2002-2003 Final Report
ENVIRONMENTAL QUALITY OF WILMINGTON AND
NEW HANOVER COUNTY WATERSHEDS
2002-2003
by
Michael A. Mallin, Lawrence B. Cahoon, Martin H. Posey, Virginia L. Johnson,
Troy D. Alphin, Douglas C. Parsons, and James F. Merritt
CMS Report 04-01
Center for Marine Science
University of North Carolina at Wilmington
Wilmington, N.C. 28409
January, 2004
www.uncw.edu/cmsr/aquaticecology/tidalcreeks
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 10 of the New Hanover County
Tidal Creeks Project and Year 6 of the Wilmington Watersheds Project. Water quality
data are presented from a watershed perspective, regardless of political boundaries. The combined programs involved 12 watersheds and 52 sampling stations. In this
summary we first present brief water quality overviews for each watershed from August
2002 – July 2003 (Tidal Creeks) or August 2002 – September 2003 (Wilmington
Watersheds), and then discuss key results of special studies conducted over the past
two years.
Barnards Creek – There was a fecal coliform bacterial pollution problem at all three of
the stations sampled in the Barnard’s Creek watershed, with the highest fecal coliform
counts at the station on Carolina Beach Rd. Lower Barnard’s Creek at River Road had
poor water quality as judged by turbidity and low dissolved oxygen, and there was increased loading of nitrogen at all three stations compared with the 2001-2002 study.
However, BOD at the River Road station decreased from the previous year.
Bradley Creek – Turbidity was not problematic during 2002-2003. Low dissolved
oxygen was an occasional problem in brackish waters of the creek during summer and fall. Elevated nitrogen and phosphorus levels enter the creek in both the north and
south branches, but major algal blooms were not seen during the sampling period.
Fecal coliform bacteria were only sampled at the station at College Acres, which proved
to be contaminated on 82% of the occasions sampled.
Burnt Mill Creek – A sampling station on Burnt Mill Creek at Princess Place had
substandard dissolved oxygen during 50% of the sampling trips. This station also had
very poor microbiological water quality, exceeding the standard for human contact in 11
of 12 samples, with a geometric mean of 1162 CFU/100 mL. The station just upstream
of Ann McCrary pond also had severe fecal coliform contamination, exceeding the standard on 92% of sample occasions. The effectiveness of Ann McCrary wet
detention pond on Randall Parkway as a pollution control device was not good last
year. There were no statistically significant reductions in any of the pollutant
parameters due to passage through the pond. 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 were not seen in 2002-2003. Dissolved oxygen and turbidity concentrations were minor
problems last year. 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 all three stations 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. However, excessive algal blooms were not recorded in the
lake in 2002-2003. 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 also prevalent at all in-lake and tributary stations
during 2002-2003, increasing over the previous year as a result of the breaking of the
drought and increased stormwater runoff.
A large regional wet detention pond on the tributary Silver Stream did a good job of reducing pollutant loads to the lake from this drainage. Statistically significant
reductions in orthophosphate, total phosphorus, and conductivity were all realized.
However, contrary to previous years, nitrogen and fecal coliform bacteria were not
significantly reduced, likely because of construction activities occurring along the lower
pond. 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.
Hewletts Creek – This creek received higher nitrate loading in its three upper branches
compared with last year, due to the end of the drought. One major algal bloom exceeding the State standard occurring in the north branch near Greenville Loop Road.
The middle branch had the highest nutrient concentrations, largely derived from two golf
courses. Low dissolved oxygen was not a problem in 2002-2003. Fecal coliforms were
not sampled in Hewletts Creek in 2002-2003, except at a station exiting the Pine Valley
Country Club golf course, where the State standard was exceeded 75% of occasions sampled.
Howe Creek – Five stations were sampled in Howe Creek in 2002-2003. The lower
creek maintained good water quality. A notable decrease in the number of algal
blooms has occurred in Howe Creek below Graham Pond since a wetland enhancement was performed in 1998. In the upper creek there were a few problems
with low dissolved oxygen and occasional algal blooms. Fecal coliform bacteria counts
were low near the ICW, moderate in mid-creek, and high in the uppermost station
during 2002-2003.
Motts Creek – This creek was sampled at only one station, at River Road. Low
dissolved oxygen was a problem on 42% of the sampling occasions in 2002-2003, and
turbidity and suspended sediments were a periodic problem. Fecal coliform pollution
was a frequent (58% of the time) problem at this station. Biochemical oxygen demand
(BOD5) and algal blooms decreased from the previous year.
Pages Creek – This creek maintained generally good water quality during 2002-2003.
Turbidity, nutrient loading and phytoplankton growth was low, even at the most
anthropogenically-impacted stations. However, there was periodic low dissolved
oxygen in warmer months at some stations draining Bayshore Drive. Pages Creek was not sampled for fecal coliform bacteria during 2002-2003. 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 an algal bloom exceeding 30 µg/L of chlorophyll a occurred once at the
23rd St. station. Low dissolved oxygen problems occurred 33% of the time and 41% of
the time at our two Smith Creek stations during 2002-2003. However, BOD levels
declined from the previous year.
Lower Cape Fear Watershed – Sampling was continued in the creek draining Greenfield Lake into the Cape Fear River. Fecal coliform concentrations exceeded the
state standard for human contact waters on 17% of the sampling occasions during
2002-2003. There was a fish kill here in September 2003 of about 450 individuals.
Whiskey Creek – Whiskey Creek had relatively high nutrient loading but generally low chlorophyll a concentrations in 2002-2003. There were several incidents of low
dissolved oxygen at two of the five stations sampled this year, but high turbidity was not
a problem. Fecal coliform bacteria counts were high in the upper north and south
stations and moderate in the mid-creek station in 2002-2003.
Water Quality Station 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 numerical standards to the water bodies described in
this report, based on 2002-2003 data, and have designated each station as good, fair,
and poor accordingly. Our analysis shows that (based on fecal coliform standards for human contact waters) two of the three Barnards Creek stations were rated poor quality. All three stations in Burnt Mill Creek were rated as poor in 2002-2003. Futch
Creek rated good for fecal coliform bacteria, including for shellfishing throughout the
lower creek. Greenfield Lake and its tributaries rated poor microbiological water quality
throughout. The one station in Hewletts Creek sampled for fecal coliforms last year was rated poor. The uppermost station in Howe Creek was rated poor, and the middle two were rated fair, respectively, while the lower two were rated good. Lower Motts
Creek was rated poor and both of the Smith Creek stations were rated poor. The
Lower Cape Fear station was rated fair for fecal coliforms. We also list ratings for
chlorophyll a, dissolved oxygen and turbidity in Appendix B, with Greenfield Lake, Smith
Creek and Motts Creek having generally poor ratings for dissolved oxygen.
Fecal coliform contamination of sediments - Sediments in the Bradley Creek watershed
were sampled for fecal coliform bacteria, and showed a variable but significant
population of fecal coliforms at all times and locations sampled. At all sites, suspension
of the sediments by physical forces would have sufficed to create water column concentrations of fecal coliforms high enough to mandate closure to shellfishing, and, in
several cases, to close these waters to human body contact. Direct body contact with
sediments, such as by wading or manual disturbance of the sediments, would likely be
particularly hazardous, assuming that sediment fecal coliform concentrations indicate
pathogen presence. When one adds in the fecal coliforms normally suspended in the
overlying water as well, then disturbance of the sediments can add a significant health threat to certain water bodies.
Sediment phosphate levels in these samples were not statistically related to fecal
coliform bacteria abundance in estuarine sediments. However, water temperature had
a significant effect on sediment coliform counts. Coliform counts were lowest at low temperatures and maximal at moderate temperatures, and low at high temperatures.
Fecal coliform contamination of tidal creeks in New Hanover County may be driven by a
complex relationship between storm water runoff, animal sources of fecal matter, and a
selection of environmental factors. A much larger study, funded by Sea Grant, is
scheduled to occur during 2004-2006.
Tidal Creek Oyster Reef Studies – The health and habitat values of oyster reefs in
several tidal creeks were studied. The results suggest considerable variability in oyster
reef characteristics among the New Hanover tidal creeks examined. In 2001 Pages
Creek was described as having “high shell coverage, relatively high densities of live oysters (compared to other creeks examined), and intermediate vertical relief”, while
Hewletts Creek was defined as intermediate among the four creeks overall with
“relatively high live oyster densities, but low relief”. As noted previously live oyster
densities in Pages and Hewletts Creeks were greater than measurements in Howe or
Whiskey Creeks during 2001 but declined in the 2003 measurements. This is a source of some concern because we also recorded an increase in the amount of shell hash
coverage compared to total oyster shell coverage (culms + shell hash). Our concern
here is that this change may reflect a decline in the oyster populations within these
areas. Data from an associated project looking at settlement within the Hewletts Creek
system (during late 2002 and early 2003) shows that larvae did recruit to that system, suggesting that factors other than larval supply may be primarily responsible for this
pattern. Measurements of reef complexity were moderate for both Pages and Hewletts
Creeks indicating the presence of some high relief culms. Although these same data
showed that the amount of open space within reefs at these two creeks was variable,
with some reefs having >50% of the area within the reef as open space. These data would seem to indicate that reefs in these two systems demonstrate a high degree of
variability among years and give some indication of the dynamic nature of oyster reef
formation. In many cases the most complex oyster habitats may be those that provide
both oyster structure and open patches within the reef proper. The question that we
must now focus on is at what point do oyster reefs provide the greatest benefits to other organisms (as habitat, refuge, and as system modifiers) while still providing the
aggregate needs for healthy oysters and good settlement structure for larvae to
maintain the reef integrity.
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
6.0 Greenfield Lake 15
7.0 Hewletts Creek 20
8.0 Howe Creek 24 9.0 Motts Creek 30
10.0 Pages Creek 33
11.0 Smith Creek 35
12.0 Lower Cape Fear 38
13.0 Whiskey Creek 40 14.0 Fecal Contamination of Tidal Creek Sediments 43
15.0 Tidal Creeks Oyster Reef Studies 51
16.0 Watersheds Report References Cited 63
17.0 Acknowledgments 65
18.0 Appendix A: Selected N.C. water quality standards 66 19.0 Appendix B: UNCW Watershed Station Ratings 67
20.0 Appendix C: GPS coordinates for the New Hanover County 69
21.0 Tidal Creek and Wilmington Watersheds sampling stations 70
21.0 Appendix D: UNCW reports and papers related to tidal creeks 72
(Cover by Heather Wells and Virginia Johnson)
1.0 Introduction
In 1993, scientists at the UNC Wilmington Center for Marine Science Research
began 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). In 1999-2000 Whiskey Creek was added to the matrix of tidal creeks analyzed.
Additionally, in October 1997 the Center for Marine Science 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 five years we have produced combined Tidal Creeks –
Wilmington City Watersheds reports (Mallin et al. 1998b; 1999; 2000a; 2002). In the
present report we present results of continuing studies from August 2002 - July 2003 in the tidal creek complex and August 2002 – September 2003 in 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), suspended solids, and BOD in selected creeks.
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 25 mm Millipore AP40 glass fiber filters (nominal pore size 1.0 micrometer) 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. 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 2002 through September 2003. 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, except filters were ground
using a teflon grinder prior to extraction.
For two wet detention ponds (Ann McCrary Pond on Burnt Mill Creek and Silver Stream Pond in the Greenfield Lake 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
single family and multifamily housing construction has occurred upstream of Carolina
Beach Rd. in the St. Andrews Dr. area; another major housing development is planned
for the area east of River Road and between Barnard’s and Mott’s Creeks. We 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), and this can no longer be considered a background site. Thus, sampling at
this site was stopped after December 2002. The BNC-CB site is near Carolina Beach
Road and drains an area hosting construction activities. BNC-TR exceeded the state
fecal coliform standard of 200 CFU/100 mL on 50% of the sampling trips and BNC-CB
exceeded the standard on 75% of the trips (Table 2.1; Appendix B). Both of these sites were thus significantly impaired by elevated fecal coliform counts during 2002-2003.
Total nitrogen (TN) showed an increase over 2001-2002, but chlorophyll a levels were
unremarkable at these sites, and turbidity was low.
We report here water quality data from the estuarine site on River Road. BNC-
RR had average salinity of 5.1 ppt with a range of 0.1-21.4 ppt. Lower Barnard’s Creek had dissolved oxygen levels below 5 mg/L on five occasions out of 11 samples in 2002-
2003, as compared with two out of twelve in 2001-2002. Concentrations of nutrient
species did not increase over the 2001-2002 values at this station, except for total
nitrogen. Turbidity on average was high (44 NTU), and exceeded the state standard for
estuarine waters of 25 NTU five times, same as the 2001-2002 year. Total suspended solids concentrations were generally high, particularly in August and September of
2002. BOD5 was sampled 11 times at BNC-RR last year, yielding a median of 1.5 and
a mean of 1.4 mg/L, which was down from the BOD5 concentrations found in the 2001-
2002 study (Mallin et al. 2003). Median and mean BOD20 in 2002-2003 was 5.9 and
6.0 mg/L, respectively, a decrease from the previous year. Fecal coliform counts exceeded the state standard two of 11 occasions for a 18% non-compliance rate, an
improvement over the previous year’s 33% non-compliance rate. Thus, this station can
be considered impaired by low dissolved oxygen, turbidity and fecal coliform loading.
Table 2.1. Mean and standard deviation of water quality parameters in Barnard’s Creek watershed, August 2002-September 2003. Fecal coliforms as geometric mean; N/P
ratio as median. BNC-TR was only sampled four times.
_____________________________________________________________________
Parameter BNC-TR BNC-CB BNC-RR
_____________________________________________________________________
DO (mg/L) 4.8 (1.7) 6.9 (1.5) 6.5 (2.7)
Turbidity (NTU) 90 (172) 12 (12) 44 (55)
TSS (mg/L) 13.8 (14.8) 5.4 (3.9) 38.5 (53.7)
Nitrate (mg/L) 0.060 (0.080) 0.069 (0.051) 0.215 (0.196) Ammon. (mg/L) 0.109 (0.051) 0.092 (0.058) 0.123 (0.059)
TN (mg/L) 1.317 (0.284) 0.894 (0.352) 1.417 (0.398)
Phosphate (mg/L) 0.050 (0.051) 0.034 (0.073) 0.067 (0.041)
TP (mg/L) 0.081 (0.056) 0.087 (0.103) 0.126 (0.040)
N/P molar ratio 22.1 33.4 12.6
Chlor. a (µg/L) 0.8 (0.1) 2.9 (3.1) 4.9 (3.9)
Fec. col.(/100 mL) 307 505 96
_____________________________________________________________________
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 2002-2003 (Table 3.1). The
standard of 25 NTU was not exceeded during our brackish water sampling except with
a construction-related episode in July 2003 (198 NTU - Table 3.1). There were only minor problems with low dissolved oxygen (hypoxia), with BC-NB having DO of less
than 5.0 mg/L on two occasions and BC-CA having substandard dissolved oxygen
conditions on three of 12 sampling occasions (Appendix B).
Table 3.1 Parameter concentrations at Bradley Creek sampling stations, August 2002-July 2003 (BC-CA from August 2003 – September 2003). Data as mean (SD) / range,
fecal coliform bacteria as geometric mean / range.
_____________________________________________________________________
Station Salinity Turbidity Dissolved Oxygen Fecal coliforms
(ppt) (NTU) (mg/L) (CFU/100 mL) _____________________________________________________________________
BC-76 28.8 (7.0) 9 (15) 7.7 (2.2) NA
9.0-34.2 2-55 5.0-11.0
BC-SB 12.5 (12.8) 25 (55) 7.4 (1.9) NA
0.1-31.6 2-198 4.9-11.1
BC-SBU 0.1 (0.0) 6 (6) 7.2 (1.4) NA
0.1-0.1 2-22 5.3-9.4
BC-NB 21.1 (11.6) 10 (9) 7.1 (2.2) NA
0.2-32.8 2-35 3.9-10.2
BC-NBU 0.1 (0.0) 9 (10) 7.6 (1.1) NA 0.1-0.2 3-40 6.1-9.3
BC-CR 0.1 (0.0) 4 (6) 7.6 (0.8) NA
0.0-0.1 0-18 6.5-8.8
BC-CA 0.1 (0.0) 8 (4) 6.3 (2.1) 1093
0.1-0.2 3-13 4.4-10.6 155-13000
_____________________________________________________________________
Only BC-CA was sampled for fecal coliform concentrations last year, with elevated counts exceeding the State standard of 200 CFU/100 mL occurring during 9 of
11 collections for an 82% exceedence rate (Table 3.1). We consider that station to have poor water quality in terms of fecal coliform counts (Appendix B).
Nitrate concentrations were highest at stations BC-CR, BC-SBU (upper south
branch) and BC-NBU. Nitrate increased considerably over the previous year (in some
cases more than doubling), possibly as a result of the drought breaking and increased streamflow (and stormwater runoff). Ammonium was also elevated at BC-CA, and low
at other locations. The highest orthophosphate levels were found at BC-CA, with
relatively low orthophosphate levels at the rest of the stations (Table 3.2). Bradley
Creek did not host excessive algal blooms in 2002-2003, except for a few minor blooms
at BC-CA (20-32 µg/L, Table 3.2).
Table 3.2. Nutrient and chlorophyll a data at Bradley Creek sampling stations, August
2002-July 2003 (BC-CA from August 2003 – September 2003). Data as mean (SD) /
range, nutrients in mg/L, chlorophyll a as µg/L.
_____________________________________________________________________ Station Nitrate Ammonium Orthophosphate Chlorophyll a
_____________________________________________________________________
BC-76 0.021 (0.032) 0.026 (0.024) 0.007 (0.007) 1.97 (1.6)
0.006-0.121 0.006-0.087 0.001-0.027 0.7-6.4
BC-SB 0.088 (0.058) 0.036 (0.023) 0.011 (0.013) 3.2 (2.3)
0.013-0.212 0.004-0.069 0.002-0.052 0.8-8.4
BC-SBU 0.186 (0.108) NA 0.009 (0.011) 2.5 (2.9) 0.044-0.464 0.001-0.044 0.2-10.2
BC-NB 0.029 (0.033) 0.032 (0.031) 0.009 (0.010) 3.9 (5.4)
0.005-0.123 0.006-0.105 0.001-0.036 0.7-20.5
BC-NBU 0.116 (0.047) NA 0.004 (0.007) 1.5 (2.7)
0.069-0.250 0.001-0.023 0.1-9.2
BC-CR 0.270 (0.060) NA 0.005 (0.007) 1.8 (2.9)
0.150-0.372 0.001-0.027 0.2-9.0
BC-CA 0.090 (0.056) 0.125 (0.073) 0.021 (0.012) 10.6 (9.6)
0.016-0.170 0.020-0.270 0.0102-0.045 1.7-32.0
_____________________________________________________________________
4.0 Burnt Mill Creek
The Burnt Mill Creek watershed was sampled just upstream of Ann McCrary
Pond on Randall Parkway (AP1), 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. The ability of this detention pond to reduce suspended sediments and fecal coliform bacteria, and its failure to reduce nutrient concentrations, was detailed in a scientific
journal article (Mallin et al. 2002b).
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. Ten out of 11 samples at AP1 had counts exceeding 200
CFU/100 mL. There was an October 2002 algal bloom at AP1 with a chlorophyll a
concentration of 54 µg/L and an August 2002 bloom at AP3 of 65 µg/L. No blooms exceeded the State standard for chlorophyll a at Princess Place.
The efficacy of the pond as a pollutant removal device was not good last year.
Average fecal coliforms were reduced during passage through the pond, but this
difference was not statistically significant (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. None of the nitrogen or phosphorus species were
significantly reduced during passage through the pond this year (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 former AP2 site (Fig.
4.1). 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 no 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, probably due to utilization of CO2 during photosynthesis in the pond.
As in previous studies, the Princess Place location experienced several water
quality problems during the sample period (Appendix B). Dissolved oxygen was
substandard on six of 11 sampling trips, for a non-compliance rate of 55%. The most
important issue, from a public health perspective, was the excessive fecal coliform counts, which maintained a geometric mean (1162 CFU/100 mL) far 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 9 of 11 samples, or 82% of the time. It is notable
that fecal coliform, suspended solids, 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).
Table 4.1. Mean and (standard deviation) of water quality parameters in Burnt Mill
Creek, August 2002 - September 2003. Fecal coliforms as geometric mean; N/P as
median. _____________________________________________________________________
Parameter BMC-AP1 BMC-AP3 BMC-PP
_____________________________________________________________________
DO (mg/L) 6.6 (1.7) 9.1 (1.8)** 5.7 (2.3)
Cond. (µS/cm) 226 (54) 219 (38) 303 (55)
pH 6.7 (0.3) 7.3 (0.6)** 7.1 (0.3)
Turbidity (NTU) 9 (6) 9 (8) 7 (4)
TSS (mg/L) 8.9 (7.1) 6.4 (3.2) 7.3 (2.8)
Nitrate (mg/L) 0.104 (0.091) 0.061 (0.046) 0.113 (0.088) Ammonium (mg/L) 0.094 (0.050) 0.081 (0.042) 0.121 (0.157)
TN (mg/L) 0.875 (0.154) 0.945 (0.307) 0.869 (0.214)
Phosphate (mg/L) 0.013 (0.010) 0.026 (0.041) 0.042 (0.058)
TP (mg/L) 0.082 (0.104) 0.069 (0.066) 0.089 (0.080)
N/P molar ratio 48.4 17.7 21.0 Fec. col. (/100 mL) 1162 285 914
Chlor. a (µg/L) 12.2 (14.8) 16.3 (18.5) 7.5 (9.4)
_____________________________________________________________________
* 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). During 2002-2003, there were
only two incidences of creek stations having turbidity levels exceeding the state
standard of 25 NTU. Low dissolved oxygen, was a problem only at FC-17 on two
occasions in 2002-2003 (Appendix B).
Table 5.1. Physical parameters at Futch Creek sampling stations, August 2002 - July
2003. Data given as mean (SD) / range.
_____________________________________________________________________
Station Salinity (ppt) Turbidity (NTU) Dissolved oxygen (mg/L)
_____________________________________________________________________
FC-4 33.4 (1.8) 6 (4) 8.1 (2.1)
29.3-36.2 1-14 5.4-11.7
FC-6 32.7 (2.0) 7 (4) 8.0 (2.1) 28.5-36.2 1-14 5.0-11.8
FC-8 32.0 (2.4) 7 (4) 7.7 (2.1)
27.5-36.3 2-14 4.5-11.4
FC-13 29.0 (3.3) 10 (7) 7.6 (2.5)
23.6-35.1 2-21 4.4-12.7
FC-17 24.1 (6.3) 11 (8) 6.9 (2.2)
9.7-35.5 3-31 3.9-10.5
FOY 28.9 (3.6) 10 (10) 7.7 (2.2)
23.8-35.8 2-38 4.3-11.9
_____________________________________________________________________
Nutrient concentrations in Futch Creek remained 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; Roberts
2002). The creek was free from algal blooms during our sampling visits (Table 5.2), even in the upper stations.
Table 5.2. Nutrient and chlorophyll a data at Futch Creek sampling stations, August
2002-July 2003. Data as mean (SD) / range, nutrients in mg/L, chlorophyll a as µg/L.
_____________________________________________________________________
Station Nitrate Ammonium Orthophosphate Chlorophyll a
_____________________________________________________________________
FC-4 0.007 (0.005) 0.022 (0.024) 0.005 (0.003) 1.2 (1.0) 0.001-0.017 0.001-0.091 0.001-0.010 0.5-3.8
FC-6 0.010 (0.008) NA 0.005 (0.004) 1.4 (1.1)
0.001-0.025 0.001-0.011 0.5-4.3
FC-8 0.015 (0.012) NA 0.005 (0.004) 1.7 (1.2)
0.003-0.041 0.001-0.012 0.5-4.4
FC-13 0.034 (0.032) NA 0.006 (0.005) 2.2 (2.0)
0.004-0.099 0.001-0.014 0.5-6.5
FC-17 0.051 (0.051) 0.037 (0.048) 0.009 (0.005) 3.7 (3.1)
0.003-0.163 0.001-0.177 0.001-0.018 0.7-10.4
FOY 0.039 (0.039) 0.029 (0.036) 0.006 (0.004) 2.5 (2.3) 0.003-0.116 0.006-0.141 0.001-0.013 0.5-7.1
_____________________________________________________________________
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 2002-2003 the lower creek through FC-8 maintained excellent microbiological water
quality for shellfishing (Table 5.3), and the mid-creek areas had good microbiological
water quality as well. 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, August 2002 - July 2003.
_____________________________________________________________________ Station FC-4 FC-6 FC-8 FC-13 FC-17 FOY
Geomean (CFU/100 mL) 1 1 0 2 17 5
% > 43 /100ml 0 0 0 0 17 17 _____________________________________________________________________
6.0 Greenfield Lake
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 were alligatorweed Alternanthera philoxeroides, pennywort
Hydrocotyle umbellate, water primrose Ludwigia leptocarpa and cattail Typha latifolia.
This pond’s performance as a nutrient removal system was mixed last year (Table 6.1). Statistically significant removal of orthophosphate (82%) and TP (71%) was achieved,
while reduction of ammonium was not statistically significant (10%), nor was reduction
of TN (28%). Average reduction of nitrate was high (85%), but the large variability
among concentrations led this to be statistically non-significant (although not
biologically non-significant). Turbidity and TSS were generally low at both locations this past year (Table 6.1). Fecal coliform concentrations at SS2 were not overly high, and
there was no significant reduction through the pond. The lack of significant nitrogen
removal may have resulted from construction activities near the lower end of the pond.
Dissolved oxygen significantly increased, because of aeration while passing through the
outfall and increased oxygenation through pond photosynthesis.
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 2002 – September 2003. As mean (standard deviation); geometric mean for
fecal coliform bacteria. _____________________________________________________________________
Parameter SS1 SS2
_____________________________________________________________________
DO (mg/L) 4.8 (1.5) 7.3 (2.1)**
Cond. (µS/cm) 331 (121) 163 (45)**
pH 6.8 (0.2) 7.0 (0.2)*
Turbidity (NTU) 3 (6) 6 (5) TSS (mg/L) 7.1 (12.1) 6.1 (6.1) Nitrate (mg/L) 0.450 (0.690) 0.069 (0.050)
Ammonium (mg/L) 0.232 (0.131) 0.209 (0.169)
TN (mg/L) 1.472 (0.733) 1.073 (0.397)
Phosphate (mg/L) 0.110 (0.117) 0.020 (0.014)* TP (mg/L) 0.223 (0.154) 0.064 (0.045)**
Chlorophyll a (µg/L) 1.5 (1.5) 17.0 (27.5)
Fecal col. (CFU/100 mL) 285 124
_____________________________________________________________________
* 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). All three tributaries suffered from extreme
hypoxia, with GL-JRB (Jumping Run Branch), GL-LB (creek at Lake Branch Drive) and
GL-LC (creek beside Lakeshore Commons) all showing average concentrations below
the state standard (DO < 5.0 mg/L). Dissolved oxygen levels were substandard eight of
11 times at GL-JRB, 10 of 11 times at GL-LC, and 10 of 11 times at GL-LB (Appendix B). Turbidity and suspended solids were generally low in the tributary stations (Table
6.2). Nitrate concentrations were highest at GL-LC, somewhat lower at GL-LB, and
lowest at GL-JRB (Table 6.2). Ammonium concentrations were highest at GL-LB, and
generally similar across the other two tributary stations. Orthophosphate
concentrations were highest at GL-LC, and similar at GL-LB and GL-JRB, and showed a general decrease from the previous year. 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) eight of 11 times at GL-LB, 9 of 11 times at GL-LC, and seven of 11 times at GL-JRB. This represents a worsening over 2001-2002, possibly resulting from the breaking
of the drought conditions that had subsequently reduced non-point source pollution.
Chlorophyll a levels were generally non-problematic in these streams (Table 6.2).
Table 6.2. Mean and (standard deviation) of water quality parameters in tributary
stations of Greenfield Lake, August 2002 - September 2003. Fecal coliforms as geometric mean; N/P ratio as median.
_____________________________________________________________________
Parameter GL-JRB GL-LB GL-LC
_____________________________________________________________________
DO (mg/L) 3.8 (2.4) 2.4 (2.0) 2.7 (1.7) Turbidity (NTU) 6 (5) 5 (2) 4 (4)
TSS (mg/L) 4.4 (3.1) 3.7 (1.3) 13.6 (22.7)
Nitrate (mg/L) 0.110 (0.095) 0.179 (0.215) 0.341 (0.321)
Ammonium (mg/L) 0.155 (0.099) 0.222 (0.123) 0.163 (0.090)
TN (mg/L) 1.076 (0.439) 1.204 (0.725) 1.337 (0.685) Phosphate (mg/L) 0.027 (0.016) 0.029 (0.019) 0.066 (0.054)
TP (mg/L) 0.060 (0.019) 0.084 (0.081) 0.127 (0.080)
N/P molar ratio 17.0 35.4 15.8
Fec. col. (/100 mL) 357 287 835
Chlor. a (µg/L) 7.4 (5.4) 4.0 (6.8) 5.9 (7.9)
_____________________________________________________________________
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). Low dissolved oxygen
affected GL-2340, GL-YD, and GL-P, with 45%, 50%, and 45% of the samples below
the state standard, respectively (Appendix B). Turbidity and suspended solids were low
to moderate at the three sites. Fecal coliform concentrations were problematic at all three stations. At GL-2340 the state standard was exceeded on four of 11 occasions,
at GL-YD it was exceeded on five of 10 occasions, and at GL-P it was exceeded on seven of 11 occasions in 2002-2003.
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 total phosphorus were highest at GL-YD (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 at GL-YD and GL-P should be primarily nitrogen-limited. Our
previous bioassay work indicated that this was indeed the case (Mallin et al. 1999).
However, N/P ratios were high at GL-2340 in 2002-2003, possibly a result of less
phosphorus inputs; thus, phytoplankton growth at GL-2340 should have been mainly P-
limited last year.
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.
However, algal blooms exceeding the state standard of 40 µg/L were not recorded in
our sampling during 2002-2003. Thus, during 2002-2003 Greenfield Lake proper was
impaired by high fecal coliform counts and low dissolved oxygen concentrations; its
tributary stations were also impaired by high fecal coliform counts and low dissolved
oxygen. The lake in general and its tributaries had lower P inputs and less algal blooms as compared with 2001-2002, but worse dissolved oxygen concentrations. Fecal
coliforms problems increased somewhat compared with the previous year.
Table 6.3. Mean and (standard deviation) of water quality parameters in Greenfield Lake sampling stations, August 2002 - September 2003. Fecal coliforms given as
geometric mean, N/P ratio as median.
_____________________________________________________________________
Parameter GL-2340 GL-YD GL-P
_____________________________________________________________________ DO (mg/L) 5.0 (1.6) 5.6 (3.5) 6.1 (4.4)
Turbidity (NTU) 2 (1) 4 (4) 3 (3)
TSS (mg/L) 4.0 (3.4) 14.2 (21.7) 4.9 (5.0)
Nitrate (mg/L) 0.098 (0.086) 0.054 (0.054) 0.041 (0.024)
Ammonium (mg/L) 0.119 (0.093) 0.271 (0.498) 0.087 (0.062) TN (mg/L) 0.926 (0.278) 2.086 (2.730) 1.268 (0.723)
Phosphate (mg/L) 0.013 (0.008) 0.028 (0.023) 0.033 (0.038)
TP (mg/L) 0.065 (0.081) 0.118 (0.139) 0.085 (0.070)
N/P molar ratio 29.5 14.4 10.7
Fec. col. (/100 mL) 147 182 429
Chlor. a (µg/L) 7.2 (10.1) 15.1 (8.5) 11.6 (6.8)
____________________________________________________________________
7.0 Hewletts Creek
Hewletts Creek was sampled at five tidally-influenced areas (HC-2, HC-3, 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 except for two occasions at NB-GLR and one occasion at SB-PGR (Tables 7.1 and 7.2). There were no incidents of hypoxia seen in our 2002-2003
sampling. Nitrate concentrations were somewhat 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). Nitrate concentrations in general were higher than 2001-
2002, likely a result of the breaking of the drought, leading to increased non-point source runoff pollution. This was also reflected by the elevated median N/P molar
ratios seen at the tidally influenced stations. The chlorophyll a data (Table 7.1) showed
that Hewletts Creek hosted a major algal bloom at NB-GLR (166 µg/L), and several
minor blooms at SB-PGR (34.9, 39.9, and 24.9 µg/L, respectively in April, June and July 2003. Algal blooms have been common in upper Hewletts Creek in the past (Mallin et
al. 1998a; 1999; 2002a). Fecal coliform bacterial counts were not performed for the
tidally influenced stations in 2002-2003.
Phosphate and nitrate were elevated leaving the golf course at PVGC-9 relative to the other stations (Tables 7.1 and 7.2). Nitrate leaving the course increased over the
previous year (2001-2002) study (Mallin et al. 2003a). Fecal coliform bacteria counts
exceeded State standards 75% of the time in 2002-2003 at PVGC-9, an increase over
last year. 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 (8,050 CFU/100 mL) occurred
in July 2003. 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 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 2002-July 2003.
_____________________________________________________________________
Parameter HC-2 HC-3
_____________________________________________________________________
Salinity 32.6 (2.5) 30.4 (3.7)
(ppt) 29.2-36.3 25.2-36.1
Turbidity 4 (3) 6 (3)
(NTU) 1-10 2-11
DO 7.8 (1.6) 7.6 (1.7)
(mg/L) 5.3-10.4 4.9-10.8
Nitrate 0.008 (0.008) 0.013 (0.013) (mg/L) 0.003-0.030 0.003-0.051
Ammonium 0.019 (0.019) NA
(mg/L) 0.003-0.075
Phosphate 0.004 (0.004) 0.005 (0.004)
(mg/L) 0.001-0.013 0.001-0.014
Mean N/P 20 NA
Median 16
Chlor a 1.3 (0.5) 1.7 (1.0)
(ug/L) 0.8-2.5 0.9-3.9
_____________________________________________________________________
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 2002-July 2003.
_____________________________________________________________________
Parameter NB-GLR SB-PGR MB-PGR PVGC-9
_____________________________________________________________________
Salinity 8.0 (9.6) 17.2 (9.4) 0.4 (0.7) 0.1 (0.0)
(ppt) 1.3-31.4 6.5-32.1 0.1-2.3 0.1-0.2
Turbidity 13 (8) 15 (8) 7 (9) 4 (3) (NTU) 5-27 3-26 1-31 1-10
DO 8.0 (1.7) 7.4 (2.0) 7.8 (1.4) 6.5 (1.5)
(mg/L) 5.1-10.5 4.0-11.4 6.0-10.1 5.0-9.3
Nitrate 0.119 (0.059) 0.049 (0.036) 0.235 (0.068) 0.417 (0.532)
(mg/L) 0.004-0.210 0.005-0.110 0.131-0.366 0.020-1.670
Ammonium 0.046 (0.021) 0.052 (0.061) 0.030 (0.015) 0.181 (0.153)
(mg/L) 0.022-0.094 0.006-0.238 0.009-0.060 0.010-0.401
Phosphate 0.018 (0.010) 0.008 (0.004) 0.014 (0.008) 0.016 (0.019)
(mg/L) 0.006-0.043 0.004-0.017 0.002-0.028 0.005-0.070
Mean N/P ratio 24 31 74 105 Median 21 25 42 93
Chlor a 19.0 (46.6) 11.5 (14.0) 3.1 (5.7) 2.5 (3.7)
(ug/L) 1.0-165.7 0.9-39.9 0.3-20.7 0.5-13.2
Fecal coliforms NA NA NA 537 CFU/100 mL 122-8050
_____________________________________________________________________
8.0 Howe Creek Water Quality
Howe Creek was sampled for physical parameters, nutrients, chlorophyll a , and
fecal coliform bacteria at five locations during 2002-2003 (HW-M, HW-FP, HW-GC,
HW-GP and HW-DT, Fig. 8.1). Turbidity was low near the ICW and exceeded North
Carolina water quality standards on only one occasion at HW-DT (Table 8.1; Appendix
B). Dissolved oxygen concentrations were generally good in Howe Creek, with HW-GC and HW-GP below the standard of 5.0 mg/L on two occasions each (Appendix B).
Nutrient levels were generally low in 2002-2003 (Table 8.2). Nitrate levels were
similar to 2001-2002 (Mallin et al. 2003a). Median inorganic molar N/P ratios were
moderate, indicating that nutrients were relatively balanced at all stations. There were
algal blooms of 50 µg/L as chlorophyll a at HW-DT and 60 µg/L at HW-DT. During the
early and mid-1990s there were frequent algal blooms occurring in Howe Creek at
station HW-GP, located just below Graham Pond. In the late 1990s a wetland
enhancement was performed in the upper portion of Graham Pond that involved
increasing the retention time of water before it could flow downstream and into Howe
Creek. By increasing retention time, more nutrients would be taken up by the wetland
plants and more denitrification would take place, reducing nutrient loading to the creek.
The results have been positive for Howe Creek (Fig. 8.2). The severity of algal blooms has considerably decreased at HW-GP since 1998, demonstrating that wetland
enhancement is a viable, and long-lasting means of reducing eutrophication in tidal
creeks. We recommend that further wetland acquisition and enhancement be
undertaken in the upper Howe Creek watershed to reduce impacts to the creek from
the ongoing construction along Military Cutoff.
Fecal coliform bacteria abundances were low near the Intracoastal Waterway,
moderate in mid-creek, and high in the uppermost stations (Table 8.1). HW-GC and
HW-GP exceeded the North Carolina human contact standard on two of eleven
occasions, and HW-DT exceeded the standard on four of eleven occasions (Appendix B). Over the period 1993 – 2003 fecal coliform abundances have remained similar at
the three lower creek stations (Fig. 8.3). However, a decrease was noted at the upper
two sites between 1993-2000 and 2001-2003. During the early period a considerable
amount of construction activity was ongoing close to the creek, first at Landfall and later
on the north side of the creek. After 2000 the near-creek construction activity slowed down greatly, allowing for revegetation and earth stabilization; this potentially accounted
for the fecal coliform decrease at HW-GP and HW-DT. Additionally, a severe drought
occurred during the latter period (particularly during 2002) that reduced rainfall-driven
runoff of pollutants into the tidal creeks, which would also help account for a fecal
bacteria decrease. At this writing a large amount of construction is occurring at the Mayfaire location along Military Cutoff. A student study in spring 2003 demonstrated
that runoff mitigative measures at Mayfaire during the earth-moving phase were doing a
good job of keeping fecal coliform bacteria from running off-site toward Howe Creek.
We will continue to monitor this area during subsequent construction and residential
development to assess any potential off-site pollutant runoff.
During early 2002 a new channel was dredged and Mason Inlet was
subsequently moved from its previous location at the north end of Wrightsville Beach to
a location 2500 ft north. There had been speculation that such an activity along the barrier islands would improve tidal exchange in the tidal creeks and reduce fecal
coliform counts. Creek mouth dredging during 1995 and 1996 in Futch Creek had that
effect, increasing salinities and reducing fecal coliform counts significantly. Thus, we
compared six calendar months of Howe Creek salinity and fecal coliform data collected
before and after inlet moving to see if such a change did occur.
Sampling in nearby Howe Creek, directly across the Atlantic Intracoastal
Waterway from Mason Creek, showed little change either way in fecal coliform
abundance at the lower and middle creek stations before or after dredging. There was
a 43% decrease in fecal coliform concentrations at the uppermost Howe Creek station following inlet relocation. However, salinities collected at the same time as fecal
coliforms actually showed lower values (rather than higher) in Howe Creek following the
dredging of Mason Inlet. Additionally, statistical analysis showed a positive correlation
between rainfall and fecal coliform counts in upper Howe Creek. Thus, the fecal
coliform decrease in upper Howe Creek following inlet relocation appeared to be related to localized rainfall and runoff patterns rather than increased salinity resulting from inlet
relocation. The full report on the Mason Inlet monitoring project (Mallin et al. 2003b) is
available on-line at http://www.uncwil.edu/cmsr/aquaticecology/TidalCreeks/Index.htm.
UNCW graduate student Jason Hales carried out a number of tidal exchange studies in the creeks during 1998-2000. Results from Howe Creek showed an average
daily tidal exchange rate of 46% in July 1998 (Hales 2001). Repeating that study in
Howe Creek in August 2003 (after inlet moving) showed a decrease in average daily
tidal exchange rate to 38% (Hales 2003). Thus, the dredging and moving of Mason
Inlet did not improve the circulation of Howe Creek. Hales (2003) did find an increase in tidal exchange rates from 2000 to 2003 in more distant Pages Creek, however.
Table 8.1. Water quality summary statistics for Howe Creek, August 2002-July 2003, as mean (st. dev.) / range.
Salinity Diss. oxygen Turbidity Chlor a Fecal coliforms
(ppt) (mg/L) (NTU) (µg/L) CFU/100 mL
_____________________________________________________________________
HW-M 33.1 (1.9) 7.6 (2.1) 6 (3) 1.6 (1.1) 3
28.2-34.9 4.7-10.8 3-12 0.5-3.2 1-143
HW-FP 33.1 (1.8) 7.5 (2.2) 5 (2) 1.3 (0.9) 1
28.7-34.9 4.7-10.8 2-10 0.4-3.1 0-181
HW-GC 29.7 (4.3) 7.2 (2.3) 8 (3) 2.4 (2.3) 23
20.3-34.4 4.3-11.0 3-14 0.4-7.4 0-870
HW-GP 19.2 (9.4) 6.9 (2.1) 8 (4) 6.0 (6.2) 93 2.5-32.1 4.5-11.1 3-15 0.9-18.0 17-1455
HW-DT 4.2 (5.6) 7.9 (2.1) 13 (9) 20.3 (21.1) 201
0.1-15.2 4.9-11.5 5-38 1.1-60.2 21-2020
Table 8.2. Nutrient concentration summary statistics for Howe Creek, August 2002-July
2003, 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-M 0.007 (0.005) 0.022 (0.013) 0.004 (0.003) 24
0.001-0.018 0.004-0.049 0.001-0.009 16
HW-FP 0.006 (0.007) 0.021 (0.012) 0.005 (0.003) 16
0.001-0.028 0.006-0.039 0.001-0.010 16
HW-GC 0.008 (0.006) NA 0.006 (0.004) NA
0.002-0.023 0.001-0.012
HW-GP 0.012 (0.009) 0.023(0.013) 0006 (0.004) 26
0.001-0.029 0.008-0.041 0.001-0.011 14
HW-DT 0.027 (0.029) 0.029(0.031) 0.008 (0.006) 24 0.001-0.078 0.007-0.117 0.001-0.020 17
____________________________________________________________________
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 residential development is scheduled
for construction upstream of the sampling site and between Mott’s and Barnard’s
Creeks. Recently, extensive commercial development has occurred along Carolina
Beach Road near its junction with Highway 421.
Dissolved oxygen concentrations were below 5.0 mg/L on 45% of the occasions
sampled, a lower compliance rate than during the 2001-2002 sampling (Mallin et al.
2003). Turbidity was occasionally a problem, exceeding the state brackish water
standard of 25 NTU on three of 11 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 530 CFU/100 mL well exceeding
the state standard of 200 CFU/100 mL, and monthly samples exceeding this standard
on seven of 11 occasions (Appendix B). Fecal coliform contamination worsened from
the previous year. Total nitrogen levels increased over the previous year’s study, but chlorophyll a concentrations remained below standard at all times, an improvement
over the previous year (Table 9.1). BOD5 was sampled on 11 occasions in 2002-2003,
yielding a mean value of 1.9 mg/L and a median value of 1.9 mg/L, which was lower
than the previous year (Mallin et al. 2003). Thus, this creek showed mixed water
quality, with algal blooms and BOD decreasing but dissolved oxygen and fecal coliform counts getting worse. Cessation of the commercial development activities near the
headwaters upstream may have contributed to the decrease in BOD and algal blooms
in the creek at River Road.
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 2002-September 2003. Fecal coliforms as geometric mean / range.
_____________________________________________________________________
Parameter MOT-RR
_____________________________________________________________________
Salinity (ppt) 2.5 (6.3)
0.1-21.3
TSS (mg/L) 26.3 (27.0) 7.8-97.0
Turbidity (NTU) 37 (34)
6-123
DO (mg/L) 5.5 (1.9)
3.4-9.7
Nitrate (mg/L) 0.092 (0.069)
0.015-0.220
Ammonium (mg/L) 0.091 (0.057)
0.005-0.210
Total nitrogen (mg/L) 1.188 (0.432) 0.838-2.133
Phosphate (mg/L) 0.037 (0.040)
0.005-0.135
Total phosphorus (mg/L) 0.490 (1.360)
0.020-4.590
Mean N/P ratio 18.7
Median 15.9
Chlor a (µg/L) 6.6 (4.9)
1.2-17.0
Fecal coliforms (CFU/100 mL) 530 24-6000
_____________________________________________________________________
10.0 Pages Creek
Pages Creek was sampled at three stations, two of which receive drainage from
developed areas (PC-BDUS and PC-BDDS - Fig. 10.1). During the past sample year
turbidity was low with no incidents of turbidity exceeding the state standard of 25 NTU
(Table 10.1). However, there were a few incidents of hypoxia during summers of 2002 and 2003, two each at the stations draining Bayshore Drive (Appendix B). Fecal
coliform bacteria were not sampled at this creek during the past year. Nutrient
concentrations were normally low, and phytoplankton biomass was low with only one
minor algal bloom noted, in May 2003 at PC-BDUS (Table 10.1). Median inorganic
nitrogen-to-phosphorus molar ratios were near or slightly below 16, indicating that phytoplankton growth in this creek is probably nitrogen limited. 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 10.1. Selected water quality parameters in lower Pages Creek as mean
(standard deviation) / range, August 2002-July 2003.
_____________________________________________________________________
Parameter PC-M PC-BDDS PC-BDUS
_____________________________________________________________________
Salinity (ppt) 33.8 (2.2) 27.5 (8.6) 19.9 (9.6)
27.6-36.2 3.3-36.0 3.0-32.2
Turbidity (NTU) 6 (5) 7 (4) 8 (6) 2-17 2-17 3-22
DO (mg/L) 8.2 (2.1) 7.4 (2.5) 7.8 (2.7)
5.5-11.3 4.5-11.3 4.0-11.7
Nitrate (mg/L) 0.008(0.003) 0.015(0.009) 0.015(0.008)
0.003-0.014 0.003-0.032 0.002-0.026
Ammonium (mg/L) 0.019(0.012) 0.039(0.046) 0.049(0.029)
0.001-0.045 0.001-0.163 0.018-0.100
Phosphate (mg/L) 0.004(0.002) 0.008(0.008) 0.012(0.008)
0.001-0.007 0.001-0.031 0.001-0.029
Mean N/P Ratio 22 22 19 median 17 13 13
Chlor a (µg/L) 1.4 (0.9) 4.1 (3.7) 7.5 (10.3)
0.4-3.1 0.3-10.0 0.6-36.7
_____________________________________________________________________
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 five of 11
occasions at SC-23 and four of 11 occasions at SC-CH, which was worse than the
previous year (Mallin et al. 2003). Thus, low dissolved oxygen continued to be a water quality problem in Smith Creek (Appendix B). The North Carolina turbidity standard for
estuarine waters (25 NTU) was exceeded on three of 11 occasions at SC-CH and two
of 11 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.
Total nitrogen concentrations increased over last year (Table 11.1), but algal
blooms exceeding the state standard were not found in 2002-2003, an improvement
over the previous year (Mallin et al. 2003). Fecal coliform bacteria concentrations were
above 200 CFU/100 mL on five of 11 occasions at SC-23 and four of 11 occasions at SC-CH, which was worse than the previous year (Mallin et al. 2003). The geometric
mean fecal coliform concentration was above the human contact standard at SC-23,
and both stations but well above the shellfishing standard (14 CFU/100 mL) in the
estuarine portion of the creek (Table 11.1). BOD5 was sampled on 11 occasions in
2002-2003 at SC-CH, with a mean value of 1.5 mg/L and a median value of 1.6 mg/L, a decrease over last year.
Table 11.1. Selected water quality parameters in Smith Creek watershed as mean (standard deviation) / range. August 2002 - September 2003.
_____________________________________________________________________
Parameter SC-23 SC-CH
_____________________________________________________________________
Salinity (ppt) 1.3 (2.6) 2.9 (5.3)
0.1-7.8 0.1-15.7
Dissolved oxygen (mg/L) 6.1 (2.4) 6.3 (2.5)
3.6-10.5 4.0-11.2
Turbidity (NTU) 18 (12) 24 (13)
9-43 8-54
TSS (mg/L) 13.1 (7.1) 24.0 (17.2) 1.3-26.9 1.5-49.1
Nitrate (mg/L) 0.124 (0.100) 0.159 (0.139)
0.017-0.296 0.019-0.437
Ammonium (mg/L) 0.125 (0.113) 0.100 (0.076)
0.010-0.440 0.040-0.300
Total nitrogen (mg/L) 1.236 (0.545) 1.343 (0.357)
0.737-2.726 0.737-2.060
Phosphate (mg/L) 0.078 (0.191) 0.053 (0.032)
0.006-0.651 0.012-0.121
Total phosphorus (mg/L) 0.207 (0.428) 0.091 (0.035) 0.009-1.487 0.040-0.166
Mean N/P ratio 31.0 12.7
Median 23.6 8.4
Chlor. a (µg/L) 8.5 (8.4) 6.5 (6.1)
1.5-30.9 1.0-19.1
Fecal col. /100 mL 224 144
(geomean / range) 62-1950 33-1840
BOD5 (mg/L) NA 1.5 (0.4)
1.0-2.0
_____________________________________________________________________
12.0 Lower Cape Fear
During previous studies the Wilmington City 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 had been sampled behind the
Wilmington Police Station between 2nd and 3rd Streets (Fig. 12.1), but sampling at that location was discontinued in fall 2001.
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. Major algal blooms within the lake did not
get transported over the dam to the river through this station, and turbidities were low
as well (Table 12.1; Appendix B). Fecal coliform counts exceeded the state standard
18% of the time sampled, slightly less than last year's 33% (Appendix B). In September
2003 a fish kill occurred at this location, with >450 carcasses estimated.
Table 12.1. Water quality summary statistics (mean (standard deviation) / range) for
Wilmington Lower (LCF) Cape Fear Watershed, August 2002 - September 2003.
_____________________________________________________________________
Station DO (mg/L) Turbidity (NTU) TSS (mg/L) Fecal col (CFU/100 mL)
_____________________________________________________________________
LCF-GO 6.6 (3.1) 10 (21) 4.9 (6.9) 108
0.5-12.3 1-70 0.5-25.0 12-6800 _____________________________________________________________________
Nitrate (mg/L) Ammonium (mg/L) Phosphate (mg/L) Chlor a (µg/L)
_____________________________________________________________________
LCF-GO 0.067 (0.068) 0.201 (0.180) 0.042 (0.041) 9.7 (6.7)
0.001-0.230 0.037-0.660 0.008-0.135 0.8-24.1
_____________________________________________________________________
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 on two of 12 occasions at WC-MB and
WC-AB in 2002-2003 (Table 13.1). Turbidity was within state standards for tidal waters
on all sampling occasions except for July 2003 at WC-MLR (Appendix B). There were
no 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), similar to previous years. Ammonium levels were highest at WC-NB and
WC-SB, and these levels were the highest among all of the tidal creek stations
sampled. Phosphate concentrations were highest in the middle of the creek at WC-
MLR and WC-AB. Phosphate, ammonium and nitrate at WC-MB were highest among
all creek mouth stations in the tidal creek system. Fecal coliform bacteria counts exceeded the state human contact standard during 17% of sampling occasions at WC-
MLR, 50% at WC-SB, and 75% at WC-NB. Based on fecal coliform counts and Federal
standards, in 2002-2003 shellfishing would likely have been unsafe at all stations
except at the mouth, WC-MB (Table 13.3). Whiskey Creek is presently closed to
shellfishing by the N.C. Division of Marine Fisheries.
Table 13.1. Water quality summary statistics for Whiskey Creek, August 2002-July
2003, as mean (st. dev.) / range.
Salinity Dissolved oxygen Turbidity Chlor a
(ppt) (mg/L) (NTU) (µg/L) _____________________________________________________________________
WC-MB 29.0 (4.0) 7.4 (2.4) 7 (4) 2.7 (2.9)
23.0-35.1 4.3-11.8 2-13 0.6-11.7
WC-AB 25.2 (5.7) 7.5 (2.5) 11 (6) 3.2 (3.5) 18.3-34.2 4.5-12.2 3-25 0.5-13.5
WC-MLR 20.4 (8.4) 7.5 (2.5) 15 (9) 4.5 (5.4)
8.5-32.5 4.6-12.1 5-33 1.0-20.4 WC-SB 0.2 (0.02 7.9 (1.3) 9 (7) 1.0 (0.9)
0.1-0.9 6.4-10.3 3-28 0.2-3.2
WC-NB 0.2 (0.0) 7.8 (1.9) 10 (4) 0.3 (0.2) 0.1-0.2 5.1-10.9 5-17 0.1-0.9
Table 13.2. Nutrient concentration summary statistics for Whiskey Creek, August 2002-July 2003, 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 0.028 (0.020) 0.049 (0.053) 0.008 (0.006) 30
0.006-0.070 0.005-0.202 0.001-0.021 23
WC-AB 0.037 (0.028) NA 0.009 (0.007) NA 0.009-0.097 0.001-0.027
WC-MLR 0.049 (0.029) 0.072 (0.080) 0.009 (0.005) 59
0.011-0.088 0.012-0.308 0.001-0.019 28
WC-SB 0.089 (0.069) 0.106 (0.048) 0.002 (0.003) 376
0.039-0.294 0.025-0.194 0.001-0.011 392
WC-NB 0.214 (0.062) 0.150 (0.053) 0.007 (0.006) 367
0.156-0.372 0.088-0.289 0.001-0.018 127 _____________________________________________________________________
Table 13.3 Fecal coliform concentrations in Whiskey Creek, 2002-2003. Presented as
geometric mean and range, and percent of samples >43 CFU/100 mL.
_____________________________________________________________________
Station WC-MB WC-AB WC-MLR WC-SB WC-NB
Geomean 8 (1-63) 47 (11-142) 82 (21-260) 134 (10-2000) 366 (4-3250)
%> 43 8% 58% 75% 58% 83%
_____________________________________________________________________
14.0 Fecal contamination of tidal creek sediments – links to sediment phosphorus?
Lawrence B. Cahoon and Byron Toothman Dept. of Biological Sciences
UNC Wilmington
910-962-3706, Cahoon@uncw.edu
Introduction
Fecal contamination of coastal waters is one of the most serious and well known
forms of pollution in our region, mandating closure of large areas to shellfishing and
creating a potential human health threat. In addition to shellfishing closures in estuarine
waters mandated by the N.C. Division of Shellfish Sanitation’s routine sampling, surveys of tributaries to New Hanover County’s tidal creeks show fecal contamination
levels, expressed as counts of fecal coliform bacteria (Colony Forming Units (CFU)/100
ml) that often exceed designated use standards (Mallin et al., 2002). Much of the
developed area of New Hanover County is served by a central sewage system that has
been relatively well tested and refined since its installation, so animal wastes in storm water runoff are probably the most common cause of fecal contamination in tidal creek
waters. However, fecal coliform contamination even in the absence of storm events and
their immediate runoff argues for persistence of these bacteria in tidal creek
ecosystems.
Studies of fecal coliform bacteria in coastal ecosystems have shown that levels
of these indicator bacteria in sediments may reach very high concentrations, and are
apparently maintained by favorable conditions (Rittenberg et al., 1958; Dale, 1974;
Hood and Ness, 1982; Chamroux and Guichaou, 1987; Davies et al., 1995). Our
preliminary data from the Bradley Creek drainage showed fecal coliform levels on the order of 106 CFU m-2 of sediment. These observations suggested that fecal coliform
bacteria may have a natural refuge in tidal creek sediments, where they are shielded
from harmful solar radiation, obtain needed nutrients, and find surfaces on which to
attach and survive or even grow (Dale, 1974; Tate, 1978; Henis, 1987). Furthermore,
even minor sediment disturbance may suspend sufficient numbers of sediment-associated fecal coliforms to cause non-attainment of use standards, even if no “new”
fecal coliforms have been washed into the system (Doyle, 1985; Gary and Adams,
1985; Seyfried and Harris, 1986; Palmer, 1988; Struck, 1988; Pettibone et al., 1996).
Clearly, if such a source of fecal bacterial contamination is prevalent in our coastal
ecosystems, restoration of full use of these waters will be very difficult.
Recent research has shown that not all estuarine sediments support dense
populations of fecal coliform bacteria, so some factor(s) in addition to recruitment must
act to control the actual fecal coliform content of estuarine sediments (Dale, 1974;
Hood and Ness, 1982; Chamroux and Guichaou, 1987; Davies et al., 1995). Rowland (2002) found that sediment phosphate levels were important in controlling fecal coliform
bacteria survival and growth in estuarine sediments. Phosphate loading to estuarine
waters is driven by storm water runoff and other sources that covary with fecal coliform loading. Cahoon (2002) showed that residential use of phosphate-containing fertilizers
was a major source of phosphate to sediments in tributaries in the Bradley Creek
watershed. Consequently, fecal coliform contamination of tidal creeks in New Hanover
County may be driven by a complex relationship between storm water runoff, animal
sources of fecal matter, and phosphate (and other nutrients) from fertilizers, all associated with residential land uses.
Previous studies of these problems supported by the New Hanover County Tidal
Creeks Program have shown that sediment fecal coliforms were present at
concentrations sufficient to drive closures to shellfishing and even swimming activities if suspension into a water column 1 m deep of the observed coliforms occurred. (Fig. 1).
_____________________________________________________________________
Figure 1. Plot of concentration of fecal coliforms if sediment coliforms were suspended in
a 1 m deep water column vs. sampling date (June 21 2001 to January 19 2002). Lines at
concentrations = 200 and 14 CFU/100 ml denote NC standards for human contact and shellfishing, respectively.
_____________________________________________________________________
We continued the investigation of linkages between sediment phosphorus and
sediment fecal coliform bacteria levels in New Hanover County’s tidal creeks. The
issues posed by these linkages obviously have larger implications and pose broader
questions than can be addressed by a relatively limited project, but one significant and appropriate question has been addressed in this study: Do sediment phosphorus levels
show any correlation with sediment fecal coliform levels?
Methods
Sampling sites were located in the Bradley Creek drainage, using locations previously sampled so as to maintain continuity (Fig. 2). These locations were sampled
at least monthly for sediment phosphorus, sediment fecal coliforms, temperature and
salinity. The top 2.0 centimeters of estuarine sediments were cored at each site. Three
sediment cores were taken randomly at each site using sterile 2.20 cm ID acrylic tubing
for sediment fecal coliform analyses. Following methods developed by Rowland (2002), each sample was transferred to a previously weighed, sterile 50ml polypropylene
centrifuge tube and placed on ice. The three samples were each mixed with 1L of
Figure 2. Map showing sampling locations in the Bradley Creek watershed, named
for nearby streets or tributaries. A=Andover (BC-SBU), CR=Clear Run (BC-CA),
E=Eastwood (BC-NBU), M=Mallard (BC-CR), S=Softwind (BC-SB), W=Wrightsville
(BC-NB). North is up. See also Fig. 7.1.
_____________________________________________________________________
sterile phosphate-buffered rinse water inside a sterile 1L flask with a stir bar. Each sample was gently stirred for 2 minutes prior to performing the membrane filtration
technique. From the mixture of sterile phosphate-buffered rinse water and sediment,
three 10 ml and three 1 ml samples were used for fecal coliform analysis using
standard methods for membrane filtration of fecal coliform bacteria, method 9.222
(APHA, 1998). The sediment and rinse water solution were mixed before each sample withdrawal to reduce fecal coliform burial and homogenize the bacteria suspension. All
plates were incubated in a water bath for 24 hours at 44.5° C. After the 24-hour
incubation period, each plate was inspected for dark blue colonies. Each dark blue
colony represented one colony-forming unit (CFU). Counts from each 10ml sample
from each of the three cores from each site were averaged and expressed as the number of colony forming units per square centimeter (CFU cm-2) + one std. dev.
Sediment phosphate was analyzed on a second triplicate set of sediment cores
taken randomly at each sampling site simultaneously with fecal coliform samples. Sub-
samples of dried sediments were weighed and analyzed for phosphate content following digestion with the persulfate-boric acid method of Valderrama (1981). This
method oxidizes relatively labile forms of phosphorus to orthophosphate, and likely
represents reasonably accurately the bio-available phosphorus in sediments, in contrast
to more robust extraction and digestion methods that likely quantify additional
phosphorus that may be less bio-available. Sediment phosphate content was expressed as ug P (g sediment)-1.
Results
The concentrations of fecal coliform bacteria in sediments of Bradley Creek were
highly variable, ranging from values of 0 to over 3,000 CFU cm-2 in a total of 65 samples collected between January and November, 2003. The arithmetic mean value
observed was 265 CFU cm-2 overall, which corresponds to a value of 265 CFU per 100
mls if all these bacteria were suspended in a water column 1 meter deep, a value high
enough to close the water to human body contact. The standard for shellfishing is much
lower, 14 CFU per 100 mls; 49 of the 65 samples exceeded this value using analogous assumptions. Mean values for the respective sampling sites were similarly higher than
the human body contact standard, except for the site at Clear Run Branch (BC-CR,
“CR” in Fig. 2) (Table 1). Thus, the levels of fecal coliform bacteria measured in Bradley
Creek’s sediments frequently represent serious potential problems for human uses of
these waters.
Table 1. Concentrations of fecal coliform bacteria in sediments at sampling sites within the Bradley Creek drainage, CFU cm-2. Site designations as in Fig. 2.
Site A CR E M S W Mean 303 40 418 429 250 145
Range 2.5-1630 0-234 20.3-1660 10.2-3271 7.6-1820 0-325
There was no clear relationship between sediment fecal coliform bacteria concentrations and sediment phosphorus levels (Fig. 3). Occasional high values of
sediment fecal coliforms occurred across most of the concentration range for sediment
phosphorus, as did low values of sediment fecal coliforms. If there is a relationship
between the two parameters, it may require a much larger data set and/or more
elaborate analysis of multiple variables to detect it.
Fig. 3. Bradley Creek sediment fecal coliforms vs. sediment phosphorus concentrations.
Although an effect of salinity, either as a stressor for fecal bacteria or as a proxy for
distance or transit time from their warm-blooded host sources, was expected, no clear
relationship was detected between these two parameters, either (Fig. 4).
Fig. 4. Bradley Creek sediment fecal coliforms vs. salinity.
Again, additional data and more sophisticated analysis would help resolve any
relationship if one exists.
Temperature appeared to have had an effect on the concentrations of sediment fecal
bacteria. Fecal bacteria concentrations were lowest at low temperatures and generally
Fig. 5. Bradley Creek sediment fecal coliforms vs. water temperature.
highest at intermediate temperatures. Very low temperatures are known to limit growth rates of fecal coliform bacteria, which grow optimally at the body temperatures of warm-blooded host organisms. High temperatures may be stressful in the absence of
sufficient nutrients and organic substrates.
Additional data and analysis will be required to evaluate interactions of the factors considered above in controlling the concentrations of sediment fecal coliform bacteria. It is also likely that other parameters, such as the availability of labile organic
substrates, may be important.
Discussion Sediments in the Bradley Creek drainage frequently harbored significant
populations of fecal coliform bacteria, particularly during the warmer times of the year
when children are most likely to play in these waters. As other studies have shown that
fecal coliform bacteria concentrations in sediments do indicate the presence of other fecal pathogens (Rittenberg et al., 1958; Lipp et al., 2001), it is important to consider the public health risk associated with this poorly known reservoir of contaminants. Many
water-borne diseases are not properly tracked to their sources, so a significant problem
may be occurring without real awareness of its cause.
Given the attributes of the Bradley Creek watershed, it is likely that animals, both wild and domestic, were the most important fecal contamination sources. One
conclusion, therefore, is that pet waste management should be addressed for all residential areas in coastal watersheds, not just beach communities. Moreover, a
significant population of “wildlife” that actually associates with human communities,
eating human garbage and unsecured pet foods, such as raccoons and opossums,
likely lives in this watershed and contributes to the fecal contamination problem.
Educational efforts can reduce this problem as well. It is important to note that animal wastes can be as dangerous a source of pathogens to humans as human waste,
particularly because some of the animal-derived pathogens, such as infectious
protozoans, can cause infections that are difficult to diagnose and treat. For example,
an AP story published recently in the Wilmington Star-News discussed how infections
from a widely distributed pathogenic amoeba, Naegleria fowleri, have caused fatal brain
inflammations in swimmers.
Data generated by this effort and the previous study (Rowland 2002), which
provided the data in Fig. 1, have also supported a successful proposal to UNC Sea
Grant for a much more thorough study of the main hypothesis and other issues
addressed in this study. This research project will begin in February, 2004, and will include an effort to examine a much larger suite of parameters that may affect fecal
coliform concentrations in tidal creek sediments.
Literature Cited
APHA. 1998. Standard methods for the examination of water and waste water, 20th ed.
American Public Health Association. Washington, D.C., A.E. Greenberg, ed.
Cahoon, L.B. 2002. Residential land use, fertilizer, and soil phosphorus as a phosphorus
source to surface drainages in New Hanover County, North Carolina. Journal of the N.C. Academy of Science 118(3):156-166.
Chamroux, S. and C. Guichaou. 1987. The role of sediment in maintaining the
presence of pollution in coastal waters. Ecological Management Of The Sea 14:45-
49.
Dale, N.G. 1974. Bacteria in intertidal sediments: factors related to their distribution.
Limnol. Oceanogr. 19:509-518
Davies, C.M., J.A. Long, M. Donald, and N.J. Ashbolt. 1995. Survival of fecal microorganisms in marine and freshwater sediments. App. Env. Microbiol. 61:1888-
1896.
Doyle, J.D. 1985. Analyses of recreational water quality as related to sediment
resuspension. Dissertation Abstracts International. Part B. Science and Engineering. Vol. 6, No.4 pp 79.
Gary, H.L. and J.C. Adams. 1985. Indicator bacteria in water and stream sediments
near the Snowy Range in Southern Wyoming. Water Air Soil Pollut. 25:133-144.
Henis, Y, ed. 1987. Survival and dormancy of microorganisms. New York: John
Wiley and Sons. Pp.1-35.
Hood, M.A., and G.E. Ness. 1982. Survival of Vibrio cholerae and Escherichia coli in
estuarine waters and sediments. Appl. Environ. Microbiol. 43:578-584.
Lipp, E.K., R. Kurz, R. Vincent, C. Rodriguez-Palacios, S.R. Farrah, and J.B. Rose.
2001. The effects of seasonal variability and weather on microbial fecal pollution and enteric pathogens in a subtropical estuary. Estuaries 24:266-276.
Mallin, M.A., L.B. Cahoon, M.H. Posey, L.A. Leonard, D.C. Parsons, V.L. Johnson, E.J.
Wambach, T.D. Alphin, K.A. Nelson, and J.F. Merritt. 2002. Environmental quality of
Wilmington and New Hanover County watersheds. CMS Report 02-01.
Palmer, M. 1988. Bacterial loadings from resuspended sediments in recreational
beaches. Can. J. Civ. Eng. 15:450-455.
Pettibone, G.W., K.N. Irvine, and K.M. Monohan. 1996. Impact of a ship passage on
bacteria levels and suspended sediment characteristics in the Buffalo River, New York. Water Res. 30:2517-2521.
Rittenberg, S.C., T. Mittwer, and O. Ivier. 1958. Coliform bacteria in sediments around
three marine sewage outfalls. Limnol. Oceanogr. 3:101-108.
Rowland, K.R. 2002. Survival of sediment-bound fecal coliform bacteria and potential
pathogens in relation to phosphate concentration in estuarine sediments. Unpublished
M.S. thesis, UNC Wilmington, Wilmington, N.C.
Seyfried, P.L., and E.M. Harris. 1986. Detailed bacteriological water quality study examining the impact of sediment and survival times. Technology Transfer
Conference. Part B: Water Quality Research. pp. 347-391.
Struck, P.H. 1988. Relationship between sediment and fecal coliform levels in a Puget
Sound Estuary. J. Env. Health. 50:403-407.
Tate, R.L., III. 1978. Cultural and environment factors affecting the longevity of
Escherichia coli in Histosols. Appl. Environ. Microbiol. 35:925-929.
Valderrama, J.C. 1981. The simultaneous analysis of total nitrogen and phosphorus in natural waters. Mar. Chem. 10:109-122.
15.0 Studies of Oyster Reefs in New Hanover County Tidal Creeks
Martin Posey, Troy Alphin, Heather Harwell, Bethany Noller
I. Overview
The UNCW Benthic Ecology Lab has conducted several projects to evaluate the
ecosystem health of New Hanover tidal creeks, with partial support from North Carolina
Sea Grant, NC Fisheries Resource Grant Program, the UNCW Center for Marine
Science, and the New Hanover County Tidal Creeks Program. Among the major areas of emphasis for these studies are oyster communities and their ecosystem functions in
New Hanover County tidal creeks. In previous studies we have examined the effect of
establishing oyster reefs in small tributary creeks on water column nutrients, suspended
solids, chlorophyll a and aspects of faunal use (Nelson et.al. 2004; Alphin and Posey,
unpublished data). Ongoing projects include studies of reef complexity and patch reef size effects on oyster ecosystem function. As part of a project partially supported by the New Hanover Tidal Creeks Program, we are also currently evaluating the percent cover
and total cover of oysters in lower Pages, Hewletts, Howe and Whiskey Creeks. We
have recently begun using archived digital images to evaluate current and historic
oyster coverage among the tidal creeks (images provided by the New Hanover County Planning office), coupled with field assessment of oyster reef health based on morphological characteristics of the oyster reefs themselves. This report presents
information from several years of field sampling concentrating on aspects of reef
structural complexity, uniformity and oyster density that may influence their role as
habitat and 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 functions 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
Oyster populations along the east coast have been experiencing sharp declines
throughout much of their range (Hargis 1999, Breitberg et al. 2000, Mann 2000). This
decline has been blamed on three primary factors; overfishing, disease, and loss of habitat (due in part to increases in coastal development). As this decline has progressed over the last four decades, researchers and managers have recognized the
importance of oysters as habitat for other fisheries species and for intrinsic ecosystem
functions beyond their role as a harvestable resource. However, researchers and
resource managers have only recently begun to understand how important oyster reefs are 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 a greater value to the local communities
than the simple market value of the harvested oysters. 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 in the Chesapeake Bay (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
directly relates to effects on smaller prey species as well as indirect and direct effects
on larger fish and decapods that may be intermediate or top predators within these
smaller estuarine systems. 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 numbers in open
sandflats where predatory fish and crabs have greater access. 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 suspended particulates, water column chlorophyll and water
column nutrients before reefs were decimated by disease and over harvesting. 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 (habitat complexity), density of live
oysters, and vertical relief of shells (maximum height above the underlying substrate). Understanding how these characteristics of oyster reefs vary among the New Hanover
County tidal creek systems is critical for assessing current health of oysters in these
systems as well as for management planning related to oyster restoration.
III. Methods
Two to three intertidal oyster reefs randomly selected in the lower portion of
Pages, Howe, Hewletts and Whiskey Creeks were sampled in 2001 and 2003. All reefs
selected had a diameter of at least 3m (but not more that 6m) and were separated from
sources of disturbance such as channels by at least 10m. Regions of the creeks with active marinas were also avoided.
Percent shell cover, presence of shell hash, and live oyster density were
measured in replicate 30 cm x 30 cm quadrats. Ten randomly placed quadrat samples
were taken within each of the selected reefs. All quadrat samples were at least 0.5m within the reef to reduce edge effects. Percent oyster cover was determined by the
point intercept method. Five monofilament lines were strung at right angles over the
quadrat creating 25 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. Information on the presence and type (broken shell vs 3 dimensional culms) of shell hash may be important as habitat for cryptic fish, crabs and
shrimp. A quadrat was 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 structure may have led to some under representation of new recruits.
During the 2001 sampling period vertical relief of the oyster bed was defined as
the height of shells (culms) above the underlying sand substrate. Ten 50 cm X 50 cm
quadrats were selected on each reef. Each quadrat was divided into 25 equal squares creating 16 intercept points defined by the intersection of four equally spaced lines set
perpendicular to each other. The vertical height of shell underlying each of the 16
points was measured from the substrate surface to the highest point within 1 cm
diameter of the intersection point. During subsequent sampling events in 2003, vertical
complexity of oyster reefs was measured using the chain method (a ratio of the straight line distance to vertical contour). Ratios approaching zero indicate extreme complexity
while ratios approaching 1 indicated virtually no complexity. Vertical complexity values
for this region are commonly in the 0.6-0.7 range, whereas values of 0.9 are low. The
chain method gives a better estimation of the amount of vertical complexity within the
reef structure and has been applied in other reef habitats (e.g. coral reefs). In addition to the chain measurement, absolute height of the oyster culms was also measured in
2003. This data was collected by measuring from the substrate surface to the highest
point on the oyster culms. Qualitative data on the presence of algal cover (if algal
growth covered greater than 25% of the total area of the reef, it may negatively impact
the development of healthy oyster reefs), sedimentation (sediment coverage of the > 10% of the total reef area), percent shell hash coverage, and percent open area
(percent cover determined as defined above).
IV. Results
Here we present data from both 2001 and 2003. During the 2001 sampling year
we collected data from 4 of the tidal creeks (Pages, Howe, Hewletts, and Whiskey) as a
broad survey of the tidal creeks within the county. During 2003 we focused on collecting data from two target creeks (Hewletts and Pages) that were the subject of
other studies evaluating utilization of oyster reefs based on physical characteristics.
During 2001, percent shell cover 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).
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. 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). 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). During 2003
percent shell cover at Hewletts and Pages Creeks showed a disconcerting trend
towards loss of well-developed structure, with shell cover comprised primarily of shell
harsh with very few 3 dimensional culms (Figure 1).
During 2001, 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 were 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 were 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 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. Evaluation of live oyster density in
Hewletts and Pages during 2003 indicated a decline since 2001 (Figure 2). This
decline in live oyster density coincides with a decline in the amount of 3 dimensional
oyster culms (Figure 1), such that most of the shell coverage for this sampling period was nearly all broken shell hash.
Assessment of vertical height of oyster reefs conducted in 2001 was greatest in
Howe Creek (Figure 3) and intermediate in Pages Creek. Average vertical relief was
low in both Hewletts and Whiskey Creeks. Vertical height presented here is the greatest
height of oysters above the substrate and not average reef height overall. As such, it is a measure of the presence of well-developed oyster culms.
0
20
40
60
80
100
120
Pages Pages 2002 Howe Hewletts Hewletts 2002 Whiskey
Figure 1: Shell Coverage Within Oyster Reefs. % bottom area represents mean
shell cover per 0.09 m2 quadrat (+1SE). % of quadrats with shell hash indicates
total percent of all quadrats with >10% shell has cover.
Pe
r
c
e
n
t
% of bottom covered by shell
% of quadrats with shell hash
0
5
10
15
20
25
Pages Pages 2002 Howe Hewletts Hewletts 2002 Whiskey
Figure 2: Density of Live Oysters Within Reefs. Bars indicate Number live
oysters per 0.09 m2 (+1 SE).
No
.
p
e
r
0
.
0
9
m
2
In 2003 assessments of oyster reefs for both Pages and Hewletts Creeks were
conducted in much the same way as earlier assessments. However measurements of vertical relief using the chain method were collected in addition to measurements of
absolute height. The chain method provides a better estimate of vertical complexity
and so allows for a better understanding of the habitat quality of the oyster reefs in
question. In addition to the relief measurements we also collected qualitative data on
coverage (% open mud, % actual shell hash), sedimentation, and presence of significant algal cover (>25% of the total reef area). All of which are factors that may
impact the overall function of the oyster habitat and will allow inferences as to whether
the reefs are in a state of growth or decline.
Measurements of vertical complexity in 2003 show that reefs in both Pages and Hewletts Creeks seem to have similar vertical profiles with average complexity
measurements in Hewletts Creek ranging from 0.71 to 0.85 (Table 1) and Pages Creek
ranging from 0.52 to 0.77 (Table 2). (Note that a complexity value of 1 would indicate
the reef had no vertical relief). There was high variability in the amount of shell hash
present among the various reefs for both creeks, although algal cover did not seem to be a significant problem and sedimentation was only noted at two reefs in Hewletts
Creek (Table 1 and Table 2).
0
1
2
3
4
5
6
7
8
Pages Howe Hewletts Whiskey
Figure 3: 2001 Vertical relief within reefs. Bars indicate vertical relief of shells
(measured from underlying sand substrate) (+1 SE).
Re
l
i
e
f
(
c
m
)
Table 1. Shell cover, oyster density and
physical parameters of oyster reefs in
Hewletts Creek during 2003.
Reef 1 Reef 2 Reef 3 Reef 4
Average % open 35.5 46.8 81.3 44.6
Average % Shell Hash 56.6 23.2 9.5 39
Avg # Live Oysters/400 cm2 5 6.2 2.3 5.5
Avg Vertical Complexity 0.71 0.85 0.76 0.79
Algal cover >25% no No No Yes
Sedimentation no Yes Yes No
Highest Point (cm) 21.5 19 32 20
Table 2. Shell cover, oyster
density and physical
parameters of oyster reefs in Pages Creek during 2003.
Reef 1 Reef 2 Reef 3
Average % open 52 16 5
Average % Shell Hash 28 28 75
Avg # Live Oysters/400 cm2 4.9 11.8 5.2
Avg Vertical Complexity 0.77 0.52 0.64
Algal cover >25% No No No
Sedimentation No No No
Highest Point (cm) 20 20 22
Conclusions
These results suggest considerable variability in oyster reef characteristics
among the New Hanover tidal creeks examined. In 2001 Pages Creek was described
as having “high shell coverage, relatively high densities of live oysters (compared to
other creeks examined), and intermediate vertical relief”, while Hewletts Creek was defined as intermediate among the four creeks overall with “relatively high live oyster
densities, but low relief”. As noted previously live oyster densities in Pages and
Hewletts Creeks were greater than measurements in Howe or Whiskey Creeks during
2001 but declined in the 2003 measurements. This is a source of some concern
because we also recorded an increase in the amount of shell hash coverage compared to total oyster shell coverage (culms + shell hash) (Figure 1). Our concern here is that
this change may reflect a decline in the oyster populations within these areas. Data
from an associated project looking at settlement within the Hewletts Creek system
(during late 2002 and early 2003) shows that larvae did recruit to that system,
suggesting that factors other than larval supply may be primarily responsible for this pattern. Measurements of reef complexity were moderate for both Pages and Hewletts
Creeks (Tables 1-2) indicating the presence of some high relief culms. Although these
same data showed that the amount of open space within reefs at these two creeks was
variable, with some reefs having >50% of the area within the reef as open space.
These data would seem to indicate that reefs in these two systems demonstrate a high degree of variability among years and give some indication of the dynamic nature of
oyster reef formation. In many cases the most complex oyster habitats may be those
that provide both oyster structure and open patches within the reef proper. The
question that we must now focus on is at what point do oyster reefs provide the greatest
benefits to other organisms (as habitat, refuge, and as system modifiers) while still providing the aggregate needs for healthy oysters and good settlement structure for
larvae to maintain the reef integrity.
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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.
Mallin, M.A., L.B. Cahoon, M.H. Posey, L.A. Leonard, D.C. Parsons, V.L. Johnson, E.J.
Wambach, T.D. Alphin, K.A. Nelson and J.F. Merritt. 2002a. Environmental Quality
of Wilmington and New Hanover County Watersheds, 2000-2001. CMS Report 02-
01, Center for Marine Science, University of North Carolina at Wilmington, Wilmington, N.C. Mallin, M.A., S.H. Ensign, T.L. Wheeler and D.B. Mayes. 2002b. Pollutant removal efficacy of three wet detention ponds. Journal of Environmental Quality 31:654-660.
Mallin, M.A., L.B. Cahoon, M.H. Posey, D.C. Parsons, V.L. Johnson, T.D. Alphin and
J.F. Merritt. 2003a. Environmental Quality of Wilmington and New Hanover County
Watersheds, 2001-2002. CMS Report 03-01, Center for Marine Science, University
of North Carolina at Wilmington, Wilmington, N.C. Mallin, M.A., H.A. CoVan and D.H. Wells. 2003b. Water Quality Analysis of the Mason Inlet Relocation Project. CMS Report 03-02. Center for Marine Science, University of North Carolina at Wilmington, Wilmington, N.C.
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.
Roberts, T.L. 2002. Chemical constituents in the Peedee and Castle Hayne aquifers: Porter’s Neck area, New Hanover County, North Carolina. M.S. Thesis, Department of Earth Sciences, University of North Carolina at Wilmington, Wilmington, N.C. 63 p
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
Estuarine Environmental Matrices, 2nd Ed. EPA/600/R-97/072. National Exposure Research Laboratory, Office of Research and Development, U.S. Environmental
Protection Agency, Cincinnati, Ohio.
Welschmeyer, N.A. 1994. Fluorometric analysis of chlorophyll a in the presence of
chlorophyll b and phaeopigments. Limnology and Oceanography 39:1985-1993.
17.0 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 Dexter Hayes, Matt Hayes, David Mayes, Chris O’Keefe, Rick Shiver and Dave Weaver. For field and laboratory assistance we thank Kim
Cressman, Brian Farlow, Heather Harwell, Matthew McIver, Tara MacPherson,
Bethany Noller, Byron Toothman, Heather Wells, and Kevin Woodward.
18.0 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
19.0 Appendix B. UNCW ratings of sampling stations in Wilmington and New Hanover County watersheds based on August 2002 – July 2002 data (tidal creeks); August 2002
– September 2003 (Wilmington watersheds), where available, for chlorophyll a,
dissolved oxygen, turbidity, and fecal coliform bacteria based on North Carolina state
chemical standards for freshwater or tidal saltwater.
_____________________________________________________________________
G (good quality) – state standard exceeded in < 10% of the measurements F (fair quality) – state standard exceeded in 11-25% of the measurements
P (poor quality) – state standard exceeded in >25% of the measurements
_____________________________________________________________________
Watershed Station Chlor a DO Turbidity Fecal coliforms*
Barnard’s Creek BNC-TR G F F P BNC-CB G G G P BNC-RR G P P F
Bradley Creek BC-CA G F G P
BC-CR G G G - BC-SB G G F - BC-SBU G G G -
BC-NB G F G -
BC-NBU G G G -
BC-76 G G G - Burnt Mill Creek BMC-AP1 G F G P
BMC-AP3 G G G P
BMC-PP G P G P
Futch Creek FC-4 G G G G FC-6 G G G G
FC-8 G G G G
FC-13 G G G G
FC-17 G F G G FOY G G G G
Greenfield Lake GL-SS1 G P G P
GL-SS2 G G G P
GL-LC G P G P GL-JRB G P G P GL-LB G P G P
GL-2340 G P G P
GL-YD G P G P
GL-P G P G P
Hewletts Creek PVGC-9 G G G P HC-M G G G -
HC-2 G G G -
HC-3 G G G -
HC-NWB G G G -
NB-GLR G G F - MB-PGR G G G -
SB-PGR G G G -
Howe Creek HW-M G G G G
HW-FP G G G G HW-GC G F G F
HW-GP G F G F
HW-DT G G G P
Motts Creek MOT-RR G P P P
Pages Creek PC-M G G G -
PC-BDDS G F G -
PC-BDUS G F G -
Smith Creek SC-23 G P F P
SC-CH G P P P
Lower Cape Fear LCF-GO G F G F
Whiskey Creek WC-NB G G G P
WC-SB G G G P
WC-MLR G G F F
WC-AB G F G G
WC-MB G F G G _____________________________________________________________________
* 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.
20.0 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 34.16823 W 77.93218
BNC-CB N 34.15867 W 77.91190 BNC-EF N 34.16937 W 77.92485
BNC-AW N 34.16483 W 77.92577
BNC-RR N 34.15873 W 77.93795
Bradley Creek BC-CA N 34.23257 W 77.86658 BC-CR N 34.23077 W 77.85235
BC-SB N 34.21977 W 77.84578
BC-SBU N 34.21725 W 77.85410
BC-NB N 34.22150 W 77.84405
BC-NBU N 34.23265 W 77.92362 BC-76 N 34.21473 W 77.83357
Burnt Mill Creek BMC-AP1 N 34.22927 W 77.86658
BMC-AP2 N 34.22927 W 77.89792
BMC-AP3 N 34.22927 W 77.90143 BMC-PP N 34.24252 W 77.92510
Futch Creek FC-4 N 34.30127 W 77.74635
FC-6 N 34.30298 W 77.75070
FC-8 N 34.30423 W 77.75415 FC-13 N 34.30352 W 77.75790
FC-17 N 34.30378 W 77.76422
FOY N 34.30705 W 77.75707
Greenfield Lake GL-SS1 N 34.19963 W 77.92447 GL-SS2 N 34.20038 W 77.92952
GL-LC N 34.20752 W 77.92980
GL-JRB N 34.21260 W 77.93140
GL-LB N 34.21445 W 77.93553
GL-2340 N 34.19857 W 77.93560 GL-YD N 34.20702 W 77.93120
GL-P N 34.21370 W 77.94362
Hewletts Creek PVGC-9 N 34.19165 W 77.89175
HC-M N 34.18230 W 77.83888
HC-2 N 34.18723 W 77.84307
HC-3 N 34.19023 W 77.85083
HC-NWB N 34.19512 W 77.86155 NB-GLR N 34.19783 W 77.86317
MB-PGR N 34.19807 W 77.87088
SB-PGR N 34.19025 W 77.86472
Howe Creek HW-M N 34.24765 W 77.78718 HW-FP N 34.25443 W 77.79488
HW-GC N 34.25448 W 77.80512
HW-GP N 34.25545 W 77.81530
HW-DT N 34.25562 W 77.81952
Motts Creek MOT-RR N 34.15867 W 77.91605
Pages Creek PC-M N 34.27008 W 77.77133
PC-OL N 34.27450 W 77.77567
PC-CON N 34.27743 W 77.77763 PC-OP N 34.28292 W 77.78032
PC-LD N 34.28067 W 77.78495
PC-BDDS N 34.28143 W 77.79417
PC-WB N 34.27635 W 77.79582
PC-BDUS N 34.27732 W 77.80153 PC-H N 34.27508 W 77.79813
Smith Creek SC-23 N 34.25795 W 77.91967
SC-CH N 34.25897 W 77.93872
Upper and Lower UCF-PS N 34.24205 W 77.94838
Cape Fear LCF-GO N 34.21230 W 77.98603
Whiskey Creek WC-NB N 34.16803 W 77.87648
WC-SB N 34.15935 W 77.87470 WC-MLR N 34.16013 W 77.86633
WC-AB N 34.15967 W 77.86177
WC-MB N 34.15748 W 77.85640
_____________________________________________________________________
21.0 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.
Hales, J. C. 2001. Tidal exchange in coastal estuaries: effects of development, rain and
dredging. M.S. Thesis, Program in Marine Science, University of North Carolina at
Wilmington, Wilmington, N.C. 46 pp.
Mallin, M.A., L.B. Cahoon, M.H. Posey, L.A. Leonard, D.C. Parsons, V.L. Johnson, E.J.
Wambach, T.D. Alphin, K.A. Nelson and J.F. Merritt. 2002. Environmental Quality of
Wilmington and New Hanover County Watersheds, 2000-2001. CMS Report 02-01,
Center for Marine Science, University of North Carolina at Wilmington, Wilmington,
N.C.
Mallin, M.A., L.B. Cahoon, M.H. Posey, D.C. Parsons, V.L. Johnson, T.D. Alphin and
J.F. Merritt. 2003. Environmental Quality of Wilmington and New Hanover County
Watersheds, 2001-2002. CMS Report 03-01, Center for Marine Science, University
of North Carolina at Wilmington, Wilmington, N.C.
Mallin, M.A., H.A. CoVan and D.H. Wells. 2003. Water Quality Analysis of the Mason
inlet Relocation Project. CMS Report 03-02. Center for Marine Science, University of
North Carolina at Wilmington, Wilmington, N.C.
Peer-reviewed UNCW journal papers concerning water quality in New Hanover County’s tidal creeks.
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. Mallin, M.A., S.H. Ensign, T.L. Wheeler and D.B. Mayes. 2002. Pollutant removal efficacy of three wet detention ponds. Journal of Environmental Quality 31:654-660. Posey, M.H., T.D. Alphin, L.B. Cahoon, D.G. Lindquist, M.A. Mallin and M.E. Nevers. 2002. Resource availability versus predator control: questions of scale in benthic infaunal communities. Estuaries 25:999-1014. Cressman, K.A., M.H. Posey, M.A. Mallin, L.A. Leonard and T.D. Alphin. 2003. Effects of oyster reefs on water quality in a tidal creek estuary. Journal of Shellfish Research 22:753-762. Mallin, M.A. and A.J. Lewitus. 2004. The importance of tidal creek ecosystems. Journal of Experimental Marine Biology and Ecology 298:145-149. Mallin, M.A., D.C. Parsons, V.L. Johnson, M.R. McIver and H.A. CoVan. 2004. Nutrient limitation and algal blooms in urbanizing tidal creeks. Journal of Experimental Marine Biology and Ecology 298:211-231. Nelson, K.A., L.A. Leonard, M.H. Posey, T.D. Alphin and M.A. Mallin. 2004. Transplanted oyster (Crassostrea virginica) beds as self-sustaining mechanisms for water quality improvement in small tidal creeks. Journal of Experimental Marine Biology and Ecology 298:347-368.