.1-6.2 0.2-6.2
Fecal coliforms 1 2 2 5 2
CFU/100 mL 0-14 0-20 0-21 0-25 1-22
_____________________________________________________________________
Fecal coliform sampling showed that the lower creek continues to present good conditions for shellfishing, and the upper creek was well within standards for human
contact as well. Because of the relatively low watershed development and low amount
of impervious surface coverage in the watershed (Mallin et al. 1998a; 2000b), this is
one of the least-polluted tidal creeks in New Hanover County.
Table 10.2. Selected water quality parameters in upper Pages Creek as mean
(standard deviation) / range, August 2000-July 2001.
_____________________________________________________________________
Parameter PC-BDDS PC-WB PC-BDUS PC-H
_____________________________________________________________________
Salinity 31.6 (2.8) 30.8 (2.9) 25.6 (4.9) 30.1 (3.0)
25.8-35.1 25.3-34.8 13.8-31.0 25.5-33.6
Turbidity (NTU) 7 (3) 8 (6) 13 (12) 7 (3) 2-14 1-23 2-36 2-13
DO (mg/L) 6.2 (1.9) 6.4 (1.8) 5.9 (1.7) 6.4 (2.3)
3.0-9.6 3.5-9.3 2.9-9.1 3.3-10.1
Nitrate (mg/L) 0.020(0.018) 0.010(0.009) 0.015(0.011) 0.010(0.009)
0.003-0.062 0.001-0.031 0.002-0.037 0.002-0.026
Ammonium (mg/L) 0.031(0.013) NA 0.059(0.034) 0.033(0.025)
0.014-0.049 0.021-0.132 0.009-0.060
Phosphate (mg/L) 0.009(0.003) 0.010(0.003) 0.014 (0.005) 0.010(0.004)
0.003-0.013 0.004-0.015 0.007-0.021 0.003-0.017
Mean N/P Ratio 9.7 NA 12.0 9.8 median 10.1 11.3 9.0
Chlor a (µg/L) 3.5 (3.8) 3.5 (3.9) 4.7 (5.8) 2.9 (2.8)
0.4-12.7 0.2-11.3 0.5-21.4 0.4-7.6
Fecal coliforms 30 12 37 28
CFU/100 mL 7-126 1-124 10-140 5-200
_____________________________________________________________________
11.0 Smith Creek
Two estuarine sites on Smith Creek proper, SC-23 and SC-CH (Fig. 11.1) were
sampled. Dissolved oxygen concentrations were below 5.0 mg/L on three of 12
occasions at both SC-CH and SC-23. Thus, low dissolved oxygen continued to be a
water quality problem in Smith Creek. The North Carolina turbidity standard for estuarine waters (25 NTU) was exceeded on four of 12 occasions at SC-CH and two of
12 occasions at SC-23, an increase over last year. These two stations also maintained
some of the higher suspended solids concentrations in the Wilmington watersheds
system.
On average, most nutrient concentrations were unremarkable, with no defined
spatial pattern (Table 11.1). Algal blooms of 34.5 µg/L and 41.7 µg/L of chlorophyll a
occurred at SC-23 in May and June 2001, respectively. Fecal coliform bacteria levels
exceeded the North Carolina standard for human contact waters (200 CFU/100 mL)
four times at SC-23 and three times at SC-CH during the twelve sample trips; thus, fecal coliform pollution continues to be a problem in Smith Creek (Appendix B). The
geometric mean fecal coliform concentration was below the human contact standard at
both stations but well above the shellfishing standard (14 CFU/100 mL) in the estuarine
portion of the creek (Table 11.1). The highest monthly counts occurred in March 2001,
when Station SC-23 yielded 2,300 CFU/100 mL and SC-CH 1000 CFU/100 mL. As part of a new UNCW effort, BOD5 was sampled on six occasions in 2001 at SC-CH,
with a mean value of 1.3 mg/L and a median value of 0.9 mg/L. Smith Creek has been
targeted for restoration by the North Carolina Wetlands Restoration Program, and an
additional UNCW sampling effort funded by the WRP was initiated in summer 2001.
Table 11.1. Selected water quality parameters in Smith Creek watershed as mean (standard deviation) / range. August 2000-July 2001.
_____________________________________________________________________
Parameter SC-23 SC-CH
_____________________________________________________________________
Salinity (ppt) 0.5 (0.6) 1.8 (2.7)
0.1-1.9 0.1-7.4
Dissolved oxygen (mg/L) 6.5 (1.9) 6.7 (1.9)
3.9-9.6 3.9-10.2
Turbidity (NTU) 16 (12) 18 (13)
5-46 8-42
TSS (mg/L) 13.2 (9.6) 16.0 (14.5) 1.0-39.0 3.0-50.0
Nitrate (mg/L) 0.095 (0.067) 0.149 (0.116)
0.005-0.210 0.005-0.290
Ammonium (mg/L) 0.033 (0.026) 0.029 (0.023)
0.005-0.090 0.005-0.080
Total nitrogen (mg/L) 0.675 (0.550) 0.697 (0.580)
0.190-2.100 0.100-2.200
Phosphate (mg/L) 0.053 (0.023) 0.063 (0.026)
0.010-0.100 0.030-0.110
Total phosphorus (mg/L) 0.119 (0.101) 0.142 (0.072) 0.040-0.380 0.050-0.290
Chlor. a (µg/L) 10.7 (13.8) 5.6 (7.6)
0.4-41.7 0.3-21.9
Fecal col. /100 mL 122 104
(geomean / range) 13-2300 21-1000
_____________________________________________________________________
12.0 Upper and Lower Cape Fear
Within the Wilmington City limits drainage directly to the Cape Fear River (CFR)
was sampled at one location each in the Upper and Lower Cape Fear Watersheds.
The stream draining the Upper CFR was sampled behind the Wilmington Police Station
between 2nd and 3rd Streets (Fig. 12.1). Concentrations of most physical, chemical and biological constituents were low to moderate except for nitrate (Table 12.1), which was
elevated at times. We note that overall nitrate has continued to decrease from earlier
study years. The geometric mean fecal coliform count for UCF was 484 CFU/100 mL
for the past year, similar to last year's 486 CFU/ 100 mL and well in excess of the state
standard of 200 CFU/100 mL.
Drainage from the Lower CFR was sampled from the stream draining Greenfield
Lake (Fig. 12.1). Processing within the lake served to keep concentrations of most
constituents relatively low (Table 12.1). Most parameters were below state water
quality standards during the sampling period. However, algal blooms within the lake are occasionally transported over the dam to the river through this station. This is also
reflected in periodic high turbidities (Appendix B). Fecal coliform counts exceeded the
state standard 17% of the time sampled, an improvement over last year's 58%
(Appendix B).
Table 12.1. Water quality summary statistics (mean (standard deviation) / range) for
Wilmington Upper (UCF) and Lower (LCF) Cape Fear Watersheds, 2000-2001.
_____________________________________________________________________
Station DO (mg/L) Turbidity (NTU) TSS (mg/L) Fecal col (CFU/100 mL) _____________________________________________________________________
UCF 8.2 (0.8) 2.0 (2.0) 3.2 (2.6) 484
7.0-9.7 0.1-4.0 0.5-8.3 81-4200
LCF 8.4 (2.7) 17.0 (27.0) 7.2 (5.9) 65
5.2-14.7 1.0-85.0 2.0-22.0 2-220
_____________________________________________________________________
Nitrate (mg/L) Ammonium (mg/L) Phosphate (mg/L) Chlor a (µg/L)
_____________________________________________________________________
UCF 0.636 (0.770) 0.018 (0.014) 0.045 (0.020) 0.9 (1.0)
0.020-2.300 0.005-0.050 0.010-0.080 0.0-3.0
LCF 0.016 (0.019) 0.160 (0.286) 0.041 (0.037) 21.6 (31.9)
0.005-0.070 0.005-1.000 0.005-0.130 0.2-99.4
_____________________________________________________________________
13.0 Whiskey Creek
Sampling of Whiskey Creek began in August 1999. Five stations were chosen;
WC-M (at the marina near the creek mouth), WC-AB (off a private dock upstream),
WC-MLR (from the bridge at Masonboro Loop Road), WC-SB (in fresh to oligohaline
water along the south branch at Hedgerow Lane), and WC-NB (in fresh to oligohaline water along the north branch at Navajo Trail – Fig. 13.1). Dissolved oxygen
concentrations were below the State standard 17% of the time at four out of five
stations in 2000-2001 (Table 13.1). Turbidity was normally within state standards for
tidal waters except for three occasions at Station WC-MLR (Appendix B). There were
no excessive algal blooms during this period; chlorophyll a concentrations were usually
low (Table 13.1). Nitrate concentrations were highest upstream at WC-NB, followed by WC-SB (Table 13.2). However, phosphate concentrations were similar among all
stations. Phosphate, ammonium and nitrate at WC-MB were highest among all creek
mouth stations in the tidal creek system. Fecal coliform bacteria were not sampled in
Whiskey Creek during this period.
Table 13.1. Water quality summary statistics for Whiskey Creek, August 2000-July
2001, as mean (st. dev.) / range.
Salinity Dissolved oxygen Turbidity Chlor a
(ppt) (mg/L) (NTU) (µg/L)
_____________________________________________________________________ WC-MB 31.2 (3.56) 6.8 (1.6) 6 (4) 2.7 (2.3)
24.1-35.0 3.8-9.2 2-11 0.3-6.6
WC-AB 27.7 (4.8) 6.8 (1.7) 11 (7) 4.2 (4.5) 19.7-34.1 3.6-9.1 2-27 0.3-14.7
WC-MLR 19.9 (9.0) 7.0 (1.7) 13 (12) 5.6 (6.1)
5.5-33.2 4.0-9.1 3-40 0.6-18.8
WC-SB 0.1 (0.0) 7.1 (1.5) 5 (7) 1.4 (1.4) 0.0-0.2 3.0-8.6 3-27 0.2-4.7
WC-NB 0.2 (0.0) 6.2 (1.7) 6 (6) 1.0 (1.1)
0.1-0.2 3.0-8.5 1-23 0.1-2.9
Table 13.2. Nutrient concentration summary statistics for Whiskey Creek, August 2000-July 2001, as mean (st. dev.) / range, N/P ratio as mean / median.
_____________________________________________________________________
Nitrate Ammonium Phosphate Molar N/P ratio
(mg/L) (mg/L) (mg/L)
_____________________________________________________________________
WC-MB 0.015 (0.013) 0.034 (0.019) 0.010 (0.004) 11.2
0.003-0.043 0.015-0.070 0.004-0.016 10.8
WC-AB 0.019 (0.013) NA 0.012 (0.005) NA 0.004-0.047 0.004-0.021
WC-MLR 0.018 (0.015) 0.045 (0.034) 0.012 (0.008) 13.8
0.004-0.047 0.007-0115 0.003-0.031 15.1
WC-SB 0.050 (0.014) 0.098 (0.036) 0.003 (0.004) 327.6
0.021-0.074 0.029-0.151 0.001-0.016 298.6
WC-NB 0.170 (0.079) 0.099 (0.032) 0.011 (0.023) 260.2
0.029-0.302 0.041-0.155 0.001-0.082 87.9 _____________________________________________________________________
14.0 Little Creek
The Aquatic Ecology Laboratory was asked to conduct a special survey of Little
Creek, located between Pages and Futch Creeks on the Atlantic Intracoastal
Waterway. As such, in 2001 we collected data on four occasions, April through July.
Nearby residents had voiced concerns about potential water quality impacts from nearby construction activities. We therefore sampled the creek at three locations. LC-
M is near the creek mouth, LC-C is located about halfway up the creek, and LC-LO is
located upstream near Live Oak Dr.
Table 10.1. Selected water quality parameters in Little Creek as mean (standard deviation) / range, April 2001-July 2001. Fecal coliforms are geometric mean / range.
_____________________________________________________________________
Parameter LC-M LC-C LC-LO
_____________________________________________________________________
Salinity 36.3 (0.5) 36.1 (0.3) 36.2 (0.5)
ppt 35.4-36.5 35.8-36.4 35.3-36.4
Dissolved Oxygen 5.5 (0.8) 4.9 (0.9) 5.3 (0.6)
mg/L 5.1-6.8 4.0-5.7 4.7-6.0
Turbidity 7 (3) 12 (5) 8 (1)
NTU 5-11 6-16 7-9
Nitrate 0.005 (0.001) 0.004 (0.001) 0.006 (0.001) mg/L 0.004-0.006 0.004-0.005 0.005-0.007
Phosphate 0.007 (0.001) 0.009 (0.001) 0.011 (0.003)
mg/L 0.006-0.008 0.008-0.010 0.010-0.016
Chlorophyll a 1.7 (0.3) 2.2 (0.9) 2.8 (1.2)
ug/L 1.3-2.0 1.2-2.9 1.2-3.6
Fecal coliforms 13 4 19
CFU/100 mL 4-200 3-9 8-42
_____________________________________________________________________
Based on four sampling occasions, Little Creek is a high salinity system with few
water quality problems. Sampling was conducted during late spring and summer, the
period of lowest dissolved oxygen in the tidal creek system. Thus, dissolved oxygen
was between 4.0 and 5.0 mg/L on three occasions. Turbidity was well below the State standard on all occasions at all sites. Nitrate and orthophosphate concentrations were
low as well. Even though samples were collected in spring and summer, when
phytoplankton biomass is usually highest, chlorophyll a samples were low on all
occasions at all sites. This was no doubt a reflection of the very low nutrient
concentrations present. Fecal coliform samples were below the shellfishing standard of 14 CFU/100 mL at the creek mouth and mid-creek sites except for one incident of 200
CFU/100 mL at the mouth station LC-M in July. Since this incident occurred at the station farthest from land, this contamination may have resulted from a nearby marina
rather than runoff. The uppermost station yielded fecal coliform levels in excess of the
shellfishing standard, but well below the human contact standard. Thus, based on
limited data, Little Creek was in generally good condition, although there is potential for
occasional fecal bacterial contamination.
15.0 Soil Phosphorus, Land Use, and Phosphorus Loading to New Hanover County Tidal
Creeks
by
Lawrence B. Cahoon
Department of Biological Sciences
University of North Carolina at Wilmington
Wilmington, NC
Introduction
Nutrient loading is recognized as a significant water quality problem, particularly
for the rapidly developing coastal region of North Carolina, where a combination of point- and non-point nutrient sources contribute to the problem. Point-source
discharges of effluents from sewage systems, industries, and other waste generators
have been regulated by the Clean Water Act through the National Pollutant Discharge
Elimination System (NPDES) since 1972. Non-point discharges, particularly storm water
runoff, have not been regulated until very recently, however, and are now thought to contribute a majority of the total pollutant loads to surface waters.
Non-point sources of nutrients are, almost by definition, much more difficult to
measure and regulate than nutrient loading from point sources. Furthermore,
differences in the biogeochemical cycles of the major nutrient elements, nitrogen and phosphorus, require different methods to evaluate the magnitude of loading threats
from each nutrient element. Unlike nitrogen, the phosphorus cycle has only a negligible
atmospheric component, and phosphorus compounds tend to be associated much
more strongly with soils and sediments. Consequently, land use and disturbance are
important factors controlling the distribution of phosphorus in terrestrial ecosystems.
This study examined soil phosphorus levels in New Hanover County from several
perspectives in order to evaluate the nature of non-point phosphorus sources. The
principal hypothesis addressed was that different land uses are associated with
different concentrations of phosphorus in the soil. High soil phosphorus (“soil-P”) levels are linked with higher loadings of phosphorus to surface and ground waters by erosion
and leaching (Pote et al., 1996; Liu et al., 1997; Sharpley and Tunney, 2000), so soil-P
levels are one indicator of the potential for non-point phosphorus pollution. Other
factors, such as soil type, land management practices, proximity to surface waters, and
slope, are also important, but soil-P levels have been widely measured, so an excellent data base already exists on which to base more focused comparisons. This study
included sampling for soil-P analyses of various land use types in the Bradley Creek
drainage basin in New Hanover County as well as examination of soil-P data and
fertilizer shipment data for the County during the last two decades. A broader data base
of soil-P concentrations in eastern North Carolina was also examined.
Methods
Soil samples were collected from a variety of land use types or habitats in the
Bradley Creek drainage basin between May and September, 2001. Particular efforts
were made to sample major habitat types, such as forests, disturbed land (i.e., ground
cover recently removed), and grassed areas, as well as drainage features linking the
landscape with surface waters, such as detention ponds, drainage swales, and streams.
Soil samples were collected in accordance with instructions from the N.C.
Agronomy Division, which provides soil analysis services through the N.C. Cooperative
Extension. At each sampling location several replicate soil samples were taken by digging to a depth of 2-4” (5-10 cm), mixed in a bucket, then sub-sampled for
placement in a single labeled soil sample container. In the case of aquatic sediment
samples, samples were first dried at 50o C. Samples were then turned in to N.C.
Cooperative Extension, which forwarded them for analysis to the N.C. Agronomy
Division Soil Testing Laboratory. The Division mailed back reports in addition to posting results on the web (http://www.agronomy.agr.state.nc.us).
The N.C. Agronomy Division employs widely used soil extraction and analysis
methods, the Mehlich III extraction followed by atomic absorption spectrometry, to
measure soil-P levels (method described at: http://www.agr.state.nc.us/agronomi/meh3.htm) (Tucker et al., 1997). The Mehlich III
method is considered to extract “plant-available’ phosphorus compounds, providing a
useful measure of phosphorus concentrations relative to plant needs (N.C. Cooperative
Extension Service, 1997). Results are reported using a Phosphorus Index (P-I) system,
which scales soil-P levels in terms of plant needs. P-I values can be converted into concentration units, such as mg P kg-1 or pounds P acre-1, using appropriate factors. P-I
values in the range 0-10 are considered very low, 11-25 are low, 26-50 are moderate,
51-100 are high, and >100 are very high. At P-I values below 50, additional phosphorus
fertilization will generally stimulate a positive plant response. P-I values above 100 (=
213.8 lbs acre-1) are considered excessive and are thought to indicate an increased risk of P export and water pollution.
The N.C. Agronomy Division maintains a public database of soil test data. Soil P-
I data for New Hanover County were obtained for the years 1980-2001, broken down by
crop or land use type. Additional data for other coastal counties were obtained for a regional investigation of soil P-I patterns.
The N.C. Dept. of Agriculture collected data on fertilizer shipments by county
until 1997, when the legislature abolished this reporting requirement. Fertilizer shipment
data for New Hanover County were obtained from the N.C. Dept. of Agriculture’s Agricultural Statistics yearbooks for the period 1982-1997.
Results and Discussion
A total of 100 soil samples were collected from throughout the Bradley Creek
drainage basin, encompassing various developed, disturbed, and undeveloped
habitats. A substantial number (44) of samples were taken in and around detention ponds, drainage swales, and streams.
Soil P-I values were generally in the high range for grassed habitats, low to
moderate for habitats associated with drainage systems, and very low for undisturbed
pine forest (Fig. 1). The moderate P-I values found in swales, stream channels, and pond outlets and basins, in contrast to the generally low and very low values in forested
and disturbed land, suggest that the phosphorus in these drainage systems probably
comes from adjacent high soil-P habitats. Furthermore, the low and very low P-I values
(well below the optimal index value of 50) found in undisturbed pine and hardwood
forests and disturbed land suggest strongly that fertilizer application must be responsible for the higher soil P-I values found in grassed areas.
Summary soil P-I data for New Hanover County show that excessive soil P-I
levels (> P-I of 100) are most often associated with “home grounds” (residential habitats
including gardens, ornamental trees and shrubbery, but most often lawns), with turf (e.g., golf courses) and miscellaneous other crop or land use types accounting for much
lower fractions of the total (Fig 2). These data parallel the pattern observed in the
samples collected from the Bradley Creek drainage. Data for the period 1980-2001
show a variable but statistically significant increase in the numbers of soil samples with
excessive soil P-I values during this period, when development of New Hanover County has been rapid. However, the frequency of excessive soil P-I values reported for New
Hanover County has declined from 52.7% of all samples in the period 1980-1981 to
35.0% in 1990-1991, and to 30.8% in 2000-2001. Thus, even though population and
associated residential development has increased in the county, the frequency of
excess soil P-I levels has declined. In contrast, data for 39 NC Coastal Plain counties, including New Hanover County, show a decline from 53.2% in 1980-1981 to 40.3% in
1990-1991 with an increase to 49.0% in 2000-2001.
The contrasting patterns of increasing numbers of excessive soil P-I values
during a period when the overall frequency of excessive values declined may be
explained in several ways. New residential development of previously undisturbed land with low initial P-I values might generate larger numbers of soil samples with low P-I
values even as ongoing fertilization generates higher P-I values from areas with older,
established lawns and turf. Simple variability in soil testing practices can not be ruled
out, however.
Development in New Hanover County has reduced agricultural land uses while
increasing residential land uses, so it might be expected that declines in fertilizer use by
agriculture might drive an overall reduction in fertilizer use. However, data on crop
acreage and fertilizer shipments for the period 1982-1997 show that as agricultural land
uses declined approximately 5-fold during this period, there was no matching decline in fertilizer shipments (Fig. 3). The fertilizer data show substantial inter-annual variation,
which remains to be explained, but lack of correlation with agricultural production
suggests that residential use of fertilizer is the main factor driving total fertilizer consumption in New Hanover County.
Fertilizer applications are probably responsible for a significant fraction of the P
content of soils in New Hanover County. First, soils in areas impacted by human uses
have much higher soil P contents than soils in undisturbed habitats, suggesting significant fertilizer applications and P accumulation. Second, simple (admittedly,
perhaps simplistic) calculations show that annual fertilizer shipments can represent a
significant portion of the total P content of the county’s soils. The average soil P-I value
measured in this study (assumed for the sake of this calculation to be representative) is
27.7, which converts to 59.3 lb P acre-1. The total area of the county is 849 km2 or 209,792 acres, yielding a total soil P content (for the topmost, sampled layer) of
approximately 6200 tons P in the entire county. Mean annual fertilizer shipments to the
county were 9850 tons. Assuming 10% P2O5 and P=0.436 x P2O5, mean annual
fertilizer P shipments were 430 tons, about 7% of the total soil P content. If a
“background” level of soil P is assumed to be approximately equal to the soil P content of undisturbed forest (mean P-I = 7.1), then the soil P content added by fertilization
would have required about 11 years to accumulate at average fertilizer shipment rates.
It might also be expected that the substantial variation in fertilizer shipments
observed during the period 1982-1997 would drive correlated changes in soil P-I levels (assuming “shipped” fertilizer is actually applied in the county). However, no such
correlation is observed (Fig. 4), suggesting either that assumptions about fertilizer
application do not hold or that applied fertilizer does not accumulate in the county’s
soils. In the latter case, given that the major land use in New Hanover County is not
agricultural but residential, crop removal is an unlikely explanation for lack of soil P accumulation, leaving the possibility that fertilizer-derived P is leaching and/or eroding
from areas where it is applied. If average soil P levels in the county’s soils are
approximately constant over time, then yearly fertilizer P shipments must approximately
balance P loss rates. If cropping and removal of agricultural products is negligible, then
the primary loss mode for land-applied fertilizer P is some combination of soil erosion, runoff, and leaching.
Two sets of data support the idea that fertilizer P is rapidly exported from New
Hanover County landscapes. First, the soil P data collected from the Bradley Creek
drainage show P enrichment in habitats associated with drainage (relative to undeveloped forests or disturbed land), but which otherwise should receive little or no
direct fertilizer P inputs. This pattern suggests transport of P from more heavily fertilized
habitats into the drainage system. Second, nutrient data from the New Hanover County
Tidal Creeks project show that average nutrient levels in the tidal creeks rose
substantially in FY 1996, a year when very high fertilizer shipments to the county occurred, vs. FY 1995 (Fig. 3, Table 1).
Table 1. Mean concentrations of soluble reactive phosphate (ug/liter) for FY95 (July,
1994-June, 1995) and FY96 (July, 1995-June, 1996) for New Hanover County Creeks. Data from NHC Tidal Creeks Program.
_____________________________________________________________________
Creek FY95 FY96
Bradley 3.8 5.1 Futch 2.6 12.6
Hewletts 5.0 7.9
Howe 3.9 4.2
Pages 4.0 7.5
These data indicate that fertilizer use in New Hanover County is coupled to non-
point source nutrient loading and to nutrient levels in the county’s tidal creeks. Given that most fertilizer use appears to be associated with residential applications, efforts to
manage nutrient loading must target homeowners and their use of fertilizers in
particular.
Maintenance of lawns in this area, with its typically sandy soils that normally do not support thick, grassy vegetation, requires both fertilization and watering throughout
the growing season. This combination of nutrient and water loading to sandy soils likely
generates P export far in excess of natural levels, thus driving substantial increases in
nutrient loading to receiving waters. Although refinement of fertilizer application and
watering practices may improve the situation, one must question the effort to create and maintain such large amounts of nutrient-intensive landscape if water quality protection
is a priority.
References Cited
Liu, F., C.C. Mitchell, D.T. Hill, J.W. Odom, and E.W. Rochester. 1997. Phosphorus
recovery in surface runoff from swine lagoon effluent by overland flow. J. Environ.
Qual. 26:995-1001.
N.C. Cooperative Extension Service. 1997. Certification training for Operators of animal
waste management systems – Type A. N.C. Cooperative Extension Service, N.C.
State Univ., Raleigh, N.C.
Pote, D.H., T.C. Daniel, A.N. Sharpley, P.A. Moore, Jr., D.R. Edwards, and D.J. Nichols. 1996. Relating extractable soil phosphorus to phosphorus losses in runoff.
Soil Sci. Soc. Am. J. 60:855-859.
Sharpley, A., and H. Tunney. 2000. Phosphorus research strategies to meet agricultural
and environmental challenges of the 21st century. J. Environ. Qual. 29:176-181.
Tucker, M.R., J.K. Messick, and C.C. Carter. 1997. Crop fertilization based on North
Carolina soil tests. N.C. Dept. of Agriculture & Consumer Services, Raleigh, N.C. 81
pp.
Figure Legends
Fig. 1. Results of soil testing for habitats in the Bradley Creek drainage basin.
Fig. 2. The yearly number of soil samples from New Hanover County with excessive soil
P-I values (> P-I = 100) by land use type, 1980-2001. The number of total samples with
excessive P-I values increases significantly with time (F=5.56, df= 1,20, P=0.0287,
r2=0.217).
Fig. 3. Agricultural crop acres harvested and fertilizer shipments in New Hanover
County, 1982-1997.
Fig. 4. Plot of the number of excessive soil P-I values vs. fertilizer shipments in New
Hanover County, 1982-1997. There is no significant correlation (F=0.77, df=1,14, P=0.395, r2=0.05).
16.0 Studies of Oyster Reefs in New Hanover County Tidal Creeks
by
Martin Posey, Troy Alphin, Jacqueline Horner, Bethany Noller
Center for Marine Science
University of North Carolina at Wilmington Wilmington, NC 28409
I. Overview
Oyster reefs are a critical part of a tidal creek ecosystem, biologically, chemically, and physically. In conjunction with funding and support from North Carolina Sea Grant,
the UNCW Center for Marine Science, and the UNCW Benthic Ecology Laboratory, the
New Hanover County Tidal Creeks Program has partially supported three projects
examining oyster communities and their ecosystem effects in New Hanover County tidal
creeks. The largest of these projects is summarized in Chapter 17 (Nelson, Leonard, Alphin, Posey, Mallin, and Parsons) and examines the effectiveness of a constructed
oyster reef on reducing concentrations of water column nutrients, suspended solids,
and chlorophyll a. The second project utilizes aerial surveys to measure percent cover
and total cover of oysters in lower Pages, Hewletts, Howe and Whiskey Creeks. This
project is ongoing and will require some additional flyovers as well as photographic data analysis to complete. It will be reported on next year. The final project, summarized in this chapter, examines some of the morphological characteristics of the oyster reefs
themselves. In particular, this project concentrates on aspects of reef structural
complexity, uniformity and oyster density that may influence their role as habitat and
their ecosystem function. Physical characteristics of the reefs may play an important role in determining the degree to which oysters can influence water quality and maintain habitat function, although these two aspects may not always be complementary.
Characteristics of oyster reef morphology may provide a better metric to evaluate
ecosystem health than simple measurements of reef coverage.
II. Background
Oysters have long been recognized as an important shellfish resource, though
oyster populations have suffered dramatic declines over the past several decades in
much of their range (Hargis 1999, Breitberg et al. 2000, Mann 2000). However, researchers and resource managers have only recently begun to understand the importance of oyster reefs as a critical habitat. Oysters provide refuge and forage area
for certain decapods and fish, and have broad ecosystem effects through their filtration
of the overlying water (Ulanowicz and Tuttle 1992, Coen et al. 1999b). In general,
oyster reefs are a highly productive feature of the estuary that provide more to the local communities than the simple market value of the harvested oysters. Throughout much of their range, oysters constitute an expansive habitat in estuaries and sounds. In the
Chesapeake Bay and Pamlico Sound systems, subtidal oyster beds have historically
covered a significant proportion of the bottom (Newell 1988, Hargis 1999, Lenihan
1999, Mann 2000) and are recognized as an essential fisheries habitat (Coen et al.
1999b). Intertidal oyster beds are also present in portions of the Pamlico system and lower Chesapeake Bay (O’Beirn et al 2000). From southern Pamlico Sound southward
through the southeastern United States and into the Gulf coast of Florida, oysters are
abundant intertidally and into the shallow subtidal (Kennedy and Sanford 1999) and
may cover greater than 50% of the mid intertidal in some coastal creeks and sounds
(Powell et al. 1995, Posey et. al. 1999, Grizzle and Castagna 2000, Meyer and Townsend 2000). Because of a lack of seagrass beds from southeastern North
Carolina to northern Florida, oysters represent the dominant structural habitat in the mid
intertidal to shallow subtidal regions along those coasts.
The potential ecosystem and economic importance of oyster reefs as habitat involves both effects on smaller prey species as well as indirect and direct effects on
larger fish and decapods. The presence of a structural refuge has been shown to
reduce predation on smaller fish and invertebrates and is often associated with higher
faunal abundances (Peterson 1979). The shell matrix of oyster reefs provides refuge
habitat for species living on the sediment surface or among the shells, including several species of fish, crabs, shrimp and other small crustaceans (Larsen 1985, Castel et al.
1989, Meyer 1994, Breitburg 1999, Posey et al. 1999, Coen et al. 1999b). The shells
also provide hard substrate for the attachment of species such as sponges. Elevated
densities of panaeid shrimp, grass shrimp, xanthid and blue crabs, and bottom-oriented
fish have been noted in some reefs (Wilber and Herrnkind 1986, Meyer 1994, Breitburg et al. 1995, Eggleston et al. 1998, Coen and Luckenbach 2000, Harding and Mann
2000). Effects on species burrowing into the sediment are more variable. Some studies
have shown enhanced infaunal abundance or biomass within or adjacent to oyster
reefs (Castel et al 1989, Larsen 1985), while other studies have indicated lower infaunal
abundances under certain conditions (Powell 1994, Iribarne 1996), possibly reflecting indirect trophic effects. Consequences of enhanced invertebrate populations for
commercially and recreationally important species may be simple direct effects of
increased available food resources (Luckenbach et al. 2000) or more complex indirect
effects as sources of larvae that enhance prey recruitment to adjacent areas. Oyster
reefs may serve as protected source habitats helping to support prey that then venture or recruit into open sandflats where predatory fish and crabs have greater access.
These indirect effects may be particularly important in southeastern North Carolina
where benthic infaunal populations show dramatic declines and refuges such as oyster
reefs may serve as important source areas for the general community. Enhancement
of epifauna and infauna may not only occur from increased refuge, but may also result from greater food availability. Oysters remove particulates from the overlying water and
deposit material as feces or psuedofeces that tend to be high in organic content and
are likely associated with locally enhanced nitrogen levels (Dame and Libes 1993).
Locally enhanced nutrients or organics may stimulate bacterial and benthic microalgal
production as well as other deposit feeder resources.
Subtidal reefs may serve as permanent forage sites for species such as striped
bass, weakfish and bluefish (Harding and Mann 1999). Many commercially important
species, such as blue crabs, panaeid shrimp, striped bass, sheepshead, and flounder,
utilize intertidal oyster reefs as transients, coming and going with the tide (Posey et al. 1999, Coen et al. 1999b). For species not resident on oyster reefs, these habitats may
provide important ephemeral foraging areas or refuges, with many fish and decapods
moving into shallow water to feed as the water covers the tideflat. Intertidal reefs in the Chesapeake Bay and South Carolina are characterized by higher densities of transient
fish such as pinfish, bluefish, blue crabs and seabass compared to adjacent open areas
(O’Beirn et al. 2000, Coen et al. 1999a). Diver observations of a tideflat region in
southeastern North Carolina indicated greater densities of fish moving onto the edge of
oyster reefs and feeding along the edge of those reefs compared to adjacent unstructured tideflat areas (Powell 1994, Posey et al. 1999).
The habitat value of oyster reef patches lies not only in the use of single reef
patches, but also in their potential role as part of a series of habitats in a larger system.
When combined with other structural habitats and/or present in a series of patches, subtidal reefs may enhance movement of fish across estuarine or sound systems
(Breitburg et al. 2000). In such instances, a given individual may utilize a specific oyster
patch for only a short period, but may move between oyster patches or among oyster,
seagrass, marsh or debris patches on a regular basis utilizing different food resources.
On a smaller scale, a combination of oyster and seagrass patches was shown to enhance the foraging extent and possibly increase the accessibility of clam prey
resources for blue crabs foraging in a North Carolina system (Micheli and Peterson
1999). In this case, the location of several habitat types in proximity was associated
with greater foraging extent, probably related to greater protection from bird predators.
Similarly, oyster reefs may provide refuge for only certain life stages, but their presence may have important population implications (Ray 1997) and restoration of reefs in some
areas may augment juvenile fish production (Grabowski et al. 2000).
Aside from their role as habitat, oysters may also have important ecosystem
functions through their high filtering capability. Their high filtration rates and ability to remove particulates has led to the suggestion that oyster reefs may significantly impact
water quality, at least at historically high densities (Ulanowicz and Tuttle 1992, Dame
and Libes 1993, Mann 2000). Some researchers have suggested that oysters may
have significantly reduced the concentrations of suspended particulates, water column
chlorophyll and water column nutrients before reefs were decimated by disease and overharvesting. Recent efforts have concentrated on re-establishing oyster reefs in
areas where they have been historically present (and where anthropogenic pressures
have now lessened). Several state and local governments have begun oyster
restoration programs with the specific objective of improving coastal water quality.
Although there is growing data indicating the potential ecosystem and fisheries
habitat roles of oyster reefs, the function of oyster reefs appears to vary with landscape
characteristics. Critical characteristics of oyster reefs that may affect their habitat
functions include shell cover within a reef, vertical complexity within the bed, vertical
relief, and edge characteristics (Breitburg 1999, Lenihan 1999, Griffitt et al. 1999, O’Biern et al. 2000). Greater vertical complexity (presence of a mix of high relief and
low relief areas) and vertical relief may provide greater quality habitat for fish and
decapods utilizing the reef as refuge. Greater density of live oyster, larger oysters and
greater vertical relief are among the reef architecture factors that may enhance water
quality effects (enhance removal of material from the water flowing over a reef). In this project, we assessed the following reef characteristics on a per reef basis in Pages,
Howe, Hewletts and Whiskey Creeks: % shell cover within a reef (relates to complexity
of the shell habitat), occurrence of shell hash, or broken shell material (habitat complexity), density of live oysters, and vertical relief of shells (maximum height above
the underlying substrate).
III. Methods
Two or three intertidal oyster reefs were randomly selected in the lower portions
of Pages, Howe, Hewletts and Whiskey Creeks. All reefs selected were at least 3m in
diameter and areas that were obviously disturbed by proximity to marinas, channels,
etc. were avoided.
Percent shell cover, presence of shell hash, and number of live oysters were
measured in replicate 30 cm x 30 cm quadrats. Ten quadrat samples were taken within
each of the selected reefs. Percent oyster cover was determined by the point intercept
method. Five monofilament lines were strung at right angles over the quadrat creating
20 intersecting points. The presence or absence of shell under each point was then noted. Shell hash was defined as broken shell matrix underlying live shell or shell
culms. Shell hash may be important habitat for cryptic fish, crabs and shrimp. A
quadrat was qualitatively recorded as having shell hash if there was greater than 10%
of the underlying area covered. The number of live oysters in each of these quadrats
was also recorded. Culms were not destroyed (broken apart) in this process, so there is some possibility that the complexity of culm (groups of connected upright oyster
shells) structure may have led to some undercounting of new recruits.
Vertical relief of the oyster bed was defined in this study as the height of shells
(culms) above the underlying sand substrate. Ten 50 cm X 50 cm quadrats were selected on each reef. The vertical height of shell underlying each of 16 points created
by intersecting lines on the quadrats was recorded, measuring from the sand substrate
to the highest point within 1 cm diameter of the intersection point.
IV. Results
Percent shell cover within reefs varied among creeks. Reefs within Pages Creek
had the highest cover of shell, with 92.5% of the reef surface area having shell (Figure
1). Both Howe and Hewletts Creeks had intermediate levels of shell cover, with 69.3%
of the reef area actually covered by shell in Howe Creek and 75.8% shell cover for reefs in Hewletts Creek (Figure 1). Reefs within Whiskey Creek were more variable, having
large amounts of open sand patches within the reefs. Whiskey Creek oyster reefs had
only 52.9% actual shell cover within the definable reef areas. Shell hash presence did
not strictly correlate with overall shell cover. Greatest shell hash was observed in
Hewletts Creek, with 50% of quadrats having 10% or more shell hash present. This was followed by Howe (40%), Pages (30%), and Whiskey (21%) Creeks (Figure 1).
Densities of live oysters were greatest in Pages and Hewletts Creeks (Figure 2)
and least in Howe and Whiskey Creeks. The densities for Pages and Hewletts Creeks
are low but comparable to that observed in other southeastern North Carolina marine intertidal areas (T. Alphin and M. Posey, personal observation). The densities in
Whiskey and Howe Creeks are lower than we have observed in other areas of
Masonboro Sound and areas between Pages Creek and the New River (Alphin and Posey, personal observation). These low densities may reflect low recruitment and/or
high mortality. However, in a preliminary study we conducted in 1995, we observed
high mortality of oyster spat transplanted to Howe and Hewletts Creeks relative to
Pages Creek (unpublished data). Pages Creek was also characterized by high
variability in density of live oyster among quadrats.
Vertical relief of oyster reefs was greatest in Howe Creek (Figure 3) and
intermediate in Pages Creek. Average vertical relief was low in both Hewletts and
Whiskey Creeks. Vertical relief represents the greatest height of oysters above the
substrate and not average reef height. As such, it is a measure of the presence of well-developed oyster culms and possibly represents greater surface complexity.
V. Conclusions
These results suggest considerable variability in oyster reef characteristics among the various New Hanover tidal creeks examined. Pages Creek was
distinguished by high shell coverage, relatively high densities of live oysters (compared
to other creeks examined), and intermediate vertical relief. The reefs in this creek have
a generally well-developed physical structure and appear to support significant oyster
densities. Though reefs may cover a large percent of the overall area of Whiskey Creek (ongoing analyses), these reefs are poorly developed with respect to physical
structure and support low densities of live oysters. The Whiskey Creek oyster reefs
may reflect the influence of stress from disease, siltation, or other factors affecting
survival and growth of oysters. Howe and Hewletts Creeks exhibit intermediate
patterns. Howe Creek has intermediate shell cover within reefs and high vertical relief, but low live oyster density within reefs. This may reflect recent mortality or low
recruitment set combined with persistence of shells from dead individuals. Hewletts
Creek had relatively high live oyster densities, but low relief. This suggests that most
oysters are smaller (size measurements are planned for an upcoming survey) or reefs
have a flatter profile due to disturbance, harvesting, or tideflat topography. Our goals over the coming year, as we finish analysis of morphology and coverage, will be to
evaluate how the different functions of oysters reefs (habitat, water quality, larval
sources, and human use) affect and are affected by these characteristics. By
combining planned experimental studies with assessment of natural reef patterns, we
hope to eventually develop an understanding of how oysters may differentially affect communities in the various tidal creek systems.
VI. Literature Cited
Breitburg, D.L. 1999. Are three-dimensional structure and healthy oyster populations
keys to an ecologically interesting and important fish community? P. 239-250. In:
M.W. Luckenbach, R. Mann and J.A. Wesson (eds.), Oyster reef habitat restoration:
A synopsis and synthesis of approaches. Virginia Institute of Marine Science Press.
Breitburg, D.L., L.D. Coen, M.W. Luckenbach, R. Mann, M. Posey and J. Wesson.
2000. Oyster reef restoration: convergence of harvest and conservation strategies.
Journal of Shellfish Research 19:371-378.
Breitburg, D.L., M.A. Palmer and T. Loher. 1995. Larval distributions and the spatial
patterns of settlement of an oyster reef fish: Responses to flow. 1995. Marine
Ecology Progress Series 125:45-60.
Castel, J., P-J. Labourg, V. Escaravage, I. Auby and M.E. Garcia. 1989. Influence of seagrass beds and oyster parks on the abundance and biomass patterns of meio-
and macrobenthos in tidal flats. Estuarine, Coastal and Shelf Science 28:71-85.
Coen, L.D. and M.W. Luckenbach. 2000. Developing success criteria and goals for
evaluating oyster reef restoration: Ecological function or resource exploitation? Ecological Engineering 15:323-343.
Coen, L.D., D.M. Knott, E.L. Wenner, N.H. Hadley, A.H. Ringwood and M.Y. Bobo.
1999a. Intertidal oyster reef studies in South Carolina: design, sampling and
experimental focus for evaluating habitat value and function. Pp. 133-158. In: M.W. Luckenbach, R. Mann and J.A. Wesson (eds.), Oyster reef habitat restoration: A
synopsis and synthesis of approaches. Virginia Institute of Marine Science Press.
Coen, L.D., M.W. Luckenbach and D.L. Breitburg. 1999b. The role of oyster reefs as
essential fish habitat: a review of current knowledge andsome new perspectives. American Fisheries Society Symposium, Vol. 22:438-454.
Dame, R. and S. Libes. 1993. Oyster reefs and nutrient retention in tidal creeks. Journal
of experimental Marine Biology and Ecology. 171:251-258.
Eggleston, D.B., L.L. Etherington and W.E. Elis. 1998. Organism response to benthic
habitat patchiness: species and habitat-dependent recruitment of decapod
crustaceans. Journal of experimental Marine Biology and Ecology 223:111-132.
Grabowski, J.H., C.H. Peterson, M.A. Dolan, A.R. Hughes and D.L. Kimbro. 2000. Evaluation of the effectiveness of restoring oyster reef habitat: An integrated
approach. Report submitted to the North Carolina National Estuarine Research
Reserve.
Griffitt, J., M. Posey and T. Alphin. 1999. Effects of edge fragmentation on oyster reef utilization by transient nekton. The Journal of the Elisha Mitchell Scientific Society
115:98-103.
Grizzle, R. and M. Castagna. 2000. Natural intertidal reefs in Florida: Can they teach us
anything about constructed/restored reefs? Journal of Shellfish Research 19:609.
Harding, J.M. and R. Mann. 2000. Estimates of naked goby (Gobiosoma bosc), striped
blenny (Chasmodes bosquianus) and eastern oyster (Crassostrea virginica) larval
production around a restored Chesapeake Bay oyster reef. Bulletin of Marine Science 66:29-45.
Hargis, W.J., Jr. 1999. The evolution of the Chesapeake oyster reef system during the
Holocene epoch. Pp. 5-23, In: M.W. Luckenbach, R. Mann and J.A. Wesson (eds.),
Oyster reef habitat restoration: A synopsis and synthesis of approaches. Virginia Institute of Marine Science Press.
Iribarne, O. 1996. Habitat structure, population abundance and the opportunity for
selection on body weight in the amphipod Eogammarus oclairri. Marine Biology
127:143-150.
Kennedy, V.S. and L.P. Sanford. 1999. Characteristics of relatively unexploited beds of
the eastern oyster, Crassostrea virginica, and early restoration programs. Pp. 25-46.
In: M.W. Luckenbach, R. Mann and J.A. Wesson (eds.), Oyster reef habitat
restoration: A synopsis and synthesis of approaches. Virginia Institute of Marine
Science Press. Larsen, P.F. 1985. The benthic macrofauna associated with the oyster reefs of the
James River estuary, U.S.A. Int. Rev. Gesamt. Hydrobiol. 70:797-814.
Lenihan, H.S. 1999. Physical-biological coupling on oyster reefs: how habitat structure influences individual performance. Ecological Monographs 69:251-275.
Luckenbach, M., F. O’Beirn, J. Harding, R. Mann and J. Nestlerode. 2000. Temporal
patterns of fish and decapod utilization of oyster reefs: comparisons across an
estuarine gradient. Journal of Shellfish Research 19:610. Mann, R. 2000. Restoring the oyster reef communities in the Chesapeake Bay: A
commentary. Journal of Shellfish Research 19:335-340.
Meyer, D.L. 1994. Habitat partitioning between the xanthid crabs Panopeus herbstii and
Eurypanopeus depressus on intertidal oyster reefs (Crassostrea virginica) in
southeastern North Carolina. Estuaries 17:674-679.
Meyer, D.L. and E.C. Townsend. 2000. Faunal utilization of intertidal eastern oyster
(Crassostrea virginica) reefs in the southeastern United States. Estuaries 23:34-45.
Micheli, F. and C.H. Peterson. 1999. Estuarine vegetated habitats as corridors for predator movements. Conservation Biology 13:869-881.
Newell, R.I.E. 1988. Ecological changes in the Chesapeake Bay: are they the result of
overharvesting the American oyster, Crassostrea virginica? Pp. 536-546, In: M.P.
Lynch & E.C. Krome (eds.). Understanding the Estuary: Advances in Chesapeake Bay Research. Chesapeake Research Consortium, Publication 129 CBT/TRS 24/88,
Gloucester Point, Va.
O’Beirn, F.X., M.W. Luckenbach, J.A. Nestlerode and G.M. Coates. 2000. Toward
design criteria in constructed oyster reefs: Oyster recruitment as a function of substrate type and tidal height. Journal of Shellfish Research 19:387-395.
Peterson, C.H. 1979. Predation, competition, exclusion and diversity in the soft-sediment benthic communities of estuaries and lagoons. Pp. 233-264 In: R.J. Livingston (ed), Ecological processes in coastal and marine systems. Plenum Press, New York.
Posey, M.H., T.D. Alphin, C.M. Powell and E. Townsend. 1999. Use of oyster reefs as
habitat for epibenthic fish and decapods. Pp. 229-237. In: M.W. Luckenbach, R.
Mann and J.A. Wesson (eds.), Oyster reef habitat restoration: A synopsis and synthesis of approaches. Virginia Institute of Marine Science Press.
Powell, C.M. 1994. Trophic linkages between intertidal oyster reefs and their adjacent
sandflat communities. M.S. Thesis. University of North Carolina at Wilmington. 46
pp.
Powell, E.N., J. Song, M.S. Ellis and E.A. Wilson-Ormond. 1995. The status of long-
term trends of oyster reefs in Galveston Bay. Journal of Shellfish Research 14:429-
457.
Ray, G.S. 1997. Do the metapopulation dynamics of estuarine fishes influence the
stability of shelf ecosystems? Bulletin of Marine Science 60:1040-1049.
Ulanowicz, R.E. and J.H. Tuttle. 1992. The trophic consequences of oyster stock
rehabilitation in Chesapeake Bay. Estuaries 15:298-306.
Wilbur, D.H. and W.F. Herrnkind. 1986. The fall emigration of stone crabs Menippe
mercenaria (Say) from an intertidal oyster habitat and temperature’s effect on
locomotory activity. Journal of experimental Marine Biology and Ecology 102: 209-
221.
17.0 Created Oyster (Crassostrea virginica) Reefs as Self-Sustaining Mechanisms for
Water Quality Improvements in Small Tidal Creeks:
A Pilot Study
by
Kim A. Nelson, Lynn A. Leonard, Martin H. Posey, Troy D. Alphin,
Michael A. Mallin, and Douglas C. Parsons
Center for Marine Science
University of North Carolina at Wilmington
INTRODUCTION
Recent increases in coastal development are exerting previously unrealized
pressures on shrinking natural resources. Each year, coastal waters are subject to
higher and higher levels of runoff with increased nutrient and sediment loading. The net result is that coastal waters and local environs suffer from widespread habitat
degradation, declining water quality, closure of waters to shellfishing, and quotas placed
on many critical fisheries. Some studies suggest that water quality is affected not only
by the inputs entering a system, but also by the biological and hydrodynamic processes
that help the system naturally remove these contaminants (Harsh & Luckenbach, 2000). Filter-feeding bivalves such as the eastern oyster, Crassostrea virginica, are
currently being investigated as bioremediation tools to reduce contaminant loading in
marsh-estuarine systems (Breitburg et al., 2000). At present, however, insufficient data
exist to assess whether these efforts will restore water quality in degraded
environments.
Regarded as a “key marine ecosystem” (Jackson et al., 2001), oyster reefs have
been shown to strongly influence estuarine habitats by altering physical and biological
parameters within the associated system (Dame et al., 2000; Mann 2000; Lenihan,
1999). The oyster is a filter feeder, removing large quantities of seston (suspended material) from the overlying water column, thereby reducing the amount of suspended
sediment, detritus and nutrient levels in marine and estuarine systems (Brambaugh et
al., 2000; Gerritson et al., 1994; Mann, 2000). In addition, the biogenic structure of
oyster reef communities may alter hydrodynamic conditions, further facilitating the
removal of particulate matter and increasing water quality (Lenihan, 1999; Meyer & Townsend, 2000). These factors reduce the risk of eutrophication, while improving
water clarity and increasing the aesthetic appeal of estuarine systems.
Based on potential benefits, oyster restoration programs are being considered by
various state agencies as an integral aspect of estuarine bio-remediation efforts (Breitburg et al., 2000). Large-scale restoration projects are being conducted in the
Maryland and Virginia; while North Carolina has recently increased spending on
shellfish related studies in association with water quality improvements. This study
examines the effects of created oyster (Crassostrea virginica) reefs on suspended
particulate matter, chlorophyll a, and ammonium concentrations downstream of the reef
in a small tributary tidal creek. The study also addresses how reef placement and reef
size affect both flow hydrodynamics and selected water quality parameters within a small tributary system.
STUDY AREA
This study was conducted in Hewletts Creek (34°10′N latitude, 77°55′W
longitude), a moderately-impacted, incised mainland creek located within the North
Carolina Coastal Plain in New Hanover County, near the city of Wilmington (Figure 1).
The site is located in a small tributary channel approximately 3-5 m wide and 1-2 m
deep at high tide within 0.5 km of the mouth of Hewletts Creek. Tides are low mesotidal (mean tidal range of 1.2m) and semidiurnal with a strong diurnal inequality.
The nershore has significant stands of Spartina alterniflora, and the sediments are
dominated by fine silt and clay.
METHODS
Experimental Design: The study site consists of one channel occupied by a constructed reef and an adjacent control channel that did not have a reef. A reef measuring 2m X
3m was established in September 2000. In May 2001, the reef was enlarged to 3m X
4m to span the entire creek width. Except for natural growth and recruitment, vertical
height was not altered during reef addition. The reef was constructed through the
movement of live oysters from adjacent areas. The reef was constructed of 1 m2 PVC frames covered by hardware cloth to form the foundation on which oysters were placed.
Density of oysters within the reef reflected an ambient high oyster density of 125
oysters per m2. A subset of the oysters placed within the reef were marked and
subsequently attached to the reef foundation (to facilitate recovery). Oyster densities
were monitored once every ten weeks. When necessary, additional oysters were placed within the reef to maintain the target density of 125 oysters per m2. Every six
months, the grids were retrieved from the bottom of the creek. Growth and mortality
measurements were taken using the marked oysters attached to the grid. Growth
measurements, length and width, were taken on live oysters only.
Water quality parameters were measured 0.05 m upstream and downstream of
the reef. Additional samples were collected at the control site (without reef) for
comparison. Preliminary measurements were collected prior to reef placement, with
subsequent collections each month for one year. All data were collected during the
peak flow of ebbing tides (~ one hour after high tide) and every hour for the following three hours. The overall sampling design allowed for observation of changes in water
quality parameters related to flow speed, water level and season. All data were
collected on days with a predicted tidal range of 0.9 to 1.1 m to decrease sampling bias
resulting from differences in tidal amplitude.
Sampling Methods: Water column particulate concentrations were measured by the
collection of two, 1000ml replicate water samples. All samples were collected by hand
to minimize sediment and flow disturbance and to decrease point sampling bias due to
temporal and spatial flow variability. The samples were then filtered through
preweighed 1µm glass fiber filters, dried overnight at 40°C, re-weighed and calculated
in mg l-1. Organic content was determined by combustion at 450° C for 4 hours and
given as a weight percent. In association with the New Hanover County Tidal Creeks Water Quality Program, chlorophyll a was measured from replicate 50ml filtered
samples using Welschmeyer (1994) flourimetric techniques. Ammonium
concentrations were calculated from 25ml duplicate samples according to the methods
of Parsons et al. (1984). Analysis of variance (ANOVA) was used to determine if
particulate concentrations, chlorophyll a, and ammonium rates differed from upstream
to downstream, and to determine if reef sites differed from control sites.
Flow velocities were measured above the reef, below the reef, and at the reef
crest using a Marsh McBirney Flow Mate electromagnetic current meter. Pre-reef data
were collected in August 2000 and comparison data were collected in October 2001
after reef establishment. Hourly flow data were collected approximately 10 cm above the bed during the falling tide at each location. These data were used in conjunction
with measures of water level and channel bathymetry to determine flow discharge
across the reef. Temperature and salinity data were recorded using a Hydrolab
Datasonde. The creeks containing reef and control sites had similar mean temperatures
ranging from 12.5° to 29°C, and mean salinities ranging from 20 to 35ppt.
RESULTS
Reef Characteristics
Immediately following reef placement in August 2000, the mean length and width of individual, viable oysters was 48mm and 30mm, respectively (Figure 2). Four
months later, the target population had increased in size. In December 2001, mean
length increased by ~27% to 61mm and mean width increased by ~7% to
approximately 32mm. These size distributions may be biased because they reflect the
mean of all surviving oysters. If the size increase for all surviving oysters, rather than overall size changes for the whole population is evaluated, oysters grew by an average
of ~4.5mm in length and ~3mm in width. Survivorship over this time period was 79%
(or a mortality rate of 21%). Between December and June, the mean individual length
increased by ~9mm and mean individual width increased by ~4mm. Mortality
decreased by another 23% between December and June yielding a survivorship value of 56% of the original oysters by June 2001.
Flow Data
Current velocities measured upstream, downstream, and over the reef crest
were less than 5 cm s-1 during ebb flow (Figure 3A). Minimum velocities occurred at
high slack water and increased to almost 3 cm s-1 within the first hour of falling water. The lowest velocities observed during ebb tide occurred at three hours after high slack
water. There was little variation in flow velocity between sampling locations, although
velocities measured over the reef from hour 1 to hour 3 were greater than those
simultaneously measured downstream and upstream of the reef. These data suggest
that flows are slightly accelerated as they pass over the reef. Flow discharge (Figure 3B) through the creek channel ranged from about 90 L s-1 to approximately 55 L s-1.
Maximum flow discharge appears to coincide with peak velocities at hour 2, when water
levels are still high. Minimum flow discharge is coincident with minimum tidal current
velocities at hour three.
Suspended Solids
Prior to initial reef placement in September 2001, mean total suspended solids (TSS) concentrations in the study area ranged from 23 mg l-1 to 40 mg l-1 (Figure 4).
There was no significant difference (p<0.05) in TSS concentrations measured above
and below the region where the reef was ultimately located. Following reef placement,
however, TSS concentrations in the treatment channel were substantially less than
concentrations measured in the control channel every month except for August 2001. Statistically significant differences in TSS concentrations measured above and below
the reef were observed only twice during this study: October and February 2000.
However, when significant differences did occur, TSS concentrations below the reef
were always less than those measured upstream of the reef. The additional reef
material emplaced in May 2001 appears to have had little effect on TSS levels. Organic suspended solids did not significantly differ above and below the reef (Figure
5).
Ammonium
The average ebb concentrations (mean of all hourly samples) of ammonium
measured three hours and one hour after high water are shown in Figures 6 and 7.
The highest ammonium concentrations measured during this study (100-120 µg l-1)
occurred in August 2000 prior to reef placement. In September 2000, ammonium
concentrations decreased to approximately 30 µg l-1 in both the "oyster transplant" and control channels, even though the reef had not yet been constructed. For the remainder of the study, including the periods after initial reef placement and reef
enlargement, ammonium concentrations showed little variation between treatment and
control and between upstream and downstream measures.
Mallin et al. (1999) reported significantly higher levels of nutrients (nitrate and phosphate) in area tidal creeks approximately three hours following high water. This
time coincides with the period of minimum discharge at the study site (Figure 3B).
Examination of mean ammonium concentrations taken at hour 3 in both the treated and
control channel (Figure 6) suggests that neither reef placement nor enlargement affected ammonium concentrations during this study.
Chlorophyll a
Mean chlorophyll a concentrations measured during ebb tide ranged from 1 to 4
µg l-1 during this study (Figure 8). Concentrations showed a strong seasonal pattern
where maximum concentrations occurred in the summers prior to and following reef placement, and minimum values were observed in winter. No significant difference was
observed between the treated and control channels, nor in samples collected above
and below the reef through April 2001. Chlorophyll a concentrations measured during
hour 3 (Figure 8) indicate that there was no difference in above-to-below reef
chlorophyll a concentrations until reef enlargement in May 2001. At this time,
chlorophyll a concentrations below the reef decreased substantially below the reef. In addition, there is a significant decrease in chlorophyll a in the creek containing the reef compared to the control location.
DISCUSSION
Recent studies demonstrate that flow velocities >6cm s-1 may exert a negative effect on oyster filtration rates (Harsh & Luckenbach, 2000). These results suggest that
smaller reefs placed in low velocity environments, such as the focus of the current
study, will have high filtration success if not overwhelmed by siltation. Our data indicate
that siltation did not negatively impact the study reefs despite the close proximity of the
study area to adjacent uplands. Oyster mortality (due to siltation or any other possible causes) did not reduce the density of oysters traumatically in any given sampling
period. Consequently, the results of this study indicate that small feeder creeks are, in
fact, excellent locations to employ oyster reefs as remediation tools for water quality
effects.
Our results further indicate that our reef treatment, despite its small size and low
density, can provide an effective mechanism for removing particulates, but suggest that
there may be a concentration threshold beyond which effectiveness is limited by reef
size. Following reef placement in September 2000, average TSS concentrations
showed a slight decrease below the reef during fall and early spring, corresponding with months of highest oyster feeding activity. TSS concentrations measured in the treated
creek were significantly lower than TSS concentrations measured in the control with the
exception of the final measurement taken in August 2001. The lack of difference in late
summer is most likely due to the reef's small size and low density making it difficult for
these organisms to filter enough volume for us to detect a reduction in high background concentrations. Such elevated concentrations typically occur in summer months
(Leonard, 1997) and also following periods of intense rainfall (Mallin et al., 1993) in
Southeastern estuarine systems.
Recent hydrological modeling suggests that intertidal reefs located in shallow tributaries will have a greater impact on filtration capabilities due to an increased ratio of
reef surface area to water volume (Gerritsen et al., 1994). Shallow tidal creeks, such as
the type examined during this study, may increase particulate encounter probabilities,
thereby increasing oyster filtration efficiency (Gerritsen et al., 1994). In addition, small
tributary creeks are the first to receive concentrated levels of runoff and contaminate loading from non-point sources. Means of ammonium and chlorophyll a concentrations
did not show significant differences between treated and control sites when averaged
over the duration of ebb tide. Mallin et al. (1999), however, reported that maximum
concentrations of fecal coliform occur approximately 3-4 hours following high water in
the mainstem of this system. Moreover, chlorophyll a concentrations show an order of
magnitude difference at low tide, with maximum concentrations occurring 3-5 hours following high tide. This is the period of lowest discharge or the time when the ratio of
reef surface area to water volume is maximum. While no difference in ammonium
concentrations between treated and control sites was observed during this time,
ammonium concentrations consistently increased below the reef during hour three
when water volume was low in relation to surface area.
Chlorophyll a measures, while not affected by initial reef placement, were
substantially reduced after May 2001 when the size of the reef was increased to the 3m
X 4m design. This result provides compelling evidence that some water quality
parameters in this system may be significantly affected by the relationship between
water volume and reef surface area. These results suggest that there may be an
optimal reef design that maximizes contaminant removal. In addition, these results provide sound preliminary information on when (seasonally and tidally) this removal is
most effective.
CONCLUSIONS
This work has demonstrated that small viable oyster reefs can be established
and maintained over periods of at least one-year in small upland tidal creek feeder
channels; regions most likely to first feel the effects of contaminant loading from
adjacent uplands. Further, these results suggest that an optimal ratio of reef size to
flow discharge exists whereby the filtration benefits provided by oyster reefs is a maximum. Additional studies are needed to determine the volume to reef ratio and the
reef geometry that would achieve desired results utilizing minimum resources. This
study concludes that placement of a small Crassostrea virginica reef at this site resulted
in:
• increased flow velocity over reef;
• reduced TSS concentrations except during periods of elevated load; and
• decreased chlorophyll a concentration below the reef after increasing reef
size
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Reef Restoration: Convergence of Harvest and Conservation Strategies. Journal of
Shellfish Research 19(1):371-377.
Brambaugh, R.D., L.A. Sorabella, C.O. Garcia, W.J. Goldsborough & J.A.Wesson. 2000. Making a Case for Community-Based Oyster Restoration: An Example from Hampton
Roads, Virginia, USA. Journal of Shellfish Research 19(1):397-400.
Dame, R.D., D. Bushek, D. Allen, D. Edwards, L. Gregory, A. Lewitus. S. Crawford, E.
Koepfler, C. Corbett, B. Kjerfve & T. Prins. 2000. The Experimental Analysis of Tidal Creeks Dominated by Oyster Reefs: The Premanipulation Year. Journal of Shellfish
Research 19(1):361-369.
Gerritsen, J., Holland, A.F. & D.E. Irvine, 1994. Suspension-Feeding Bivalves and the
Fate of the Primary Production: An Estuarine Model Applied to Chesapeake. Estuaries 17(2):403-416.
Harsh, D.A. & M.W. Luckenbach, 2000. Materials Processing by Oysters in Patches:
Interactive Roles of Current Speed and Seston Composition. In: Luckenbach, M.W.,
Mann, R., and J.A. Wesson (Eds.) Oyster Reef Habitat Restoration: A Synopsis and Synthesis of Approaches. Virginia Institute of Marine Science, Williamsburg,
Virginia, 1999.
Jackson, J.B.C., Kirby, M.X., Berger, W.H., Bjorndal, K.A., Botsford, L.W., Bourque, B.J., Bradbury, R.H., Cooke, R., Erlandson, J., Estes, J.A., Hughes, T.P., Kidwell, S.,
Lange, C.B., Lenihan, H.S., Pandolfi, J.M., Peterson, C.H., Steneck, R.S., Tegner,
M.J., and R.R. Warner, 2001. Historical Overfishing and the Recent Collapse of
Coastal Ecosystems. Science 293: 629-637.
Lenihan, H.S. 1999. Physical-Biological Coupling on Oyster Reefs: How Habitat
Structure Influences Individual Performance. Ecological Monographs 63(3):251-275.
Leonard, L.A. 1997. Controls of sediment transport and deposition in an incised
mainland marsh basin, southeastern North Carolina. Wetlands, 17(2):263-274.
Mallin, M.A., Paerl, H.W., Rudek, J., and P.W. Bates, 1993. Regulation of Estuarine
Primary Production by Watershed Rainfall and River Flow. Marine Ecology Progress
Series 93:199-203.
Mallin, M.A., Esham, E.C., Williams, K.E., and J.E. Nearhoof, 1999. Tidal Stage
Variability of Fecal Coliform and Chlorophyll a Concentrations in Tidal Creeks.
Marine Pollution Bulletin 38(5):414-422.
Mann, R., 2000. Restoring the Oyster Reef Communities in the Chesapeake Bay: A
Commentary. Journal of Shellfish Research 19(1):335-339.
Meyer, D.L. and E.C. Townsend. 2000. Faunal Utilization of Created Intertidal Eastern
Oyster (Crassostrea virginica) Reefs in the Southeastern United States. Estuaries
23(1):34-45.
Ulanowicz, R.E. & J.H. Tuttle. 1992. The Trophic Consequences of Oyster Stock
Rehabilitation in Chesapeake Bay. Estuaries 15(3): 298-306.
Welschmeyer, N.A., 1994. Fluorometric Analysis of Chlorophyll a in the Presence of
Chlorophyll b and phaeopigments. Limnology and Oceanography 39:1985-1992.
18.0 References Cited
APHA. 1995. Standard Methods for the Examination of Water and Wastewater, 19th
ed. American Public Health Association, Washington, D.C.
Hecky, R.E. and P. Kilham. 1988. Nutrient limitation of phytoplankton in freshwater and
marine environments: A review of recent evidence on the effects of enrichment.
Limnology and Oceanography 33:796-822.
Mallin, M.A., L.B. Cahoon, J.J. Manock, J.F. Merritt, M.H. Posey, R.K. Sizemore, W.D. Webster and T.D. Alphin. 1998a. A Four-Year Environmental Analysis of New
Hanover County Tidal Creeks, 1993-1997. CMSR Report No. 98-01, Center for
Marine Science Research, University of North Carolina at Wilmington, Wilmington,
N.C.
Mallin, M.A., L.B. Cahoon, J.J. Manock, J.F. Merritt, M.H. Posey, T.D. Alphin, D.C.
Parsons and T.L. Wheeler. 1998b. Environmental Quality of Wilmington and New
Hanover County Watersheds, 1997-1998. CMSR Report 98-03. Center for Marine Science Research, University of North Carolina at Wilmington, Wilmington, N.C.
Mallin, M.A., S.H. Ensign, D.C. Parsons and J.F. Merritt. 1999. Environmental Quality of
Wilmington and New Hanover County Watersheds, 1998-1999. CMSR Report No.
99-02. Center for Marine Science Research, University of North Carolina at
Wilmington, Wilmington, N.C.
Mallin, M.A. and T.L. Wheeler. 2000. Nutrient and fecal coliform discharge from coastal
North Carolina golf courses. Journal of Environmental Quality 29:979-986.
Mallin, M.A., S.H. Ensign, D.C. Parsons, V.L. Johnson and J.F. Merritt. 2000a.
Environmental Quality of Wilmington and New Hanover County Watersheds, 1999-
2000. CMSR Report No. 00-02. Center for Marine Science, University of North
Carolina at Wilmington, Wilmington, N.C.
Mallin, M.A., K.E. Williams, E.C. Esham and R.P. Lowe. 2000b. Effect of human
development on bacteriological water quality in coastal watersheds. Ecological
Applications 10:1047-1056.
Mallin, M.A., L.B. Cahoon, R.P. Lowe, J.F. Merritt, R.K. Sizemore and K.E. Williams.
2000c. Restoration of shellfishing waters in a tidal creek following limited dredging.
Journal of Coastal Research 16:40-47.
NCDEHNR. 1996. Water Quality Progress in North Carolina, 1994-1995 305(b) Report.
Report No. 96-03. North Carolina Department of Environment, Health, and Natural
Resources, Division of Water Quality. Raleigh, N.C.
Parsons, T.R., Y. Maita and C.M. Lalli. 1984. A Manual of Chemical and Biological Methods for Seawater Analysis. Pergamon Press, Oxford. 173 pp.
Schlotzhauer, S.D. and R.C. Littell. 1987. SAS system for elementary statistical
analysis. SAS Institute, Inc., SAS Campus Dr., Cary, N.C.
U.S. EPA. 1997. Methods for the Determination of Chemical Substances in Marine and
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Welschmeyer, N.A. 1994. Fluorometric analysis of chlorophyll a in the presence of
chlorophyll b and phaeopigments. Limnology and Oceanography 39:1985-1993.
19.0 Acknowledgments
Funding for this research was provided by New Hanover County, the City of
Wilmington, the North Carolina Clean Water Management Trust Fund and the
University of North Carolina at Wilmington. For project facilitation and helpful
information we thank Paul Foster, Dexter Hayes, Patrick Lowe, David Mayes, Chris O’Keefe, Rick Shiver and Dave Weaver. For field and laboratory assistance we
thank Abbey Chrystal, Jesse Cook, Heather CoVan, Scott Ensign, Jen Hardin, Matt
McIver, Amy Roberts, Laura Shepherd, David Wells and Tara Williams.
20.0 Appendix A. North Carolina Water Quality standards for selected parameters (NCDEHNR 1996).
_____________________________________________________________________
Parameter Standard
_____________________________________________________________________
Dissolved oxygen 5.0 ppm (mg/L)
Turbidity 25 NTU (tidal saltwater)
50 NTU (freshwater)
Fecal coliform counts 14 CFU/100 mL (shellfishing waters), and more than 10% of
the samples cannot exceed 43 CFU/100 mL.
200 CFU/100 mL (human contact waters)
Chlorophyll a 40 ppb (µg/L)
_____________________________________________________________________
CFU = colony-forming units
mg/L = milligrams per liter = parts per million
µg/L = micrograms per liter = parts per billion
21.0 Appendix B. Use support of Class C surface waters in Wilmington and New Hanover County watersheds based on August 2000 – July 2001 data (where available)
for chlorophyll a, dissolved oxygen, turbidity, and fecal coliform based on North Carolina
state standards**.
_____________________________________________________________________
FS (fully supporting) – state standard exceeded in < 10% of the measurements
PS (partially supporting) – state standard exceeded in 11-25% of the measurements NS (non supporting) – state standard exceeded in >25% of the measurements
_____________________________________________________________________
Watershed Station Chlor a DO Turbidity Fecal coliforms*
Barnard’s Creek BNC-TR FS FS FS NS
BNC-CB FS FS FS NS BNC-EF FS PS FS NS
BNC-AW FS PS FS NS
BNC-RR FS PS PS PS
Bradley Creek BC-CA FS PS FS NS BC-CR FS FS FS -
BC-SB PS FS FS -
BC-SBU FS FS FS -
BC-NB FS PS FS -
BC-NBU FS FS FS - BC-76 FS PS FS -
Burnt Mill Creek BMC-AP1 FS PS FS NS
BMC-AP2 FS FS FS NS
BMC-AP3 FS FS FS PS BMC-PP PS NS FS NS
Futch Creek FC-4 FS FS FS FS
FC-6 FS PS FS FS
FC-8 FS PS FS FS FC-13 FS NS FS FS
FC-17 FS NS FS FS
FOY FS NS FS FS
Greenfield Lake GL-SS1 FS NS FS NS GL-SS2 FS FS FS NS
GL-LC FS NS FS NS
GL-JRB FS NS FS NS
GL-LB FS NS FS NS
GL-2340 FS NS FS NS GL-YD FS FS FS NS
GL-P PS FS FS NS
Hewletts Creek PVGC-9 FS PS FS NS HC-M FS FS FS FS
HC-2 FS FS FS FS
HC-3 FS FS FS FS
HC-NWB FS PS FS NS
NB-GLR FS PS FS NS MB-PGR FS FS FS NS
SB-PGR FS PS FS NS
Howe Creek HW-FP FS FS FS -
HW-GC FS FS FS - HW-GP FS FS FS -
Motts Creek MOT-RR FS PS PS NS
Pages Creek PC-M FS FS FS FS PC-OL FS FS FS FS
PC-CON FS FS FS FS
PC-OP FS PS FS FS
PC-LD FS FS FS FS
PC-BDDS FS PS FS FS PC-WB FS PS FS FS
PC-BDUS FS NS PS FS
PC-H FS NS FS FS
Smith Creek SC-23 FS PS PS NS SC-CH FS PS PS PS
Upper and Lower UCF-PS FS FS FS NS
Cape Fear LCF-GO PS FS PS PS
Whiskey Creek WC-NB FS PS FS -
WC-SB FS FS FS -
WC-MLR FS PS PS -
WC-AB FS PS FS -
WC-MB FS PS FS - _____________________________________________________________________
* fecal coliform category used here is based on the human contact standard of 200
CFU/100 mL, not the shellfishing standard of 14 CFU/100 mL.
** NCDWQ only lists fecal coliform contaminated waters as NS if five samples are
collected in a 30-day period and standard is exceeded > 25% of the time; thus, this appendix should be considered a guide for polluted waters rather than a legal standard.
22.0 Appendix C. GPS coordinates for New Hanover County Tidal Creek stations and the Wilmington Watersheds Project sampling stations.
_____________________________________________________________________
Watershed Station GPS coordinates
Barnard’s Creek BNC-TR N 34 10.094 W 77 55.931
BNC-CB N 34 09.520 W 77 54.714 BNC-EF N 34 10.162 W 77 55.491
BNC-AW N 34 09.890 W 77 55.546
BNC-RR N 34 89.524 W 77 56.277
Bradley Creek BC-CA N 34 13.954 W 77 51.995 BC-CR N 34 13.846 W 77 51.141
BC-SB N 34 13.186 W 77 50.747
BC-SBU N 34 13.035 W 77 51.246
BC-NB N 34 13.290 W 77 50.643
BC-NBU N 34 13.959 W 77 51.141 BC-76 N 34 12.884 W 77 50.014
Burnt Mill Creek BMC-AP1 N 34 13.756 W 77 51.995
BMC-AP2 N 34 13.756 W 77 53.875
BMC-AP3 N 34 13.756 W 77 54.086 BMC-PP N 34 14.551 W 77 55.507
Futch Creek FC-4 N 34 18.089 W 77 44.797
FC-6 N 34 18.180 W 77 45.042
FC-8 N 34 18.252 W 77 45.234 FC-13 N 34 18.212 W 77 45.458
FC-17 N 34 18.220 W 77 45.825
FOY N 34 18.425 W 77 45.422
Greenfield Lake GL-SS1 N 34 11.978 W 77 55.468 GL-SS2 N 34 12.023 W 77 55.771
GL-LC N 34 12.451 W 77 55.788
GL-JRB N 34 12.756 W 77 55.884
GL-LB N 34 12.867 W 77 56.132
GL-2340 N 34 11.914 W 77 56.136 GL-YD N 34 12.421 W 77 55.872
GL-P N 34 12.822 W 77 56.617
Hewletts Creek PVGC-9 N 34 11.499 W 77 53.505
HC-M N 34 10.938 W 77 50.333
HC-2 N 34 11.234 W 77 50.584
HC-3 N 34 11.414 W 77 51.050
HC-NWB N 34 11.707 W 77 51.693 NB-GLR N 34 11.870 W 77 51.790
MB-PGR N 34 11.884 W 77 52.253
SB-PGR N 34 11.415 W 77 51.883
Howe Creek HW-M N 34 14.859 W 77 47.231 HW-FP N 34 15.266 W 77 47.693
HW-GC N 34 15.269 W 77 48.307
HW-GP N 34 15.327 W 77 48.918
HW-DT N 34 15.337 W 77 49.171
Motts Creek MOT-RR N 34 09.520 W 77 54.963
Pages Creek PC-M N 34 16.205 W 77 46.280
PC-OL N 34 16.470 W 77 46.540
PC-CON N 34 16.646 W 77 46.658 PC-OP N 34 16.975 W 77 46.819
PC-LD N 34 16.840 W 77 47.097
PC-BDDS N 34 16.886 W 77 47.650
PC-WB N 34 16.581 W 77 47.749
PC-BDUS N 34 16.639 W 77 48.092 PC-H N 34 16.505 W 77 47.888
Smith Creek SC-23 N 34 15.477 W 77 55.180
SC-CH N 34 15.538 W 77 56.323
Upper and Lower UCF-PS N 34 14.523 W 77 56.903
Cape Fear LCF-GO N 34 12.738 W 77 56.762
Whiskey Creek WC-NB N 34 10.082 W 77 52.589
WC-SB N 34 09.561 W 77 52.482 WC-MLR N 34 09.608 W 77 51.980
WC-AB N 34 09.580 W 77 51.706
WC-MB N 34 09.449 W 77 51.384
_____________________________________________________________________
23.0 Appendix D. University of North Carolina at Wilmington reports and papers concerning water quality in New Hanover County’s tidal creeks.
Reports
Merritt, J.F., L.B. Cahoon, J.J. Manock, M.H. Posey, R.K. Sizemore, J. Willey and W.D. Webster. 1993. Futch Creek Environmental Analysis Report. Center for Marine
Science Research, University of North Carolina at Wilmington, Wilmington, N.C.
Mallin, M.A., L.B. Cahoon, E.C. Esham, J.J. Manock, J.F. Merritt, M.H. Posey and R.K.
Sizemore. 1994. Water Quality in New Hanover County Tidal Creeks, 1993-1994.
Center for Marine Science Research, University of North Carolina at Wilmington, Wilmington, N.C. 62 pp.
Mallin, M.A., L.B. Cahoon, J.J. Manock, J.F. Merritt, M.H. Posey, T.D. Alphin and R.K.
Sizemore. 1995. Water Quality in New Hanover County Tidal Creeks, 1994-1995.
Center for Marine Science Research, University of North Carolina at Wilmington,
Wilmington, N.C. 67 pp.
Mallin. M.A., L.B. Cahoon, J.J. Manock, J.F. Merritt, M.H., Posey, R.K. Sizemore, T.D.
Alphin, K.E. Williams and E.D. Hubertz. 1996. Water Quality in New Hanover County
Tidal Creeks, 1995-1996. Center for Marine Science Research, University of North
Carolina at Wilmington, Wilmington, N.C. 67 pp.
Mallin, M.A., L.B. Cahoon, J.J. Manock, J.F. Merritt, M.H. Posey, R.K. Sizemore, W.D.
Webster and T.D. Alphin. 1998. A Four-Year Environmental Analysis of New
Hanover County Tidal Creeks, 1993-1997. CMSR Report No. 98-01, Center for
Marine Science Research, University of North Carolina at Wilmington, Wilmington,
N.C.
Mallin, M.A., L.B. Cahoon, J.J. Manock, J.F. Merritt, M.H. Posey, T.D. Alphin, D.C. Parsons and T.L. Wheeler. 1998. Environmental Quality of Wilmington and New
Hanover County Watersheds, 1997-1998. CMSR Report 98-03. Center for Marine
Science Research, University of North Carolina at Wilmington, Wilmington, N.C.
Mallin, M.A., S.H. Ensign, D.C. Parsons and J.F. Merritt. 1999. Environmental Quality of
Wilmington and New Hanover County Watersheds, 1998-1999. CMSR Report No.
99-02. Center for Marine Science Research, University of North Carolina at
Wilmington, Wilmington, N.C.
Mallin, M.A., L.B. Cahoon, S.H. Ensign, D.C. Parsons, V.L. Johnson and J.F. Merritt.
2000. Environmental Quality of Wilmington and New Hanover County Watersheds,
1999-2000. CMS Report No. 00-02. Center for Marine Science, University of North
Carolina at Wilmington, Wilmington, N.C.
Peer-Reviewed Journal Papers
Mallin, M.A., E.C. Esham, K.E. Williams and J.E. Nearhoof. 1999. Tidal stage variability
of fecal coliform and chlorophyll a concentrations in coastal creeks. Marine Pollution
Bulletin 38:414-422.
Mallin, M.A. and T.L. Wheeler. 2000. Nutrient and fecal coliform discharge from coastal
North Carolina golf courses. Journal of Environmental Quality 29:979-986.
Mallin, M.A., K.E. Williams, E.C. Esham and R.P. Lowe. 2000. Effect of human
development on bacteriological water quality in coastal watersheds. Ecological
Applications 10:1047-1056.
Mallin, M.A., L.B. Cahoon, R.P. Lowe, J.F. Merritt, R.K. Sizemore and K.E. Williams.
2000. Restoration of shellfishing waters in a tidal creek following limited dredging.
Journal of Coastal Research 16:40-47.
Mallin, M.A., J.M. Burkholder, L.B. Cahoon and M.H. Posey. 2000. The North and
South Carolina coasts. Marine Pollution Bulletin 41:56-75. Mallin, M.A., S.H. Ensign, M.R. McIver, G.C. Shank and P.K. Fowler. 2001. Demographic, landscape, and meteorological factors controlling the microbial pollution of coastal waters. Hydrobiologia 460:185-193.