2003-2004 Final Report
ENVIRONMENTAL QUALITY OF WILMINGTON AND
NEW HANOVER COUNTY WATERSHEDS
2003-2004
by
Michael A. Mallin, Lawrence B. Cahoon, Martin H. Posey, Virginia L. Johnson,
Douglas C. Parsons, Troy D. Alphin, Byron R. Toothman and James F. Merritt
CMS Report 05-01
Center for Marine Science
University of North Carolina at Wilmington
Wilmington, N.C. 28409
January, 2005
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 11 watersheds and 50 sampling stations. In this
summary we first present brief water quality overviews for each watershed from August
2003 – July 2004, and then discuss key results of several special studies conducted
over the past two years.
Barnards Creek – There was only one station sampled in this watershed during 2004,
lower Barnard’s Creek at River Road. This site had no algal bloom or BOD problems; it
had fair water quality in terms of fecal coliform counts but poor water quality as judged
by excess turbidity and low dissolved oxygen. It also had the highest suspended solids,
ammonium, total nitrogen and total phosphorus levels among all the local watersheds.
Bradley Creek – Turbidity was not problematic during 2003-2004. Dissolved oxygen
was good to fair at all sites except the branch at College Acres (BC-CA) where it fell
below 5.0 mg/L on three occasions during summer. Elevated nitrogen and phosphorus
levels enter the creek in both the north and south branches, one minor algal bloom occurred in the south branch (BC-SB) and one major bloom occurred in the creek at
College Acres. Fecal coliform bacterial counts were only sampled at BC-CA, where
contamination was excessive during six of the seven samples collected in 2004.
Burnt Mill Creek – A sampling station on Burnt Mill Creek at Princess Place had no turbidity or suspended solids problems, but substandard dissolved oxygen during all
visits from May through September. There was one moderate algal bloom in June
2004. This station also had poor microbiological water quality, exceeding the standard
for human contact in five of seven samples. The effectiveness of Ann McCrary wet
detention pond on Randall Parkway as a pollution control device was poor during 2004. While the pond led to a significant reduction in fecal coliform bacteria and an increase
in dissolved oxygen, it failed to reduce nutrient concentrations including ammonium,
nitrate, total nitrogen, orthophosphate and total phosphorus. Several water quality
parameters indicated a subsequent worsening of the creek from where it exited the
pond to the downstream Princess Place sampling station. Fecal coliform bacteria and low dissolved oxygen are the primary problems in Burnt Mill Creek.
Futch Creek – Futch Creek maintained good microbiological water quality, as it has
since channel dredging at the mouth occurred in 1995 and 1996. Algal blooms and
turbidity were not problems in 2003-2004. Dissolved oxygen concentrations periodically decreased below 5.0 mg/L in summer at some upper creek stations, but otherwise 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. However, fecal coliform concentrations have recently shown an
increasing trend in some upper and middle creek stations, potentially a result of increasing development in the headwaters areas.
Greenfield Lake – The three tributaries of Greenfield Lake (near Lake Branch Drive, Jumping Run Branch, and Lakeshore Commons Apartments) all suffered from severe
low dissolved oxygen problems and the in-lake stations (GL-2340, GL-YD, and GL-P)
had low dissolved oxygen periodically. 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. Station GL-P, at the Park, had high fecal coliform counts on three of the seven occasions sampled, and very low dissolved oxygen during
summer. The stream near Lakeshore Commons also maintained high nitrate and
phosphate concentrations. The lake again experienced algal blooms at times, with
several blooms exceeding the N.C. State Standard of 40 µg/L of chlorophyll a, and a
three-month duckweed bloom near the Park. In general, Greenfield Lake continues to suffer from fecal coliform bacterial contamination, algal blooms, and low dissolved
oxygen problems.
Hewletts Creek – The tidally-influenced stations in this watershed had generally low
turbidity levels in 2003-2004. Two major algal blooms occurred in the north branch (NB-GLR) in summer 2004, with dissolved oxygen concentrations generally good to fair
at tidal sites. Fecal coliform counts were low at the lower sites, moderate at the mid-
creek sites, and high in terms of the N.C.human contact standard of 200 CFU/100 mL
at the north and middle branches, but moderate at the south branch.
Since January 2004 five non-tidal sites have been sampled in the Hewletts Creek
watershed. One site is PVGC-9, draining Pine Valley Country Club. This stream had
no dissolved oxygen or turbidity problems, moderate nutrient levels, and had one
severe algal bloom in summer 2004. However, six of the seven months sampled
showed excessive fecal coliform counts, a general increase over previous years. The other sites are being sampled to gain background information on the water quality of
streams entering (DB-1, DB-2, DB-3) and exiting (DB-4) a proposed constructed
wetland/future park area known as the Dobo site, draining into the headwaters of
Hewletts Creek. The input and output streams to the Dobo site had no turbidity or algal
bloom problems, but low dissolved oxygen was an issue at DB-1 and all sites had excessive fecal coliform problems. DB-1 also had comparatively high ammonium, total
nitrogen, and total phosphorus problems.
Howe Creek – Five stations were sampled in Howe Creek in 2003-2004. The lower
creek maintained good water quality. 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 mid-creek, and high in the uppermost two stations
during 2003-2004. After several years of improving water quality, in 2003-2004 the
upper two stations showed a doubling of fecal coliform counts from 2001-2003 levels.
This is a concern especially as Howe Creek was previously designated as an Outstanding Resources Water by the State of North Carolina.
Motts Creek – This creek was sampled at only one station, at River Road. One major
and one minor algal bloom occurred during this sampling period. Dissolved oxygen was
below 5.0 mg/L on all occasions from May through September and there were a few instances of elevated BOD5 in 2004. Turbidity and suspended sediments were not a
problem. Fecal coliform counts exceeded 200 CFU/100 mL on five of the seven sampling occasions in 2004.
Pages Creek – This creek maintained generally good water quality during 2003-2004.
Nutrient loading was low and algal blooms were not found, even at the most human-
impacted stations. 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 2003-2004. This watershed has some of the lowest development and
impervious surface coverage in the New Hanover County tidal creek system.
Smith Creek – Smith Creek (sampled at SC-CH, at Castle Hayne road) had moderate water quality problems as reflected by several parameters. Turbidity and elevated
suspended sediments occurred on occasion, but algal blooms or high BOD were not
problematic. Excessive fecal coliform bacteria counts occurred on two of seven
sampling occasions in 2004. Low dissolved oxygen problems occurred during most
summer months.
Whiskey Creek – Whiskey Creek had relatively high nutrient loading but generally low
chlorophyll a concentrations in 2003-2004. There were a few incidents of low dissolved
oxygen at two of the five stations sampled this year, but high turbidity was not a
problem. Fecal coliform bacteria were not sampled in 2003-2004 in this creek.
Water Quality Station Ratings – The NC Division of Water Quality (NCDEHNR 1996)
utilizes an EPA-based system to help determine if a water body supports its designated
use (described in Appendix A). We applied these numerical standards to the water
bodies described in this report, based on 2003-2004 data, and have designated each
station as good, fair, and poor accordingly (Appendix B). Our analysis shows that (based on fecal coliform standards for human contact waters) the Barnards Creek
station was rated fair water quality. Two of the three stations in Burnt Mill Creek were
rated as poor in 2004, and the other was rated fair. The one Bradley Creek station
sampled for fecal coliforms was rated as poor. Futch Creek was rated as good for fecal
coliform bacteria, including for shellfishing in the lower creek. The Greenfield Lake tributaries were rated as poor microbiological water quality and the in-lake stations as
fair to good. The lower tidal stations in Hewletts Creek were rated good for fecal
coliforms; the middle stations as fair, and upper tidal stations as poor. The non-tidal
freshwater stations in the Hewletts Creek watershed were poor throughout. The
uppermost two stations in Howe Creek were rated poor and the lower three were rated good. Lower Motts Creek was rated poor, as was lower Smith Creek. We also list our
ratings for chlorophyll a, dissolved oxygen and turbidity in Appendix B.
Phytoplankton productivity in Futch and Hewletts Creeks - Phytoplankton are
microscopic plants found in marine, estuarine and freshwater ecosystems. Phytoplankton, like other plants, utilize sunlight to convert carbon dioxide into high-
energy carbohydrates and release oxygen during the process of photosynthesis. The
rate at which these processes take place is known as primary production. Collectively,
phytoplankton are the foundation of food webs in water systems, providing a nutritional
base for zooplankton and commercially important shellfish and finfish. Phytoplankton production in these tidal creeks is greatest in summer and lowest in winter, showing that
light and temperature control the basic seasonal patterns. Productivity is higher at low tide than high tide, and higher upstream than downstream. Also, productivity was
higher in Hewletts Creek than Futch Creek, demonstrating that the greater nutrient
inputs from the more highly developed watershed cause higher phytoplankton
productivity rates.
Our experiments also demonstrate that phytoplankton production in Futch and Hewletts
Creeks is high, equal to or greater than that of large eutrophic estuaries such as the
Neuse and Pamlico River Estuaries. However, these tidal creeks have not suffered
from the major algal bloom problems, toxic blooms, and fish kills that those larger
systems have had. Phytoplankton biomass and productivity can be greatly reduced due to grazing by zooplankton, shellfish and other predators. We suspect that intense
grazing by invertebrates such as oysters have helped to control excessive growth of
algae in these creeks, especially in summer months when phytoplankton production is
highest. This tells us that these creeks are habitats where there is intense food chain
activity, supporting the larval and juvenile stages of many species of finfish and shellfish, a major reason why these creeks are considered primary nursery areas for
marine life.
Fecal coliform contamination of sediments - Sediments in the Bradley Creek drainage
frequently harbored high numbers of potentially-pathogenic microbes including fecal coliform, streptococcus, and enterococcus bacteria, particularly during the warmer
times of the year when children are most likely to play in these waters. As other studies
have shown, fecal indicator bacteria concentrations in sediments correlate with the
presence of other fecal pathogens. 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. Human contact with these contaminated
sediments must be considered as a serious problem for heavily developed coastal
areas, such as the Bradley Creek watershed.
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 animal-derived pathogens, such as infectious protozoans, can cause infections that are difficult to diagnose and treat.
Tidal Creek Benthic Fauna - Settlement and survivorship of oyster spat are the two
most important factors determining the development and stability of oyster reefs within
any system. When reefs are constructed of shell hash with low relief high numbers of spat settle on them, because predators like crabs will avoid these open areas to avoid
getting eaten by larger fish. As reefs grow and their architecture becomes more
complex, many other species inhabit them and a complex food web develops. The habitat function of oyster reefs is critical especially in shallow estuarine environments
where oysters may represent one of the few structural habitats available. As oyster
reefs develop the number of crevices and the amount of internal space within the oyster
matrix increases. These areas are colonized very quickly by small crabs and shrimp
that may in turn prey on newly settled oyster spat. Thus as oyster reefs begin to provide a more complex refuge the overall survivorship of oyster spat may decline on
that reef to a stable level. This provides an excellent example of biological controls and
illustrates how a healthy ecosystem operates. As the oyster reefs develop they provide
more habitat allowing a greater number of species of epifauna (such as crabs and
shrimp), these species in turn provide food for many of the commercially and recreationally important finfish, such as drum, blue fish, spots and croaker among
others.
Thus, if rapid recolonization of an area by oysters is desired, construction of low reefs
of shell hash is likely to provide a boost in oyster colonization and reef expansion. If the additional benefit of increased habitat for the whole creek community is desired, reefs
of mixed complexity show a great deal of potential for the development of oyster reef for
habitat restoration and mitigation.
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 16
7.0 Hewletts Creek 20
8.0 Howe Creek 26 9.0 Motts Creek 30
10.0 Pages Creek 33
11.0 Smith Creek 35
12.0 Whiskey Creek 38
13.0 Phytoplankton Productivity in Futch and Hewletts Creeks 41 14.0 Fecal Contamination of Tidal Creek Sediments 48
15.0 Benthic Fauna of New Hanover County Tidal Creeks 56
16.0 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 Based on DWQ Chemical
Standards 67
20.0 Appendix C: GPS coordinates for the New Hanover County Tidal Creek
and Wilmington Watersheds Program sampling stations 69
21.0 Appendix D: UNCW reports and papers related to tidal creeks 71
(Cover by Heather Wells)
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 creek
watersheds analyzed in our program.
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. Also, certain
sites were analyzed for sediment heavy metals concentrations (EPA Priority Pollutants).
In the past six years we have produced combined Tidal Creeks – Wilmington City
Watersheds reports (Mallin et al. 1998b; 1999; 2000a; 2002a; 2003; 2004). In the present report we present results of continuing studies from August 2003 - July 2004 in
the tidal creek complex and January - September 2004 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 (TKN), total nitrogen (TN), total phosphorus (TP), suspended solids and biochemical oxygen demand (BOD)
at selected sites.
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. The UNCW Aquatic Ecology laboratory is State-Certified for
field measurements (temperature, conductivity, dissolved oxygen and pH).
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 Bran-Luebbe 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 18-24 hours. The solution containing the extracted chlorophyll 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 on seven occasions within the Wilmington City
watersheds from January through September 2004. Field measurements were taken
as indicated above. Nutrients (nitrate, ammonium, total Kjeldahl nitrogen, total nitrogen, orthophosphate, and total phosphorus) 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 a large wet detention pond (Ann McCrary Pond on Burnt Mill Creek) we
collected 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 Barnards and Motts Creeks. In 2004 we collected data at a station located on Barnards Creek at River Road (BNC-RR) that
drains part of this area (Fig. 2.1). Sampling at two other sites, BNC-CB site near
Carolina Beach Road and BNC-TR at Titanium Rd. has been discontinued.
BNC-RR had average salinity of 5.7 ppt with a range of 0.1-21.4 ppt. This station had dissolved oxygen levels below 5 mg/L (but above 4.0 mg/L) from May
through September. Concentrations of nutrients (total nitrogen, ammonium, and total
phosphorus) were among the highest in the Wilmington area (Table 2.1). Turbidity on
average was relatively high (21 NTU), and exceeded the state standard for estuarine
waters of 25 NTU three times out of the seven sampling periods. Total suspended solids concentrations were the highest among area creeks, particularly May through
July, but there were no algal bloom problems (Table 2.1). BOD5 was sampled seven
times at BNC-RR last year, yielding a median of 1.1 and a mean of 1.3 mg/L, which was
down from the BOD5 concentrations found in previous years (Mallin et al. 2003; 2004).
Median and mean BOD20 in 2004 was 5.5 and 5.9 mg/L, respectively, a slight decrease from the previous year. Fecal coliform counts exceeded the state standard
on only one of seven occasions for a 14% non-compliance rate, an improvement over
the previous two years. Thus, this station can be considered impaired by turbidity and
low dissolved oxygen, with comparatively high nutrient concentrations as well.
Table 2.1. Mean and standard deviation of water quality parameters in Barnards Creek watershed, January - September 2004. Fecal coliforms as geometric mean; N/P ratio as
median (n = 7 for all parameters).
_____________________________________________________________________
Parameter BNC-RR
_____________________________________________________________________
DO (mg/L) 6.1 (3.0)
Turbidity (NTU) 21 (8)
TSS (mg/L) 24.7 (8.5)
Nitrate (mg/L) 0.140 (0.138) Ammon. (mg/L) 0.247 (0.187)
TN (mg/L) 1.464 (0.374)
Phosphate (mg/L) 0.042 (0.043)
TP (mg/L) 0.127 (0.047)
N/P molar ratio 29.9
Chlor. a (µg/L) 3.5 (3.1)
BOD5 1.3 (0.6)
BOD20 5.9 (1.9)
Fec. col.(/100 mL) 121
_____________________________________________________________________
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 major problem during 2003-2004 (Table
3.1). The standard of 25 NTU was exceeded twice at the upper north branch
(November and December, 58 and 45 NTU, respectively) and once at the north branch (BC-NB) in December 2003 (37 NTU - Table 3.1). There were only minor problems
with low dissolved oxygen (hypoxia), with BC-76 having DO of less than 5.0 mg/L on
two occasions and BC-CA having substandard dissolved oxygen conditions on three of
seven sampling occasions (Appendix B).
Table 3.1 Water quality parameter concentrations at Bradley Creek sampling stations,
August 2003-July 2004. Data as mean (SD) / range, fecal coliform bacteria as
geometric mean / range; (for BC-CA, n = 7 months).
_____________________________________________________________________
Station Salinity Turbidity Dissolved Oxygen Fecal coliforms (ppt) (NTU) (mg/L) (CFU/100 mL)
_____________________________________________________________________
BC-76 30.1 (5.0) 5 (3) 7.5 (2.4) NA
18.6-36.4 0-13 4.5-11.3
BC-SB 8.0 (9.6) 7 (4) 8.0 (2.2) NA
0.1-27.3 3-18 3.6-11.1
BC-SBU 0.1 (0.0) 4 (5) 8.1 (1.8) NA 0.1-0.1 1-19 4.5-11.7
BC-NB 15.9 (13.0) 10 (9) 7.3 (2.1) NA
0.2-33.2 1-37 4.8-11.1
BC-NBU 0.1 (0.0) 15 (19) 7.7 (1.1) NA
0.1-0.2 1-58 6.4-9.5
BC-CR 0.1 (0.0) 3 (3) 7.9 (0.7) NA
0.1-0.1 0-8 6.5-9.1
BC-CA 0.1 (0.0) 7 (7) 6.4 (2.7) 807
0.1-0.2 1-22 4.3-11.4 60-6000
_____________________________________________________________________
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 six
of seven collections for an 86% exceedence rate (Table 3.1). We consider BC-CA 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 decreased slightly in the south branch in comparison to
the previous year. Ammonium was elevated at BC-CA, but 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 2003-2004, except for a minor bloom in June at BC-SB (24.3 µg/L) and a
major bloom (40.3 µg/L) in June at BC-CA (Table 3.2).
Table 3.2. Nutrient and chlorophyll a data at Bradley Creek sampling stations, August
2003-July 2004. Data as mean (SD) / range, nutrients in mg/L, chlorophyll a as µg/L.
_____________________________________________________________________
Station Nitrate Ammonium Orthophosphate Chlorophyll a _____________________________________________________________________
BC-76 0.015 (0.012) 0.023 (0.015) 0.012 (0.006) 1.2 (0.7)
0.003-0.042 0.008-0.049 0.005-0.023 0.3-2.2
BC-SB 0.070 (0.060) 0.024 (0.013) 0.013 (0.010) 5.1 (7.3) 0.003-0.169 0.008-0.041 0.005-0.044 0.6-24.7
BC-SBU 0.083 (0.033) NA 0.011 (0.011) 2.3 (3.1)
0.054-0.171 0.006-0.044 0.3-11.2 BC-NB 0.042 (0.051) 0.029 (0.022) 0.011 (0.008) 3.7 (3.6)
0.003-0.156 0.008-0.072 0.003-0.028 0.6-10.9
BC-NBU 0.087 (0.018) NA 0.005 (0.005) 0.5 (0.4) 0.062-0.123 0.002-0.020 0.1-1.2
BC-CR 0.274 (0.047) NA 0.007 (0.006) 0.4 (0.4)
0.154-0.317 0.002-0.024 0.1-1.5
BC-CA 0.085 (0.109) 0.121 (0.055) 0.019 (0.016) 11.2 (14.3) 0.013-0.330 0.040-0.190 0.005-0.040 1.5-40.3
_____________________________________________________________________
4.0 Burnt Mill Creek
The Burnt Mill Creek watershed was sampled just upstream of Ann McCrary
Pond on Randall Parkway (BMC-AP1), about 40 m downstream of the pond outfall
(BMC-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 BMC-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 entering and leaving the pond were low to moderate. Fecal coliform concentrations entering Ann McCrary Pond at BMC-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. All seven samples
collected in 2004 at BMC-AP1 had counts exceeding 200 CFU/100 mL; however, only
one sample at BMC-AP3 exceeded the standard. There were minor algal blooms at BMC-AP1 in May and June and in June at BMC-AP3 (with chlorophyll a concentrations
between 30 and 40 µg/L).
The efficiency of the pond as a pollutant removal device was poor last year.
Fecal coliforms were significantly reduced during passage through the pond (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. Neither ammonium,
nitrate, total nitrogen, orthophosphate nor total phosphorus 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 BMC-AP2 site (Fig. 4.1), short circuiting
the ability of the pond to remove nutrients. 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 (BMC-PP) experienced several water quality problems during the sample period (Appendix B). Dissolved oxygen was substandard (between 2.0 and 5.0 mg/L) from May through September 2004. The most
important issue, from a public health perspective, was the excessive fecal coliform
counts, which maintained a geometric mean (639 CFU/100 mL) well in excess of the
State standard for human contact waters (200 CFU/100 mL). Fecal coliform counts
were greater than 200 CFU/100 mL in five of seven months, or 71% of the time. It is notable that fecal coliform bacteria, ammonium, nitrate, TP and orthophosphate
concentrations all increased along the passage from BMC-AP3 to the Princess Place
location, while dissolved oxygen decreased (Table 4.1). No algal blooms exceeded the
State standard for chlorophyll a at Princess Place.
Table 4.1. Mean and (standard deviation) of water quality parameters in Burnt Mill
Creek, January - September 2004. Fecal coliforms as geometric mean; N/P as median.
_____________________________________________________________________
Parameter BMC-AP1 BMC-AP3 BMC-PP
_____________________________________________________________________ DO (mg/L) 6.5 (2.2) 9.5 (2.5)** 4.9 (2.3)
Cond. (µS/cm) 248 (39) 220 (61) 459 (389)
pH 6.8 (0.2) 7.5 (0.2)** 7.0 (0.2)
Turbidity (NTU) 5 (2) 8 (8) 5 (3) TSS (mg/L) 4.7 (2.4) 5.7 (3.7) 5.0 (2.5)
Nitrate (mg/L) 0.079 (0.060) 0.056 (0.040) 0.115 (0.086)
Ammonium (mg/L) 0.057 (0.035) 0.081 (0.102) 0.096 (0.075)
TN (mg/L) 0.787 (0.198) 1.164 (0.556) 1.126 (0.420)
OrthopPhosphate (mg/L) 0.012 (0.010) 0.007 (0.006) 0.021 (0.016) TP (mg/L) 0.066 (0.042) 0.053 (0.017) 0.080 (0.025)
N/P molar ratio 21.0 22.1 31.0
Fec. col. (/100 mL) 927 74** 639
Chlor. a (µg/L) 13.3 (14.6) 13.7 (13.3) 8.0 (11.9)
_____________________________________________________________________ * 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 2003-2004, there were
no incidences of creek stations having turbidity levels exceeding the state standard of
25 NTU (Table 5.1). Low dissolved oxygen, was a periodic problem at middle and
upper creek stations in 2003-2004 (Appendix B). Salinity levels were somewhat lower
in 2003-2004 than during the previous year (Table 5.1; Mallin et al. 2004); this may have been a result of more rainfall prior to this year's samples relative to last year's
collections.
Table 5.1. Physical parameters at Futch Creek sampling stations, August 2003 - July
2004. Data given as mean (SD) / range. _____________________________________________________________________
Station Salinity (ppt) Turbidity (NTU) Dissolved oxygen (mg/L)
_____________________________________________________________________
FC-4 33.2 (2.3) 6 (7) 7.6 (2.0) 27.3-35.6 0-25 4.8-11.1
FC-6 32.2 (2.7) 4 (3) 7.8 (2.1)
24.4-34.3 0-9 4.7-11.3
FC-8 29.3 (4.8) 7 (4) 7.4 (2.5)
18.5-32.6 1-13 4.0-11.6
FC-13 25.8 (2.7) 10 (7) 7.2 (2.6)
20.8-28.8 2-25 2.9-11.9
FC-17 16.5 (6.5) 10 (7) 6.8 (2.8)
5.4-24.4 3-25 2.3-12.2
FOY 25.3 (5.5) 7 (4) 6.9 (2.6) 11.4-31.0 1-12 4.0-12.2
_____________________________________________________________________
Nutrient concentrations in Futch Creek remained generally low, although
showing an increase in nitrate over the previous year in the upper stations FC-13 and FC-17 (Table 5.2). One source of nitrate has been identified as groundwater inputs
entering the marsh in springs existing in the area stretching from upstream of FC-17
downstream to FC-13 (Mallin et al. 1998b). The creek was free from algal blooms
during our sampling visits (Table 5.2), even in the upper stations.
Table 5.2. Nutrient and chlorophyll a data from Futch Creek, August 2003-July 2004.
Data as mean (SD) / range, nutrients in mg/L, chlorophyll a as µg/L.
_____________________________________________________________________
Station Nitrate Ammonium Orthophosphate Chlorophyll a
_____________________________________________________________________
FC-4 0.009 (0.004) 0.016 (0.006) 0.007 (0.003) 1.4 (0.9) 0.005-0.020 0.008-0.025 0.004-0.016 0.3-2.9
FC-6 0.012 (0.005) 0.016 (0.011) 0.008 (0.003) 1.4 (1.0)
0.004-0.020 0.008-0.035 0.004-0.016 0.3-3.3
FC-8 0.025 (0.011) NA 0.010 (0.004) 1.6 (1.1)
0.008-0.048 0.006-0.023 0.3-3.9
FC-13 0.062 (0.029) NA 0.011 (0.005) 3.0 (2.9)
0.027-0.115 0.006-0.023 0.5-10.1
FC-17 0.111 (0.064) 0.026 (0.016) 0.014 (0.008) 2.4 (1.6)
0.035-0.274 0.008-0.052 0.008-0.036 0.6-4.8
FOY 0.044 (0.029) 0.023 (0.010) 0.009 (0.005) 2.3 (1.8) 0.003-0.092 0.008-0.043 0.002-0.020 0.6-5.4
_____________________________________________________________________
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 2003-2004 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 below those of the pre-dredging period; however, there was a notable
deterioration in microbiological water quality at the upper stations compared with the previous year (Fig. 5.2). All stations still had geometric mean fecal coliform counts 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 2003 - July 2004. _____________________________________________________________________
Station FC-4 FC-6 FC-8 FC-13 FC-17 FOY
Geomean (CFU/100 mL) 2 3 8 19 77 24
% > 43 /100ml 0 10 10 20 70 50
_____________________________________________________________________
Figure 5.2 Fecal coliform bacteria counts over time at selected
Futch Creek stations, 1994-2004
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6.0 Greenfield Lake Water Quality
Three tributaries of Greenfield Lake were sampled for physical, chemical, and
biological parameters (Table 6.1, 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 periodically were 1.0 mg/L
or less at all three tributaries during the summer months (Table 6.1; Appendix B).
Turbidity and suspended solids were generally low in the tributary stations (Table 6.1).
total nitrogen and nitrate concentrations were highest at GL-LC, somewhat lower at GL-
LB, and lowest at GL-JRB (Table 6.1). Ammonium concentrations were highest at GL-LB, and generally similar across the other two tributary stations. Phosphorus
concentrations were similar at the three sites. 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) three
of seven times at GL-LB, five of seven times at GL-LC, and five of seven times at GL-JRB. There was one major algal bloom in June at GL-LC, with a chlorophyll a level of
95 µg/L.
Table 6.1. Mean and (standard deviation) of water quality parameters in tributary
stations of Greenfield Lake, January - September 2004. Fecal coliforms as geometric mean; N/P ratio as median; n = 7 samples for all parameters.
_____________________________________________________________________
Parameter GL-JRB GL-LB GL-LC
_____________________________________________________________________
DO (mg/L) 4.3 (3.3) 2.8 (2.1) 2.9 (1.8) Turbidity (NTU) 3 (1) 2 (1) 3 (3)
TSS (mg/L) 3.0 (1.6) 2.9 (1.3) 3.6 (3.1)
Nitrate (mg/L) 0.093 (0.065) 0.244 (0.180) 0.457 (0.418)
Ammonium (mg/L) 0.086 (0.046) 0.189 (0.075) 0.100 (0.031)
TN (mg/L) 1.106 (0.563) 1.509 (0.929) 1.546 (0.545) Orthophosphate (mg/L) 0.023 (0.017) 0.026 (0.014) 0.023 (0.013)
TP (mg/L) 0.070 (0.046) 0.097 (0.105) 0.074 (0.055)
N/P molar ratio 24.4 34.0 67.9
Fec. col. (/100 mL) 277 313 417
Chlor. a (µg/L) 4.1 (2.2) 1.8 (1.1) 15.6 (35.1)
_____________________________________________________________________
Three in-lake stations were sampled (Table 6.2). 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 all three sites (Appendix B), with GL-P suffering from DO < 1.0 mg/L from July
through September when the surface was covered by a dense bloom of duckweed
(Lemna sp.) mixed with various algae. Two major algal blooms occurred at GL-P and
one at GL-2340, and one minor bloom occurred at GL-YD. Turbidity and suspended solids were low to moderate at these three sites, with high TSS in September at GL-P.
In contrast to last year, fecal coliform concentrations were only problematic at GL-P (Appendix B) with three of seven samples exceeding the State standard in 2004.
Nitrate concentrations were similar among the three sites, while total nitrogen,
ammonium, and total phosphorus were highest at GL-P (Table 6.2). This was a result
of high summer ammonium and organic N near the park resulting from decaying bloom material. 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 6.2), phytoplankton growth in Greenfield Lake was close enough to the Redfield ratio that either nutrient could be
limiting at times. Our previous bioassay work indicated that nitrogen was usually the
limiting nutrient in this lake (Mallin et al. 1999).
Phytoplankton blooms are periodically problematic in Greenfield Lake, and usually consist of green or blue-green algal species, or both together. These blooms
have occurred during all seasons, but are primarily a problem in spring and summer.
As mentioned, three algal blooms exceeding the state standard of 40 µg/L were
recorded in our sampling during 2004, along with an intense surface scum of duckweed for three months. Thus, during 2004 Greenfield Lake was impaired by algal blooms,
high fecal coliform counts and low dissolved oxygen concentrations. The tributary
stations were also impaired by high fecal coliform counts and low dissolved oxygen.
These same problems have occurred in the lake for several years (Mallin et al. 1999;
2000; 2002; 2003; 2004).
Table 6.2. Mean and (standard deviation) of water quality parameters in Greenfield Lake sampling stations, January - September 2004. Fecal coliforms given as geometric
mean, N/P ratio as median; n = 7 samples collected.
_____________________________________________________________________
Parameter GL-2340 GL-YD GL-P
_____________________________________________________________________ DO (mg/L) 6.1 (1.7) 8.0 (3.9) 5.2 (5.0)
Turbidity (NTU) 2 (1) 2 (1) 6 (10)
TSS (mg/L) 4.6 (4.5) 6.3 (7.2) 22.4 (40.2)
Nitrate (mg/L) 0.109 (0.182) 0.060 (0.042) 0.101 (0.158)
Ammonium (mg/L) 0.024 (0.023) 0.044 (0.053) 0.134 (0.205) TN (mg/L) 1.053 (0.474) 1.426 (0.900) 1.919 (1.409)
OrthopPhosphate (mg/L) 0.009 (0.007) 0.010 (0.009) 0.018 (0.021)
TP (mg/L) 0.049 (0.046) 0.061 (0.036) 0.087 (0.079)
N/P molar ratio 22.1 22.1 22.1
Fec. col. (/100 mL) 61 28 153
Chlor. a (µg/L) 31.6 (56.6) 11.0 (7.8) 25.1 (25.6)
____________________________________________________________________
7.0 Hewletts Creek
Hewletts Creek was sampled at seven tidally-influenced areas (HC-M, HC-2, HC-
3, NWB, NB-GLR, MB-PGR and SB-PGR) and a freshwater runoff collection area
draining Pine Valley Country Club (PVGC-9 - Fig. 7.1). Four new freshwater stations in
the headwaters of the south branch (Fig. 7.2) were added this year. Physical data indicated that turbidity was well within State standards during this sampling period
(Tables 7.1 and 7.2). There were several incidents of hypoxia seen in our 2003-2004
sampling; three at NWB and three at SB-PGR (Appendix B). 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 were generally similar to 2002-2003. The chlorophyll a data
(Table 7.1) showed that Hewletts Creek hosted two major algal blooms at NB-GLR in
May and June (43.5 and 55.5 µg/L, respectively). Algal blooms have been common in
upper Hewletts Creek in the past (Mallin et al. 1998a; 1999; 2002a; 2004). Fecal
coliform bacterial counts showed a pattern of generally clean water in the lower creek, moderate pollution in mid-creek and the south branch at SB-PGR, and severe pollution
in the middle and north branches (MB-PGR and NB-GLR - Tables 7.1 and 7.2;
Appendix B).
Nitrate concentrations were elevated leaving the golf course at PVGC-9 relative to the other stations (Tables 7.1 and 7.2). Nitrate leaving the course decreased over the
previous year (2003) study (Mallin et al. 2004). Fecal coliform bacteria counts
exceeded State standards 86% of the time in 2004 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.
Figure 7.3 Fecal coliform bacterial counts over time at selected
Hewletts Creek stations.
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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
led to restoration work on one branch of a stream flowing through the course in hopes
of improving downstream water quality.
Table 7.1. Selected water quality parameters at lower and middle creek stations in
Hewletts Creek watershed as mean (standard deviation) / range, August 2003-July
2004.
_____________________________________________________________________ Parameter HC-M HC-2 HC-3 HC-NWB
_____________________________________________________________________
Salinity 32.7 (1.5) 32.8 (2.0) 29.5 (3.2) 19.5 (7.0)
(ppt) 30.3-34.5 28.7-34.6 24.5-34.4 10.5-30.1
Turbidity 4 (3) 4 (3) 6 (4) 10 (4)
(NTU) 0-8 0-9 1-13 3-15
DO 8.3 (1.6) 8.1 (1.8) 7.9 (1.9) 7.2 (2.5) (mg/L) 5.8-10.8 5.2-11.2 4.7-11.1 4.1-11.5
Nitrate 0.007 (0.004) 0.009 (0.007) 0.015 (0.012) 0.036 (0.028)
(mg/L) 0.003-0.017 0.003-0.024 0.004-0.043 0.003-0.078
Ammonium 0.015 (0.007) 0.012 (0.005) NA 0.027 (0.023)
(mg/L) 0.008-0.032 0.008-0.019 0.008-0.075
Orthophosphate 0.007 (0.007) 0.008 (0.005) 0.009 (0.005) 0.011 (0.007)
(mg/L) 0.002-0.014 0.003-0.018 0.004-0.017 0.002-0.024
Mean N/P 7.2 7.2 NA 12.0
Median 7.7 7.3 11.2
Chlor a 1.1 (0.9) 1.1 (0.6) 1.4 (1.0) 2.9 (2.5)
(µg/L) 0.1-3.0 0.2-2.0 0.3-3.6 0.3-6.6
Fecal col. 3 3 17 91
CFU/100 mL 3-74 3-184 2-283 26-1100
_____________________________________________________________________
The New Hanover County Tidal Creeks Advisory Board, using funds from the
North Carolina Clean Water Management Trust Fund, purchased a former industrial
area owned by the Dobo family in August 2002. This property is to be used as a passive treatment facility for the improvement of non-point source runoff drainage water
before it enters Hewletts Creek. As such, the City of Wilmington is contracting with
outside consultants to create a wetland on the property for this purpose. Baseline data were needed to assess water quality conditions before and after the planned
improvements. Thus, in January 2004 the UNCW Aquatic Ecology Laboratory began
sampling three inflowing creeks and the single outflowing creek (Fig. 7.2). DB-1 is a
creek/ditch entering the southern side of the property adjacent to Brookview Road. DB-
2 is a small stream entering the property along Bethel Road. DB-3 is a deeply-incised stream running along the northern edge of the property. DB-4 is the single outflowing
stream, sampled at Aster Court.
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 2003-July 2004; for PVGC-9, n = 7 months.
_____________________________________________________________________
Parameter NB-GLR SB-PGR MB-PGR PVGC-9
_____________________________________________________________________
Salinity 8.2 (7.6) 15.6 (7.0) 0.3 (0.6) 0.1 (0.0)
(ppt) 1.0-26.1 8.4-30.4 0.1-2.2 0.1-0.2
Turbidity 10 (7) 10 (6) 3 (2) 3 (2)
(NTU) 2-25 2-21 1-9 1-8
DO 7.5 (1.9) 7.1 (2.4) 7.7 (1.3) 6.6 (1.9)
(mg/L) 4.6-11.3 3.7-11.5 5.6-9.9 3.6-9.1
Nitrate 0.108 (0.040) 0.056 (0.039) 0.221 (0.077) 0.343 (0.159) (mg/L) 0.042-0.166 0.017-0.151 0.056-0.339 0.070-0.580
Ammonium 0.022 (0.009) 0.034 (0.028) 0.026 (0.009) 0.046 (0.020)
(mg/L) 0.008-0.039 0.009-0.095 0.008-0.039 0.020-0.080
Orthophosphate 0.021 (0.012) 0.012 (0.006) 0.015 (0.007) 0.007 (0.003)
(mg/L) 0.006-0.048 0.005-0.024 0.007-0.032 0.005-0.010
Mean N/P ratio 17.0 17.2 43.0 131.0
Median 17.6 16.6 35.3 137.3
Chlor a 12.2 (19.2) 4.0 (3.6) 1.1 (1.4) 1.7 (0.8)
(µg/L) 0.3-55.5 0.6-11.2 0.1-5.1 0.5-2.8
Fecal coliforms 292 136 171 363 CFU/100 mL 101-1725 43-415 49-1620 46-1900
_____________________________________________________________________
In 2004 all nutrient species had the highest concentrations at DB-1, while nitrogen concentrations were second highest at DB-2 and orthophosphate and TP
concentrations were second highest at DB-3 (Table 7.3). There was some reduction of
nutrients at DB-4, showing that the property already has some water quality improvement function. Dissolved oxygen was low only at DB-1, and turbidity and
suspended solids concentrations were low at all four sites. Fecal coliform bacteria
counts were consistently high at both DB-1 and DB-2, lower at DB-3, but high in the
outflowing stream DB-4 (Table 7.3). Thus, early data suggest that fecal coliform
bacteria and nutrient should be targeted for removal by the treatment facility.
Table 7.3. Selected water quality parameters at non-tidal Dobo site stations in Hewletts
Creek watershed, as mean (standard deviation) / range, fecal coliforms as geometric
mean / range, January - September 2004.
_____________________________________________________________________ Parameter DB-1 DB-2 DB-3 DB-4
_____________________________________________________________________
Turbidity 10 (12) 4 (1) 12 (5) 12 (3)
(NTU) 3-36 3-5 7-22 8-18
TSS 12.7 (12.1) 3.3 (0.8) 12.1 (8.3) 5.7 (1.3)
mg/L 2-33 2-4 5-25 5-8
DO 4.2 (2.2) 7.0 (1.7) 6.7 (1.6) 7.5 (1.6) (mg/L) 1.6-7.6 5.2-9.4 5.4-9.6 5.8-10.3
Nitrate 0.174 (0.196) 0.106 (0.099) 0.077 (0.073) 0.044 (0.010)
(mg/L) 0.020-0.590 0.030-0.320 0.030-0.230 0.030-0.060
Ammonium 0.321 (0.296) 0.091 (0.059) 0.227 (0.078) 0.191 (0.055)
(mg/L) 0.120-0.950 0.040-0.210 0.110-0.350 0.120-0.260
TN 1.533 (0.629) 1.200 (0.581) 1.174 (0.342) 1.154 (0.437)
(mg/L) 0.580-2.590 0.500-2.290 0.760-1.810 0.790-2.050
Orthophosphate 0.056 (0.049) 0.007 (0.006) 0.023 (0.017) 0.014 (0.012)
(mg/L) 0.005-0.150 0.005-0.020 0.005-0.050 0.005-0.030
TP 0.140 (0.050) 0.029 (0.016) 0.063 (0.029) 0.050 (0.020) (mg/L) 0.080-0.230 0.005-0.050 0.020-0.110 0.010-0.070
Chlor a 1.0 (1.2) 4.2 (3.4) 0.7 (0.9) 1.4 (1.1)
(µg/L) 0.2-3.6 0.7-10.0 0.1-2.8 0.3-3.6
Fecal coliforms 790 469 41 234
CFU/100 mL 80-3300 17-3000 1-2650 1-3000
_____________________________________________________________________
8.0 Howe Creek Water Quality
Howe Creek was sampled for physical parameters, nutrients, chlorophyll a , and
fecal coliform bacteria at five locations during 2003-2004 (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-GP below the standard of 5.0 mg/L on two occasions (Appendix B). Nutrient levels were
generally low except for nitrate at HW-DT (Table 8.2). Nitrate levels showed a slight
increase over levels in 2002-2003, especially at the uppermost stations (Mallin et al.
2004). Median inorganic molar N/P ratios were low, reflecting low nitrate levels, and,
indicating that nitrogen was probably the principal nutrient limiting phytoplankton growth
at all stations. There was one major algal bloom of 56 µg/L as chlorophyll a at HW-DT
and a minor bloom of 28 µg/L at HW-GP. Since wetland enhancement was performed
in 1998 above Graham Pond the creek below the pond at HW-GP has had fewer and
smaller algal blooms than before the enhancement (Fig. 8.2).
Table 8.1. Water quality summary statistics for Howe Creek, August 2003-July 2004,
as mean (st. dev.) / range.
Salinity Diss. oxygen Turbidity Chlor a Fecal coliforms
(ppt) (mg/L) (NTU) (µg/L) (CFU/100 mL) _____________________________________________________________________
HW-M 34.2 (1.9) 8.0 (1.8) 4 (3) 1.2 (0.9) 3
31.5-37.5 5.2-10.8 0-11 0.3-2.8 1-18
HW-FP 33.7 (2.1) 7.9 (2.0) 4 (3) 0.9 (0.6) 5 30.4-37.3 5.0-11.0 0-10 0.3-1.9 1-41
HW-GC 29.3 (4.5) 7.6 (2.3) 6 (3) 1.3 (0.8) 21
23.0-36.8 4.0-11.6 1-14 0.4-2.4 4-139 HW-GP 14.5 (11.9) 7.4 (2.3) 10 (4) 6.5 (8.0) 185
0.6-30.1 4.1-10.9 3-18 0.9-27.9 46-465
HW-DT 4.2 (6.1) 8.6 (2.2) 15 (8) 10.2 (17.0) 419 0.2-18.7 6.1-12.6 4-28 0.7-56.1 70-1810
Figure 8.2. Chlorophyll a concentrations in Howe Creek below Graham
Pond before and after 1998 wetland enhancement in upper Graham Pond.
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e
Ch
l
o
r
o
p
h
y
l
l
a
(
p
p
b
)
1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
NC chlorophyll a
standard
wetland
enhancement
Table 8.2. Nutrient concentration summary statistics for Howe Creek, August 2003-July
2004, as mean (st. dev.) / range, N/P ratio as mean / median.
_____________________________________________________________________
Nitrate Ammonium Orthophosphate Molar N/P ratio (mg/L) (mg/L) (mg/L)
_____________________________________________________________________
HW-M 0.005 (0.003) 0.014 (0.008) 0.007 (0.002) 6.0
0.003-0.016 0.008-0.031 0.005-0.011 5.2
HW-FP 0.007 (0.006) 0.013 (0.007) 0.008 (0.003) 5.4
0.003-0.022 0.008-0.029 0.006-0.015 4.3
HW-GC 0.008 (0.007) NA 0.010 (0.004) NA 0.003-0.026 0.006-0.019
HW-GP 0.022 (0.023) 0.019 (0.013) 0.011 (0.004) 8.2
0.003-0.067 0.008-0.045 0.006-0.021 6.8
HW-DT 0.047 (0.040) 0.023 (0.014) 0.012 (0.006) 14.7
0.003-0.106 0.008-0.055 0.006-0.029 18.7
____________________________________________________________________
Fecal coliform bacterial abundances were low near the Intracoastal Waterway,
moderate in mid-creek, and high in the uppermost stations (Table 8.1; Fig. 8.3). HW-
GP exceeded the North Carolina human contact standard on five of ten occasions, and
HW-DT exceeded the standard on seven of nine occasions (Appendix B). After
several years of improvement (i.e. lower fecal coliform counts in the upper two stations), in 2003-2004 Howe Creek experienced a degradation in bacteriological water quality
(Fig. 8.3). Both Station HW-GP and HW-DT experienced a doubling in geometric mean
fecal coliform counts compared with the period 2001-2003. This occurred in spite of the
moving of Masons Inlet across the waterway. The increase in coliform counts may be a
result of the continuing development occurring in the Howe Creek headwaters area along Military Cutoff. It has been demonstrated for New Hanover County (Mallin et
al.2000b) and the Charleston, S.C. area (Holland et al. 2004) that increases in human
development on land are strongly correlated statistically with increases in tidal creek
fecal coliform bacteria counts. This is particularly troublesome since Howe Creek is
considered an Outstanding Resources Water by the State of North Carolina.
Figure 8.3. Geometric mean fecal coliform bacteria counts for Howe
Creek over time
0
100
200
300
400
500
600
HW-M HW-FP HW-GC HW-GP HW-DT
STATION
Fe
c
a
l
c
o
l
.
b
a
c
t
e
r
i
a
(
C
F
U
/
1
0
0
m
L
)
1993-1994 1996-1997 1999-2000 2001-2002 2002-2003 2003-2004
N.C. fecal coliform standard for human
contact waters (200 CFU/100 mL)
9.0 Motts Creek
Motts 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 Motts
Creek at the River Road bridge (Fig. 9.1). A large residential development is scheduled
for construction upstream of the sampling site between Motts and Barnards Creeks. In
recent years extensive commercial development has occurred along Carolina Beach
Road near its junction with Highway 421.
Dissolved oxygen concentrations were below 5.0 mg/L from May through
September (range 3.6-4.9 mg/L) similar to previous years (Mallin et al. 2003; 2004).
Unlike previous years, neither turbidity nor suspended solids were problematic in 2004.
Fecal coliform contamination was a problem in Motts Creek, with the geometric mean of 272 CFU/100 mL exceeding the State standard of 200 CFU/100 mL, and samples
exceeding this standard on five of seven occasions (Appendix B). Fecal coliform
contamination was similar to previous years. Total nitrogen, ammonium, and total
phosphorus levels decreased over the previous year’s study, but chlorophyll a
concentrations generally increased, with one major and one minor bloom (Table 9.1). BOD5 was sampled on seven occasions in 2004, yielding a mean value of 1.7 mg/L
and a median value of 1.2 mg/L, which was lower than the previous years (Mallin et al.
2003; 2004). Thus, this creek showed mixed water quality, with algal blooms increasing
but BOD and turbidity decreasing, and dissolved oxygen and fecal coliform counts
staying relatively similar to last year. Cessation of the commercial development activities near the headwaters upstream may have contributed to the decrease in BOD
and nutrient loading 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)
and range, January-September 2004. Fecal coliforms as geometric mean / range.
_____________________________________________________________________
Parameter MOT-RR
Mean (SD) Range _____________________________________________________________________
Salinity (ppt) 2.8 (4.6) 0.1-21.3
TSS (mg/L) 9.7 (4.6) 5.0-19.0
Turbidity (NTU) 13 (6) 8-25
DO (mg/L) 5.3 (2.4) 3.6-10.0
Nitrate (mg/L) 0.110 (0.119) 0.030-0.350
Ammonium (mg/L) 0.041 (0.018) 0.005-0.060
Total nitrogen (mg/L) 1.103 (0.170) 0.780-1.290
Orthophosphate (mg/L) 0.014 (0.010) 0.005-0.030
Total phosphorus (mg/L) 0.060 (0.015) 0.040-0.080
Mean N/P ratio 32.3
Median 24.4
Chlor a (µg/L) 11.3 (15.5) 1.8-41.1
BOD5 (mg/L) 1.7 (1.1) 0.8-3.7
BOD20 5.9 (3.3) 1.8-11.5
Fecal coliforms (CFU/100 mL) 272 90-900
_____________________________________________________________________
10.0 Pages Creek
Pages Creek was sampled at three stations, two of which receive drainage from
developed areas near Bayshore Drive (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 2003 and 2004, two each at the stations draining Bayshore Drive
(Appendix B). Fecal coliform bacteria were not sampled at this creek during the past
year. Nitrate and orthophosphate concentrations showed a notable increase over the
previous year, although phytoplankton biomass as chlorophyll a was low with no algal
blooms noted (Table 10.1). Median inorganic nitrogen-to-phosphorus molar ratios were
well 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 Pages Creek as mean (standard deviation) / range, August 2003-July 2004.
_____________________________________________________________________
Parameter PC-M PC-BDDS PC-BDUS
_____________________________________________________________________
Salinity (ppt) 34.4 (2.2) 30.2 (7.1) 16.5 (11.4)
30.2-38.4 11.0-36.3 1.2-34.1
Turbidity (NTU) 5 (3) 6 (4) 9 (6)
1-9 1-14 3-23
DO (mg/L) 7.6 (2.0) 7.3 (2.3) 7.4 (2.0)
5.2-10.6 4.1-10.6 4.5-10.6
Nitrate (mg/L) 0.008(0.003) 0.036(0.035) 0.035(0.024) 0.004-0.017 0.004-0.108 0.004-0.074
Ammonium (mg/L) 0.016(0.007) 0.032(0.029) 0.046(0.020)
0.008-0.034 0.008-0.106 0.008-0.068
Orthophosphate (mg/L) 0.008(0.003) 0.013(0.007) 0.019(0.010)
0.005-0.015 0.006-0.026 0.005-0.038
Mean N/P Ratio 6.9 11.7 10.7
median 6.6 9.5 9.2
Chlor a (µg/L) 1.4 (0.7) 3.6 (3.3) 4.2 (4.0)
0.3-2.4 0.5-9.4 0.8-13.5
_____________________________________________________________________
11.0 Smith Creek
Two estuarine sites on Smith Creek proper, SC-23 and SC-CH (Fig. 11.1) are
normally sampled; however, SC-23 was not sampled in 2004 due to construction
activities. Discussion of Smith Creek is thus limited to the SC-CH station on the bridge
at Castle Hayne Rd. Dissolved oxygen concentrations were below 5.0 mg/L on four occasions between May and September 2004. 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 two of seven occasions at
SC-CH, similar to last year. Suspended solids concentrations in Smith Creek were
second only to Barnards Creek in the Wilmington watersheds system.
Nutrient concentrations remained similar to last year's levels (Table 11.1), and
algal blooms exceeding the State standard were not found in 2004, similar to the
previous year (Mallin et al. 2004). Fecal coliform bacteria concentrations were above
200 CFU/100 mL on two of seven occasions at SC-CH, approximately the same as last year (Mallin et al. 2004) and all months tested well above the shellfishing standard (14
CFU/100 mL) in the estuarine portion of the creek (Table 11.1). BOD5 was sampled on
seven occasions in 2004 at SC-CH, with a mean value of 1.5 mg/L and a median value
of 1.3 mg/L, a very slight decrease over last year.
Table 11.1. Selected water quality parameters in Smith Creek watershed as mean (standard deviation) / range. January - September 2004.
_____________________________________________________________________
Parameter SC-CH
Mean (SD) Range
_____________________________________________________________________
Salinity (ppt) 2.3 (3.6) 0.0-15.7
Dissolved oxygen (mg/L) 5.9 (2.9) 3.1-11.4
Turbidity (NTU) 19 (10) 8-38
TSS (mg/L) 20.1 (8.6) 11.0-37.0
Nitrate (mg/L) 0.117 (0.133) 0.040-0.380
Ammonium (mg/L) 0.096 (0.068) 0.040-0.240
Total nitrogen (mg/L) 1.443 (0.348) 1.070-2.010
Orthophosphate (mg/L) 0.025 (0.022) 0.005-0.060
Total phosphorus (mg/L) 0.101 (0.070) 0.070-0.150
Mean N/P ratio 32.0 Median 31.0
Chlor. a (µg/L) 4.5 (4.1) 0.7-9.0
Fecal col. /100 mL 104 27-673 (geomean / range)
BOD5 (mg/L) 1.5 (1.2) 0.8-4.1
BOD20 (mg/L) 5.7 (3.4) 1.8-12.9
_____________________________________________________________________
12.0 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. 12.1). Dissolved oxygen
concentrations were below the State standard on two of 12 occasions at WC-MLR and
WC-NB in 2003-2004 (Table 12.1). Turbidity was within state standards for tidal waters
on all sampling occasions except for November 2003 at WC-SB (Table 12.1; Appendix B). There were no algal blooms during this period; chlorophyll a concentrations were
usually low (Table 12.1). Nitrate concentrations were highest upstream at WC-NB,
followed by WC-SB (Table 12.2), similar to previous years. Ammonium levels were
highest at WC-NB and WC-SB, and these levels were among the highest of all 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 were not sampled in 2003-2004. Whiskey Creek is presently closed to
shellfishing by the N.C. Division of Marine Fisheries.
Table 12.1. Water quality summary statistics for Whiskey Creek, August 2003-July 2004, as mean (st. dev.) / range.
Salinity Dissolved oxygen Turbidity Chlor a
(ppt) (mg/L) (NTU) (µg/L)
_____________________________________________________________________
WC-MB 29.7 (3.5) 7.8 (2.0) 5 (3) 2.0 (1.2) 20.6-35.0 5.3-11.0 1-13 0.6-4.8
WC-AB 27.3 (4.1) 7.9 (2.2) 7 (5) 1.6 (1.1)
17.1-33.1 5.4-11.1 1-18 0.5-3.9 WC-MLR 24.1 (5.8) 7.7 (2.4) 9 (7) 2.3 (2.2)
12.5-32.6 4.4-11.4 1-24 0.5-6.5
WC-SB 0.1 (0.0) 7.7 (1.2) 14 (29) 0.4 (0.2) 0.0-0.2 6.4-10.1 3-104 0.1-0.9
WC-NB 0.2 (0.0) 6.8 (2.1) 6 (3) 0.3 (0.2)
0.1-0.2 3.6-10.2 3-12 0.1-0.8
Table 12.2. Nutrient concentration summary statistics for Whiskey Creek, August 2003-July 2004, 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 0.025 (0.023) 0.028 (0.022) 0.011 (0.005) 10.3
0.006-0.086 0.008-0.082 0.007-0.022 9.9
WC-AB 0.034 (0.030) NA 0.015 (0.007) NA 0.004-0.100 0.007-0.028
WC-MLR 0.036 (0.028) 0.043 (0.035) 0.014 (0.008) 18.1
0.004-0.095 0.008-0.113 0.002-0.030 9.3
WC-SB 0.063 (0.037) 0.101 (0.020) 0.003 (0.001) 149.7
0.023-0.165 0.070-0.132 0.002-0.005 153.3
WC-NB 0.196 (0.062) 0.113 (0.071) 0.007 (0.004) 114.3
0.081-0.284 0.060-0.317 0.003-0.016 101.3 _____________________________________________________________________
13.0 Phytoplankton Productivity in Futch and Hewletts Creek
by
Virginia L Johnson Center for Marine Science
University of North Carolina at Wilmington
Wilmington, NC
Introduction
Phytoplankton are microscopic plants found in marine, estuarine and freshwater
ecosystems. Phytoplankton, like other plants, utilize sunlight to convert carbon dioxide into high-energy carbohydrates and release oxygen during the process of
photosynthesis. The rate at which these processes take place is known as primary
production. Collectively, phytoplankton are the foundation of food webs in water
systems, providing a nutritional base for zooplankton and other commercially important
shellfish and finfish.
Typically, marine, estuarine and freshwater phytoplankton abundance is
dependent on a number of physical environmental factors including, but not limited to,
light, temperature, salinity and some function of nutrient availability. Phytoplankton
productivity and abundance has been shown to correspond to seasonal fluctuations in water temperature and day length throughout many east coast estuaries (Dame et al.
2000, Caffrey 2004, Mallin 1994). Nitrogen, phosphorus, and iron, among other
nutrients, have been shown to limit algal growth in freshwater, coastal and open ocean
systems (Ryther and Dunstan 1971). The biological characteristics of the system also
play a role in regulating primary productivity, as phytoplankton abundance can be a function of zooplankton grazing (Mallin and Paerl 1994).
Tidal creek ecosystems are widespread and highly abundant along the Atlantic
Seaboard and Gulf Coast. Unlike many larger neighboring estuaries, tidal creeks
systems do not necessarily follow a longitudinal river-ocean continuum and generally have a higher surface area to volume ratio than river-dominated estuaries. Collectively,
this could make their importance in material transfer and other ecological processes on
par or even greater than larger estuaries in some regions (Mallin and Lewitus 2004).
Unfortunately, tidal creek ecosystems are enduring changes as a result of a steadily increasing human population along the Atlantic Coast, including southeastern
North Carolina. Urbanization results in disturbances such as land clearing, application
of fertilizers, discharge of human and animal waste and increased impervious surface
coverage, which collectively act to increase nitrogen and phosphorus concentrations in
neighboring surface waters and ground waters. Nutrient over-enrichment, or eutrophication, can have profound effects on ecosystem processes by over-stimulating
phytoplankton productivity and biomass accumulation leading to nuisance and toxic
algal blooms (Cloern 2001). Eutrophication is also often associated with increased
biochemical oxygen demand and subsequent low dissolved oxygen problems (Mallin et al. in press), reductions in available light energy for benthic plants and changes in the
plant community (Cloern 2001). This can lead to changes in the natural function of tidal
creeks as fish and wildlife habitat. Trends show overall decreases in algal species
diversity in streams with increasing urban land use usually due to factors including
water chemistry (Paul and Meyer 2001).
Estuarine systems have a hydrological link to terrestrial landscapes and are thus
subject to non-point source (NPS) runoff from the upland watershed. While locations
near the mouth of an estuary would be expected to be more closely characteristic of the
coastal ocean, headwaters can receive an influx of materials from the upland
watershed. Chemical pollutants including nutrients, pesticides, and heavy metals bind to sediments from the terrestrial landscape and are introduced into water systems via
NPS runoff. In an urban landscape nutrient molecules have been shown to travel
further distances downstream before removal from the water column, suggesting that
normal nutrient removal efficiency can be greatly reduced (Paul and Meyer 2001).
Urban streams have displayed a greater tendency to suffer from low dissolved oxygen when compared to forested streams primarily attributed to increases in labile sources of
carbon, or BOD, from the upland watershed (Paul and Meyer 2001).
Two tidal creeks in southeastern North Carolina, Futch Creek and Hewletts
Creek, will be principal subjects of the current study. Both creeks receive anthropogenic nutrient loading, especially in upstream areas, and have been host to
occasional algal blooms. Mallin et al. (1999) conducted an earlier study of Hewletts
Creek and Futch Creek and discovered that the phytoplankton community within these
systems is very distinct. During high tide in Futch Creek, the community was very
diverse and increased phytoplankton abundance was attributed to a greater number of tiny pennate diatoms. More flagellates characterized low tide in Futch Creek. Hewletts
Creek phytoplankton abundances were more than an order of magnitude higher at low
tide than high tide and the community was dominated by flagellates and cryptomonads
(Mallin et al. 1999).
The purpose of this study was to determine how season, tide, location within the
creek and watershed development impacts phytoplankton productivity in local tidal
creeks.
Methods
Three sites were studied in both Futch Creek (FC-4, FC-6, FC-17, Fig 5.1) and
Hewletts Creek (HC-2, SB-PGR, NB-GLR, Fig. 7.1). Field sampling was conducted
monthly at high ebb tide from October 2003 thru September 2004. Beginning in March
2004 sampling was conducted monthly at both high ebb and low flood tide.
Vertical profiles of field parameters included water temperature, pH, dissolved
oxygen, turbidity, salinity, and specific conductivity. Light attenuation was collected in
situ using vertical profiles collected with a Li-Cor LI-193S spherical quantum sensor.
Total daily irradiance was logged at the UNCW Center for Marine Science, New
Hanover County, NC, (Figure 2) during the week of sampling using a Li-Cor pyranometer.
Rates of primary productivity by phytoplankton were measured using the rate of
incorporation of radioactive carbon (14C). All samples were inoculated with 0.5 ml of
4µCi NaH14CO3. Dark treatments were inoculated with 1.0 ml DCMU (3-(3,4-
dichlorophenyl)-1,1 dimethylurea), a photosynthetic electron transfer inhibitor, to
account for nonphotosynthetic uptake of 14C. Duplicate light and single dark samples
were incubated in situ in a Plexiglas bottle suspension rack for 3 to 4 hours, centered
on local noon. After incubation, all samples were filtered individually and filters were
placed into separate glass vials containing 10 mL of scintillation cocktail. Samples were radioassayed by liquid scintillation counting. Total primary productivity was determined
from the equations of Wetzel and Likens (2000).
Phytoplankton biomass was determined via chlorophyll a pigment analysis, a
fluorometric technique (Welshmeyer 1994). Phytoplankton samples were collected during spring and summer at low and high tide and field preserved with Lugol’s iodine.
Nitrate and orthophosphate were analyzed using a Technicon AutoAnalyzer III
following EPA protocols. Ammonium was analyzed according to the methods of
Parsons et al. (1984). Dissolved inorganic carbon (DIC) was analyzed using a Shimadzu TOC-5050A total organic carbon analyzer.
Results
Mean annual production in Hewletts Creek was approximately 521 gC m-3 and 257 gC m-3 in Futch Creek. Temporally, productivity was significantly higher during late spring and summer months than during winter months (Fig. 1). Peak productivity
corresponded with the summer chlorophyll a maximum (Fig. 2). There was high spatial
variability between sites in Hewletts Creek, however, productivity was only significantly
higher in the north branch of Hewletts Creek during summer months when compared to
downstream reaches. There was no significant spatial variability between sites in Futch Creek. The site with the highest mean daily productivity at high tide was site NB-GLR
(1,348 mgC m-3 day-1). The site with the lowest mean daily productivity at high tide was
site HC-2 (216 mgC m-3 day-1). Productivity was higher at low tide in both creek
systems. There was a decrease in high tide productivity directly following Hurricane
Charley in August of 2004, which was most likely a result of decreased water column light caused by high turbidity directly following Hurricane Charley (Fig. 1).
Phytoplankton biomass, as chlorophyll a, was significantly higher in Hewletts
Creek (5.8µg l-1) than Futch Creek (1.7µg l-1) (Fig. 2). The highest mean chlorophyll a
concentration at high tide occurred at site NB-GLR where algal blooms (>25µg l-1 of chl a) occurred in May and June of 2004. Algal blooms were present at site SB-PGR at low
tide during the months of April, May and June of 2004. Phytoplankton biomass was
significantly higher during summer months than during winter months. Spatially,
biomass in the upper reaches of Hewletts Creek was significantly higher than the
downstream portions. There was no significant spatial variation in chlorophyll a
biomass in Futch Creek. Mean chlorophyll a concentrations were significantly higher at
low tide when compared to high tide in both creeks.
Peak dissolved oxygen concentrations were present during the winter months
and began to decline during spring. There were no incidents of hypoxia (<2mg l-1) in
surface or bottom waters at high tide during the sampling year; however, there was one
incidence of hypoxia at site SB-PGR at low tide in August 2004 (1.3 mg l-1). It should be noted that in addition to Hurricane Charley, a spill of over 100,000 gallons of raw
sewage occurred in Hewletts Creek at site SB-PGR in the month of August 2004.
General trends indicate increased nutrient concentrations in the upstream
portions of both creeks. Nutrient concentrations were elevated in Hewletts Creek, especially at site SB-PGR, during the sewage spill in August 2004. Mean ammonia
concentrations were higher in Hewletts Creek (64.4 µg l-1) than Futch Creek (27.3 µg l-
1). The ammonia concentration during the sewage spill at site SB-PGR at high tide
sampling was 1303 µg l-1 and the concentration at low tide was 1,418µg l-1. Low tide
ammonia concentrations were higher than high tide at all stations sampled. Similar to
ammonia, nitrate-nitrite concentrations were higher in Hewletts Creek (68.1 µg l-1) than
Futch Creek (49.7µg l-1) at high tide. Elevated nitrate was present in Hewletts Creek at
site SB-PGR (135.0 µg l-1) during the sewage spill in August 2004. Nitrate
concentrations at low tide were generally higher than high tide. Orthophosphate
concentrations were also higher at high tide in Hewletts Creek (23.3 µg l-1) than Futch
Creek (16.9µg l-1) and higher at low tide compared to high tide. Peak orthophosphate
concentrations in Hewletts Creek occurred during August 2004.
Figure 1. Mean monthly primary productivity versus temperature at high tide in
Hewletts Creek (HC) and Futch Creek (FC), October 2003 – September 2004.
0
50
100
150
200
250
300
350
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Pr
i
m
a
r
y
P
r
o
d
u
c
t
i
v
i
t
y
(m
g
C
/
m
3/h
r
)
0.0
5.0
10.0
15.0
20.0
25.0
30.0
Te
m
p
e
r
a
t
u
r
e
(
OC)
HC Production FC Production Temperature
Hurricane Charley
Figure 2. Mean monthly primary productivity versus chlorophyll a at high tide in
Hewletts Creek (HC) and Futch Creek (FC), October 2003 – September 2004.
0.0
50.0100.0
150.0
200.0
250.0300.0
350.0
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Pr
i
m
a
r
y
P
r
o
d
u
c
t
i
v
i
t
y
(m
g
C
/
m
3/h
r
)
0.0
5.0
10.0
15.0
20.0
25.0
Ch
l
o
r
o
p
h
y
l
l
a
(
u
g
/
L
)
HC Prod FC Prod HC Chla FC Chla
Hurricane Charley
Discussion
Preliminary data suggest that the characteristic physical environmental forces
(temperature and light) govern basic seasonal, temporal and tidal patterns in
phytoplankton production. However, greater anthropogenic nutrient loading did lead to greater phytoplankton productivity in Hewletts Creek, the more developed watershed.
Major weather events, such as Hurricane Charley can have a pronounced effect on key
ecosystem processes, in this case depressing phytoplankton productivity in summer,
when productivity would usually be elevated.
Table 1. Annual primary production by phytoplankton for Hewletts Creek and Futch
Creek as compared to rates in other coastal NC systems (Mallin 1994). _____________________________________________________________________
Beaufort Estuaries 56 gC m-3
Neuse River Estuary 75 gC m-3
Futch Creek 91 gC m-3
South River 144 gC m-3 Pamlico River Estuary 150 gC m-3
Hewletts Creek 246 gC m-3
_________________________________________________________________________________________________________
_______
A comparative analysis of annual primary production by phytoplankton in Futch
Creek and Hewletts Creek with other neighboring North Carolina estuaries suggests
that these systems could play an important role in coastal ecological processing (Table
1). However, these creeks have not suffered from major algal bloom problems. Phytoplankton biomass and productivity can be greatly reduced due to grazing by
zooplankton, shellfish and other predators. Models of bivalve filtration rates in shallow
waters predict that sufficient numbers of bivalves can control phytoplankton biomass. A
study of bivalve populations in Hewletts Creek demonstrated 10-25% decreases in
chlorophyll a concentrations as water flowed over oyster reefs, especially in summer
months when phytoplankton biomass was high (Cressman et al. 2003). While consumption rates on phytoplankton were not studied in this project it is important to
note that grazing by oysters and other predators could have a significant effect on primary production by phytoplankton in local tidal creeks.
Literature Cited
Caffrey, J.M. 2004. Factors controlling net ecosystem metabolism in U.S.
estuaries. Estuaries. 27(1): 90-101.
Cloern, J.E. 2001. Our evolving conceptual model of the coastal eutrophication
problem. Marine Ecology Progress Series. 210: 223-253.
Cressman, K.A., Posey, M.P., Mallin, M.A., Leonard, L.A. and Alphin, T.D. 2003.
Effects of oyster reefs on water quality in a tidal creek estuary. Journal of Shellfish
Research. 22(3): 753-762.
Dame, R., Alber. M., Allen, D., Mallin, M., Montague, C., Lewitus, A., Chalmers, A., Gardner, R., Gilman, G., Kjerfve, B., Pinckney, J. and Smith, N. 2000.Estuaries of the south Atlantic Coast of North America: Their geographical signatures. Estuaries.
23(6): 793-819.
Mallin, M.A. 1994. Phytoplankton ecology of North Carolina estuaries. Estuaries.
17(3): 561-574.
Mallin, M.A. and Paerl, H.W. 1994. Planktonic trophic transfer in an estuary:
seasonal, diel and community structure effects. Ecology. 75(8): 2168-
2184.
Mallin, M.A., Esham, C.A., Williams, K.E. and Nearhoof, J.E. 1999. Tidal stage variability of fecal coliform and chlorophyll a concentrations in coastal
creeks. Marine Pollution Bulletin. 38(5): 414-422.
Mallin, M.A. and Lewitus, A.J. 2004. The importance of tidal creek ecosystems.
Journal of Experimental Marine Biology and Ecology. 298: 145-149.
Mallin, M.A., V.L. Johnson, S.H. Ensign and T.A. MacPherson. (in press) Factors contributing to hypoxia in rivers, lakes and streams. Limnology and Oceanography.
Paul, M. and Meyer, J. 2001. Streams in the urban landscape. Annual Review of
Ecology and Systematics. 32: 333-365.
Parsons, T.R., Maita, V., and Lalli, C.M. 1984. A Manual of Chemical and
Biological Methods for Seawater Analysis. Pergamon Press, Oxford.
Ryther, J.H., and W.M. Dunstan. 1971. Nitrogen, phosphorus, and
eutrophication in the coastal marine environment. Science. 171: 1108-
1013.
Welshmeyer, N.A. 1994. Fluorometric analysis of chlorophyll a in the presence
of chlorophyll b and phaeopigments. Limnology and Oceanography. 39:
1985-1993.
Wetzel, R.G., and Likens, G.E. 2000. Limnological Analysis. Springer-Verlag,
New York. 429pp.
14.0 Fecal contamination of tidal creek sediments – relationships to sediment phosphorus and among indicator bacteria
Lawrence B. Cahoon, Byron R. Toothman, Michelle L. Ortwine, Renee N. Harrington,
Rebecca S. Gerhart, Shannon L. Alexander, and Tara D. Blackburn
Dept. of Biological Sciences
UNC Wilmington
910-962-3706, Cahoon@uncwil.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 earlier
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.
Ongoing 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 body contact 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 (Jan. 1 2003 to December 1, 2004. Line at concentration = 200 denotes NC standard for human contact.
_____________________________________________________________________
We have 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, and now we have
funding from UNC Sea Grant to attack the question: Do sediment phosphorus levels
show any correlation with sediment fecal coliform levels? In addition we are measuring
the concentrations of other fecal contamination indicators (fecal streptococci and fecal
enterococci) and comparing these values with other parameters.
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, streptococci, and
enterococci, 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 indicator bacteria 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 sterile phosphate-buffered rinse water inside
a sterile 1L
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.
_____________________________________________________________________
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.
Similar methods were used to estimate fecal streptococci and fecal enterococci
following method 9230 C (APHA, 1998).
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 137
samples (sites x times) collected between January, 2003 and December, 2004. The
arithmetic mean value observed was 349 CFU cm-2 overall, which corresponds to a
value of 349 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; 110 of the 137 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 (“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 523 44 441 328 301 436 Range 2.5-4047 0-343 20.3-3475 0-3271 7.6-3070 0-6859
There was no significant correlation (r=0.02, df = 1,122) 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. Relationship between sediment fecal coliform concentrations and sediment P
concentrations, Jan. 1, 2003 – November 11, 2004.
The concentrations of fecal coliforms and other indicator bacteria in sediments
showed that, although there appears to be some relationship between these indicators, fecal coliform concentrations alone may actually underestimate the potential risk to
human health from exposure to contaminated sediments (Fig. 4a, b). Concentrations of
fecal enterococci more often exceeded comparable standards than did fecal coliform
concentrations, for example. This difference is congruent with regulatory agencies’ use
of the enterococcus standard in salt waters, owing to the relatively poorer survival of fecal coliform bacteria in salt water.
Collectively, these data strengthen the argument that estuarine sediments harbor
significant populations of fecal contaminants, including pathogens. Additional data and
analysis will be required to evaluate interactions of the factors considered above in controlling the concentrations of sediment fecal indicator bacteria. It is also likely that
other parameters, such as availability of organic substrates, are important.
Discussion
Sediments in the Bradley Creek drainage frequently harbored significant
populations of fecal coliform, streptococcus, and enterococcus bacteria, particularly
during the warmer times of year when children are most likely to play in these waters.
As other studies have shown that fecal indicator bacteria concentrations in sediments
correlate with 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.
Fig. 4a. Regression of fecal enterococci vs. fecal coliforms in sediments of the Bradley Creek drainage, June – November, 2004. Lines within graph denote limits for human
body contact if all observed bacteria were suspended in 1 m of water (fecal coliforms:
200 CFU/100ml; fecal enterococcus: 33 CFU/100 ml). Relationship is significant;
r=0.25, F=8.84, df=1,25, p=0.0064.
Fig. 4b. Regression of fecal streptococcus vs. fecal coliforms in sediments of the
Bradley Creek drainage, June – November, 2004. Relationship is significant; r=0.19,
F=4.97, df=1,24,p=0.0354.
Human contact with these contaminated sediments must be considered as a serious problem for heavily developed coastal areas, such as the Bradley Creek
drainage.
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 studies, which provided the data
in Fig. 1, 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 began in May, 2004, and includes efforts to examine a much larger
suite of parameters related to fecal contamination 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 BENTHIC FAUNA OF NEW HANOVER COUNTY TIDAL CREEKS
Troy Alphin and Martin Posey
UNCW Benthic Ecology Laboratory
Introduction
Over the last decade the UNCW Benthic Ecology Lab has evaluated the tidal
creek estuaries in the New Hanover County with a multi-disciplinary approach,
considering benthic faunal communities (the critical link between primary production and the health of fisheries in the tidal creeks), primary production (an evaluation of the
energy available to the first order consumers), ambient nutrient levels (a measure of
natural and anthropogenic inputs), and select water quality parameters. This work,
supported mainly from North Carolina Sea Grant and the New Hanover Tidal Creeks
Program, has shown the importance of predation (Posey et. al. 1999) in structuring benthic communities and the importance of scaling (Posey et. al. 2002) in determining
nutrient impacts in the tidal creeks systems of New Hanover County. These tidal creek
systems are dynamic, meaning that the factors that influence the system (and its
function) change in relative importance based on seasonal factors and event-driven
watershed impacts. For example the amount of nutrients that run into the watershed varies among years with the change in the amount of impervious surface within the
watershed, but also on shorter time scales with interactive effects between rain events
and ongoing development, having a large impact on the system (at least for some
parameters). For this reason it is imperative that we begin to understand the function of
organisms such as oysters that are considered ecosystem engineers and have been proposed as effective modifiers of ecosystem function.
Oyster Reefs as Modifiers of Water Quality
Since 2001 the Benthic Ecology lab has focused on the function of oyster populations in the tidal creeks. Specifically, we have studied the potential interactions
between oyster reefs and water quality and the influence oyster reef morphology has on
the utilization of oyster reefs and on the development of the reefs themselves. General
surveys of oyster reefs in the tidal creek show that they cover roughly one-third of the
intertidal area within the lower sections of each tidal creek. However, this is somewhat misleading because much of the reef surface is actually dead shell and live oyster
density varies greatly within and among the creeks (Mallin et. al. 2004). As part of a
collaborative project with the UNCW Aquatic Ecology Lab and the UNCW Coastal
Hydrology and Sedimentology Lab, we conducted several studies in 2002 specifically
evaluating the water quality impacts that live oyster populations can have on the small-scale fringing tributaries of the tidal creeks. These fringing creeks tend to be small (1-
2m deep at high tide and 3-4m wide) but represent the actual source of much of the
run-off from communities within the watershed. This work showed that relatively small
additions of live oyster (12 sq m) could reduce levels of total suspended solids and
chlorophyll downstream of the oyster patches (Nelson et. al. 2004). Another study focused on the effect of naturally formed oyster reefs within the main stem of the
Hewletts Creek system. This study specifically tested the upstream/downstream impact
of live oyster filtration, it also tested the idea that varying live oyster density may
influence oyster impacts on water quality. Specific findings indicate that during summer
periods oysters can significantly (and consistently) reduce chlorophyll levels by 10-25% and that they can have similar effects on fecal coliforms in the spring, although the
amount removed was much more variable. Moreover, rough modeling indicated that
the chlorophyll reduction was not solely due to filtration but may also be affected by hydrodynamic changes related to reef structure (shell) - in other words the structure
may enhance settling of particles in and near the reef. Overall this work indicated that
both feeding of live oysters and the influence of oyster structure work to reduce levels
of chlorophyll and bacteria in the water column (Cressman et. al. 2003).
Oyster Reefs as Habitat
Oysters serve a variety of functions within the estuarine ecosystem. Clearly they
act as modifiers of water quality, but they also provide critical refuge for a number of
organisms, including commercially important finfish such as those targeted by recreational anglers. Based on the previously mentioned work, Sea Grant has
supported a new study to evaluate the influence that oyster reef morphology has on the
various ecosystem functions that oysters play - such as water quality impacts and
habitat for finfish and crustaceans. While the impact that oysters have on water quality
is significant and critical to understanding their ecosystem impacts, it has become clear that we must also understand the factors that influence oyster reef utilization and reef
development from a habitat perspective. This study has evaluated utilization of oyster
reefs based on reef edge (convoluted vs. circular) and vertical complexity. In this case
low vertical complexity was represented by a reef constructed of flat unarticulated shell,
with only a couple of centimeters of relief, and high vertical complexity was simulated by reefs with both patches of flat shell and by patches of oyster matrix. A third treatment
evaluated small fragmented reefs of high vertical complexity that represent reefs as
they begin to experience fragmentation. (Fragmentation is the process where habitat
patches become degraded and large patches are reduced to several small patches).
All of these reef types were compared for utilization by finfish and crustaceans as well as for aspects of reefs development such as settlement and survivorship of oysters.
This work indicated interesting patterns related to aspects of oyster reefs
development. Total oyster spat settlement and initial survivorship was greater on oyster
reefs made of shell hash that had lower vertical complexity compared to reefs of higher vertical complexity, fragmented reefs or natural reef controls regardless of the edge
treatment (circular vs convoluted) (Figure 1) (Posey et. al., in prep.). A possible
mechanism for these differences may be that greater abundances of predatory crabs
live in high-relief reef systems. As the reefs developed, the initially low vertical
complexity treatments became identical to the high vertical complexity treatment in year two. These finding have significant implications for future restoration projects and for
resource managers that are tasked with enhancing the harvestable oyster populations.
0
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Figure 1. Mean spat settlement by treatment (live, dead, and shell
scars represent total settlement. circ= circular edge,
con=convoluted edge, low=low complexity,high=high complexity)
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In 2002 and 2003 we evaluated oyster populations within the various tidal creeks
of New Hanover County based on the coverage of oyster reefs and the density of live
oyster populations within the various reefs, as well as categorize the reefs by the
amount of vertical relief seen in the various creeks. These studies illustrated the general difference among the various creeks, with Hewletts and Pages creeks
consistently showing higher values for live oyster density and coverage (Mallin et. al.
2004).
Given the demonstrated differences in oyster characteristics among the creeks, in 2004 the focus shifted to evaluating the oyster spat settlement and subsequent
survivorship based on high and low vertical complexity within the natural reefs of each
creek. The objective in this study was to determine if the oysters that settled in natural
reefs demonstrated similar settlement and survivorship, based on relative complexity as
seen in the previous study of oyster reefs. Creek differences in reef complexity indicate broad-scale implications for any complexity effects.
Methods
Oyster settlement bags were placed within areas of high and low vertical complexity within Hewletts, Bradley, Howe, and Pages Creeks and in a clam lease area
at the mouth of Hewlettes Creek. Each bag contained 10 unarticulated shells. All shell
used in the settlement experiments was clean shell that had been dried for at least 6
months. Within each creek three sites representing low vertical complexity and three
areas representing high vertical complexity were sampled. It should be noted here that based on previous findings, the low vertical complexity treatments in the natural reefs
within each creek had a greater amount of surface rugosity (complexity) than the low
vertical complexity treatments previously described in the reef morphology study (Mallin
et. al. 2004). Settlement bags were placed in the oyster reefs representing each
treatment in April and retrieved in July and a second set was deployed in July and retrieved October. All live oysters, scars, and recently dead oysters were counted. All
three of these measurements allow us to calculate the total number of oysters that settled within each creek.
Results
Overall total settlement was an order of magnitude lower in the tidal creeks in 2004 then was previously seen in the Sea Grant study. We believe this represented
interannual variability rather than differences among locations because settlement was
lower in all plots monitored, even those outside the creek environments. No significant
differences were detected between high and low relief treatments in any of the tidal
creeks (Figure 2), though there was a trend towards higher recruitment within low complexity plots in Hewletts Creek (consistent with previous Sea Grant work at the
mouth of that creek). There was also no detectable difference for total abundances of
oyster spat between natural high and low relief areas (within the same reef) when data
from all creeks is combined (Figure 3). Evaluation of survivorship does show some very
different patterns with twice as many initial survivors in Pages and Hewletts creeks compared to Howe and Whiskey creeks (Figure 4).
0
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Figure 2. Mean abundance of oyster spat settlement by
creek
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Figure 3. Total abundance of oyster spat for all creeks
combined
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Figure 4. Percent survivorship by creek
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Conclusions
Settlement and survivorship are the two most important factors determining the
development and stability of oyster reefs within any system. Findings of initially high settlement and survivorship of oyster spat on low reefs constructed solely of shell hash
compared to reefs constructed with a greater degree of vertical complexity show a great
deal of potential for the development of oyster reef for habitat restoration and
mitigation. Low reefs lead to initial rapid colonization, while more complex reefs lead to
less oyster colonization but better habitat for the entire community. The comparison presented here between areas within natural reefs with high and low vertical complexity
suggests that differences in habitat type may be due in part or whole to the habitat
provided by oysters to other organisms. The habitat function of oyster reefs is critical
especially in shallow estuarine environments where oysters may represent one of the few structural habitats available (Larsen 1985, Breitberg 1999, Posey et. al. 1999, Coen
et. al. 1999). As oyster reefs develop the number of crevices and the amount of
internal space within the oyster matrix increases. These areas are colonized very
quickly by small crabs and shrimp that may in turn prey on newly settled oyster spat.
Thus as oyster reefs begin to provide a more complex refuge the overall survivorship of oyster spat may decline. This provides an excellent example of biological controls and
illustrates how a healthy ecosystem operates. As the oyster reefs develop they provide
more habitat allowing a greater number of species of epifauna including crabs and
shrimp, these species in turn provide food for many of the commercially and
recreationally important finfish, such as drum, blue fish, spots, croaker among others.
Current Projects
The UNCW Benthic Ecology Laboratory currently has two projects focused on
evaluating the factors that influence the development of oyster reefs within the New Hanover County tidal creeks. 1) One project evaluates the role that early colonizing
xanthid crabs play in survivorship of oysters and other reef resident fauna. 2) The
second project involves the detection of disease and disease burden in oyster
population based on factors of reef complexity. These two projects will evaluate how
intertidal oyster reefs develop, with a goal of providing the resource managers and restoration groups with information that will increase their effectiveness as replacing
and enhancing the oyster population.
Citations
Breitburg, D.L. 1999. Are three-dimensional structure and healthy oyster populations
keys to an ecologically interesting and important fish community? P.239-250. In:
M.W. Luckenback, R. Mann, and J.A. Wesson (eds.), Oyster reef habitat restoration:
a synopsis and synthesis of approaches. Virginia Institute of Marine Science Press.
Coen, L.D., M.W. Luckenbach, and D.L. Breitburg. 1999. The role of oyster reefs as
essential fish habitat: a review of current knowledge and some new perspectives.
American Fisheries Society Symposium, Vol. 22. 438-454.
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. Vol. 22 (3):53-762.
Larsen, P.F. 1985. The benthic macrofauna associated with the oyster reefs of the
James River estuary, U.S.A. Int. Rev. Gesamt. Hyddrobiol. 70:797-814.
Mallin, M.A., L.B. Cahoon, M.H. Posey, V.L. Johnson, T.D. Alphin, D.C. Parsons, and
J.F. Merritt. 2004. Environmental quality of Wilmington and New Hanover County
watersheds 2002-2003. CMS Report 04-01.
Nelson, K.A., L.A. Leonard, M.H. Posey, T.D. Alphin, and M.A. Mallin. 2004. Using
transplanted oysters (Crassostrea virginica) beds to improve water quality in small
tidal creeks: a pilot study. Journal of Experimental marine biology and Ecology 298: 347-368.
Posey, M.H., T.D. Alphin, L. Cahoon, D. Lindquist and M.E. Becker. 1999. Interactive
effects of nutrient additions and predation on benthic communities. Estuaries 22:
785-792.
Posey, M.H., T.D. Alphin, L.B. Cahoon, D.G. Lindquist, M.A. Mallin and M.B. Nevers.
2002. Top-down versus bottom-up limitation in benthic communities: direct and
indirect effects. Estuaries. 25: 999-1014.
16.0 Report References Cited
APHA. 1995. Standard Methods for the Examination of Water and Wastewater, 19th
ed. American Public Health Association, Washington, D.C.
Hecky, R.E. and P. Kilham. 1988. Nutrient limitation of phytoplankton in freshwater and marine environments: A review of recent evidence on the effects of enrichment.
Limnology and Oceanography 33:796-822.
Holland, A.F., D.M. Sanger, C.P. Gawle, S.B. Lerberg, M.S. Santiago, G.H.M. Riekerk,
L.E. Zimmerman and G.I. Scott. 2004. Linkages between tidal creek ecosystems and the landscape and demographic attributes of their watersheds. Journal of
Experimental Marine Biology and Ecology 298:151-178.
Mallin, M.A., L.B. Cahoon, J.J. Manock, J.F. Merritt, M.H. Posey, R.K. Sizemore, W.D.
Webster and T.D. Alphin. 1998a. A Four-Year Environmental Analysis of New
Hanover County Tidal Creeks, 1993-1997. CMSR Report No. 98-01, Center for
Marine Science Research, University of North Carolina at Wilmington, Wilmington, N.C. Mallin, M.A., L.B. Cahoon, J.J. Manock, J.F. Merritt, M.H. Posey, T.D. Alphin, D.C.
Parsons and T.L. Wheeler. 1998b. Environmental Quality of Wilmington and New
Hanover County Watersheds, 1997-1998. CMSR Report 98-03. Center for Marine
Science Research, University of North Carolina at Wilmington, Wilmington, N.C.
Mallin, M.A., S.H. Ensign, D.C. Parsons and J.F. Merritt. 1999. Environmental Quality of
Wilmington and New Hanover County Watersheds, 1998-1999. CMSR Report No.
99-02. Center for Marine Science Research, University of North Carolina at
Wilmington, Wilmington, N.C.
Mallin, M.A. and T.L. Wheeler. 2000. Nutrient and fecal coliform discharge from coastal
North Carolina golf courses. Journal of Environmental Quality 29:979-986.
Mallin, M.A., S.H. Ensign, D.C. Parsons, V.L. Johnson and J.F. Merritt. 2000a.
Environmental Quality of Wilmington and New Hanover County Watersheds, 1999-
2000. CMSR Report No. 00-02. Center for Marine Science, University of North
Carolina at Wilmington, Wilmington, N.C.
Mallin, M.A., K.E. Williams, E.C. Esham and R.P. Lowe. 2000b. Effect of human
development on bacteriological water quality in coastal watersheds. Ecological
Applications 10:1047-1056.
Mallin, M.A., L.B. Cahoon, R.P. Lowe, J.F. Merritt, R.K. Sizemore and K.E. Williams. 2000c. Restoration of shellfishing waters in a tidal creek following limited dredging.
Journal of Coastal Research 16:40-47.
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. 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., L.B. Cahoon, M.H. Posey, V.L. Johnson, T.D. Alphin, D.C. Parsons and J.F. Merritt. 2004. Environmental Quality of Wilmington and New Hanover County Watersheds, 2002-2003. CMS Report 04-01, Center for Marine Science, University of North Carolina at Wilmington, Wilmington, N.C.
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Report No. 96-03. North Carolina Department of Environment, Health, and Natural Resources, Division of Water Quality. Raleigh, N.C.
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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 Heather
Wells, Matt McIver, Jonathan Hartsell, Maverick Raber, Jen O'Reilly, 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 tidal creek watersheds based on August 2003 – July 2004 data for tidal creeks
and January -September 2004 data for 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-RR G P P F Bradley Creek BC-CA G G G P
BC-CR G G G -
BC-SB G G G -
BC-SBU G G G - BC-NB G G G - BC-NBU G G F -
BC-76 G F G -
Burnt Mill Creek BMC-AP1 G F G P BMC-AP3 G G G F BMC-PP G P G P
Futch Creek FC-4 G G G G
FC-6 G G G G FC-8 G F G G FC-13 G F G G
FC-17 G F G G
FOY G G G F
Greenfield Lake GL-LC F P G P GL-JRB G P G P
GL-LB G P G P
GL-2340 F F G F
GL-YD G F G G GL-P P F G P
Hewletts Creek HC-M G G G G HC-2 G G G G
HC-3 G G G G
HC-NWB G P G F
NB-GLR F G G P
MB-PGR G G G P SB-PGR G F G F
PVGC-9 G G G P
DB-1 G P G P
DB-2 G G G P
DB-3 G G G P DB-4 G G G P
Howe Creek HW-M G G G G
HW-FP G G G G
HW-GC G G G G HW-GP G F G P
HW-DT G G G P
Motts Creek MOT-RR F P G 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
Whiskey Creek WC-NB G G G -
WC-SB G G G -
WC-MLR G F G -
WC-AB G G G - WC-MB G F 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 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
PVGC-9 N 34.19165 W 77.89175
DB-1 N 34.1764 W 77.8775
DB-2 N 34.1781 W 77.8805
DB-3 N 34.1799 W 77.8798 DB-4 N 34.1789 W 77.8752
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.
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., 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.
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., L.B. Cahoon, M.H. Posey, V.L. Johnson, T.D. Alphin, D.C. Parsons and J.F. Merritt. 2004. Environmental Quality of Wilmington and New Hanover County Watersheds, 2002-2003. CMS Report 04-01, Center for Marine Science, University
of North Carolina at Wilmington, Wilmington, N.C.
Mallin, M.A., H.A. Wells and M.R. McIver. 2004. Baseline Report on Bald Head Creek
Water Quality. CMS Report No. 04-03, Center for Marine Science, University of
North Carolina at Wilmington, Wilmington, N.C.
Mallin, M.A., H.A. Wells, T.A. MacPherson, T.D. Alphin, M.H. Posey and R.T. Barbour.
2004. Environmental Assessment of Surface Waters in the Town of Carolina Beach.
CMS Report No. 04-02, Center for Marine Science, University of North Carolina at
Wilmington, Wilmington, N.C.
Peer-Reviewed Journal Papers
Mallin, M.A., E.C. Esham, K.E. Williams and J.E. Nearhoof. 1999. Tidal stage variability
of fecal coliform and chlorophyll a concentrations in coastal creeks. Marine Pollution
Bulletin 38:414-422.
Mallin, M.A. and T.L. Wheeler. 2000. Nutrient and fecal coliform discharge from coastal North Carolina golf courses. Journal of Environmental Quality 29:979-986.
Mallin, M.A., K.E. Williams, E.C. Esham and R.P. Lowe. 2000. Effect of human
development on bacteriological water quality in coastal watersheds. Ecological
Applications 10:1047-1056.
Mallin, M.A., L.B. Cahoon, R.P. Lowe, J.F. Merritt, R.K. Sizemore and K.E. Williams. 2000. Restoration of shellfishing waters in a tidal creek following limited dredging.
Journal of Coastal Research 16:40-47.
Mallin, M.A., J.M. Burkholder, L.B. Cahoon and M.H. Posey. 2000. The North and
South Carolina coasts. Marine Pollution Bulletin 41:56-75.
Mallin, M.A., S.H. Ensign, M.R. McIver, G.C. Shank and P.K. Fowler. 2001. Demographic, landscape, and meteorological factors controlling the microbial
pollution of coastal waters. Hydrobiologia 460:185-193.
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.