ENVIRONMENTAL QUALITY OF WILMINGTON AND
NEW HANOVER COUNTY WATERSHEDS
2004-2005
by
Michael A. Mallin, Lawrence B. Cahoon, Martin H. Posey, Virginia L. Johnson,
Douglas C. Parsons, Troy D. Alphin, Byron R. Toothman, Michelle L. Ortwine
and James F. Merritt
CMS Report 06-01
Center for Marine Science
University of North Carolina Wilmington
Wilmington, N.C. 28409
www.uncw.edu/cmsr/aquaticecology/tidalcreeks
March 2006
Funded by:
The City of Wilmington, New Hanover County and the North Carolina Clean Water
Management Trust Fund
1
Executive Summary
This report represents combined results of Year 11 of the New Hanover County Tidal
Creeks Project and Year 7 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 54 sampling stations. In this summary
we first present brief water quality overviews for each watershed from data collected
between August 2004 – September 2005, and then discuss key results of several
special studies conducted over the past two years.
Barnards Creek – Barnards Creek drains into the Cape Fear River Estuary. There was
only one station sampled in this watershed during 2005, lower Barnard’s Creek at River
Road. This site had no algal bloom, BOD or turbidity problems; but it had poor water
quality in terms of fecal coliform counts and low dissolved oxygen. It also had among
the highest suspended solids, ammonium, total nitrogen and total phosphorus levels
among all the local watersheds.
Bradley Creek – Bradley Creek drains the largest tidal creek watershed in the area,
including much of the UNCW campus, into the Atlantic Intracoastal Waterway (ICW).
Seven sites are sampled, all from shore. Turbidity was not problematic during 20042005. 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,
and one minor and one major algal bloom occurred in the creek in the south branch
(BC-SB) at Wrightsville Avenue. Fecal coliform bacterial samples were only collected
at BC-CA, where contamination was excessive during six of the seven samples
collected in 2005.
Burnt Mill Creek – Burnt Mill Creek drains an extensive urban area into Smith Creek.
The number of sampling stations on Burnt Mill Creek was increased from three to six in
2005, because of additional funding from the EPA319 program through North Carolina
State University. There were no turbidity or suspended solids problems in 2005, but the
creek showed poor water quality in terms of substandard dissolved oxygen, with four
out six stations having dissolved oxygen concentrations below the State standard >
25% of the time sampled. High fecal coliform counts were a problem, with five out of
six sites exceeding the human contact standard > 25% of occasions sampled. There
were also some algal bloom problems at Anne McCrary Pond on Randall Parkway and
at the Princess Place station. The effectiveness of Ann McCrary wet detention pond as
a pollution control device was poor during 2005. 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
Wallace Park and Princess Place sampling stations. The constructed wetland on Kerr
Avenue led to a significant decrease in ammonium, but none of the other nutrient
species. Fecal coliform bacteria counts did not decrease through that pond in 2005,
nor did BOD. Sampling of the sediments for potential toxicants showed some problems
2
with elevated lead concentrations, and problems with excessive concentrations of
polycyclic aromatic hydrocarbons (PAHs) at all sites tested.
Futch Creek – Futch Creek is situated on the New Hanover-Pender County line and
drains into the ICW. Six locations are sampled by boat. Futch Creek maintained good
microbiological water quality, as it has since channel dredging at the mouth occurred in
1995 and 1996. Algal blooms, turbidity, and low dissolved oxygen were not problems in
2004-2005. This creek continues to display some of the best water quality in the New
Hanover County tidal creek system, due to generally low development and impervious
surface coverage in its watershed.
Greenfield Lake – This urban lake is sampled at three in-lake sites and at three tributary
sites. 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. 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. There were some algal bloom problems at the Jumping Run
Branch site.
In spring 2005 several steps were taken by the City of Wilmington to restore viability to
the lake. During February, 1,000 sterile grass carp were introduced to the lake to
control (by grazing) the overabundant aquatic macrophytes. During that same month
four SolarBee water circulation systems were installed in the lake to improve circulation
and force dissolved oxygen from the surface downward toward the bottom. Finally,
from April through June a contract firm applied the herbicide Sonar to further reduce the
amount of aquatic macrophytes. These actions led to a major reduction in aquatic
macrophytes lake wide. However, six algal blooms exceeding the state standard of 40
µg/L were recorded among the three in-lake sampling stations during July-September
2005 (an increase over the previous year). Despite the blooms, there was also an
improvement in dissolved oxygen concentrations over the previous two years, possibly
through the use of the SolarBees. Fecal coliform bacteria pollution was a problem in
the main lake, particularly at the park station. Thus, during 2005 Greenfield Lake was
impaired by algal blooms, high fecal coliform counts and low dissolved oxygen
concentrations, although there was definite improvement in dissolved oxygen
concentrations compared with the previous two years. Whereas in 2004 average
summer surface dissolved oxygen concentrations ranged from 2.9-6.8 mg/L, in summer
2005 average surface dissolved oxygen concentrations ranged from 8.2-9.9 mg/L.
Hewletts Creek – Hewletts Creek drains a large watershed into the ICW, which is
sampled by boat at four sites and from shore at eight sites. Hewletts Creek was
impacted by two sewage spills during summer 2005. Nutrient loading from one of these
spills (in July) caused two major algal blooms in the north branch (NB-GLR) and the
south branch (SB-PGR) plus a minor bloom at SB-PGR. There were several incidents
of hypoxia seen in our regular monthly 2004-2005 sampling; two at NB-GLR, three at
NWB and four at SB-PGR, and several additional incidents of hypoxia following the July
sewage spill. The hypoxia from the spill also caused a large fish kill on the creek during
the July 4th weekend, and subsequent mortality of some ducks. Fecal coliform counts
were low to moderate at the lower and mid-creek sites, and high in terms of the N.C.
3
human contact standard of 200 CFU/100 mL at the north and middle branches, but
moderate at the south branch. The sewage spills led to high July and September water
column fecal coliform counts, and prolonged occurrences (over two months) of high
fecal bacteria counts in the sediments of the upper branches.
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, turbidity, or algal bloom problems, and relatively high nitrate
levels. Fecal coliform bacteria counts exceeded State standards 86% of the time in
2005 at PVGC-9, an increase over last year. 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. In 2005 all nutrient species had
the highest concentrations at DB-1 and lowest at DB-2. There was some reduction of
nutrients at DB-4 compared with DB-1, showing that the property already has some
water quality improvement function. The exception was nitrate, which had similar
concentrations at DB-1 and DB-4. Dissolved oxygen was low only at DB-1, and
turbidity was low at all four sites. Suspended solids concentrations were periodically
elevated at DB-1, but low at the other three sites. Fecal coliform bacteria counts were a
problem at all four sites, and were highest at DB-1 followed by DB-4 and DB-2. The
data suggest that fecal coliform bacteria and nitrogen should be targeted in particular
for removal by the treatment facility.
Howe Creek – Howe Creek drains into the ICW. Five stations were sampled in Howe
Creek in 2004-2005. Turbidity did not exceed North Carolina water quality standards at
any of the stations. Dissolved oxygen concentrations were generally good in Howe
Creek, with HW-GP below the standard of 5.0 mg/L on two occasions. Nutrient levels
were generally low except for nitrate at HW-DT. Nitrate levels showed a decrease over
levels in 2003-2004, especially at the uppermost stations, probably a reflection of lower
rainfall and runoff. There was one minor algal bloom of 38 µg/L as chlorophyll a at HWDT. 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. Fecal coliform bacterial abundances were low near the Intracoastal
Waterway, moderate in mid-creek, and high in the uppermost station, with HW-DT
exceeding the State standard on seven of 12 occasions. The 2004-2005 data show an
improvement in fecal coliform counts after a sharp decrease in bacterial water quality
seen in 2003-2004. Less urban runoff as a result of the drought of 2005 may be
responsible for the lowered counts.
Motts Creek – Motts Creek drains into the Cape Fear River Estuary. This creek was
sampled at only one station, at River Road. Dissolved oxygen concentrations were
below 4.5 mg/L from May through September 2005 (range 2.8-4.4 mg/L) similar to
previous years. Unlike previous years, neither turbidity nor suspended solids were
problematic in 2005, possibly a result of low rainfall. Fecal coliform contamination was
a problem in Motts Creek, with the geometric mean of 353 CFU/100 mL exceeding the
State standard of 200 CFU/100 mL, and samples exceeding this standard on six of
seven occasions. Fecal coliform contamination increased over that of previous years.
Nutrient levels were similar to the previous year’s study, but chlorophyll a
4
concentrations generally decreased, with no algal blooms detected in 2005. BOD5
samples yielded a mean value of 1.3 mg/L and a median value of 1.2 mg/L, generally
lower than the previous years. Thus, this creek showed mixed water quality, with algal
blooms and BOD decreasing, and dissolved oxygen and fecal coliform counts
somewhat poorer compared with last year.
Pages Creek – Pages Creek drains into the ICW. This creek was sampled at three
stations, two of which receive drainage from developed areas near Bayshore Drive (PCBDUS and PC-BDDS). During the past sample year turbidity was low with no incidents
of turbidity exceeding the state standard of 25 NTU. However, there were three
incidents of hypoxia during summers of 2004 and 2005, all at the station draining upper
Bayshore Drive. Fecal coliform bacteria were not sampled at this creek during the past
year. Nitrate and orthophosphate concentrations were similar to the previous year, and
phytoplankton biomass as chlorophyll a was low with only one minor algal bloom of 23
µg/L noted at PC-BDUS. Because of the relatively low watershed development and low
amount of impervious surface coverage in the watershed, this is one of the leastpolluted creeks in New Hanover County.
Smith Creek – Smith Creek drains into the lower Northeast Cape Fear River just
upstream of where it merges with the Cape Fear River. Two estuarine sites on Smith
Creek proper, SC-23 and SC-CH were sampled in 2005. Dissolved oxygen
concentrations were below 5.0 mg/L on three of seven occasions at SC-23 and on four
of seven occasions at SC-CH between June and September 2005. Thus, low dissolved
oxygen continued to be a water quality problem in Smith Creek. The North Carolina
turbidity standard for estuarine waters (25 NTU) was not exceeded during 2005, an
improvement over last year. Nutrient concentrations remained similar to last year's
levels, and algal blooms exceeding the State standard were not found in 2005.
However, lesser algal blooms of 35 µg/L and 25 µg/L occurred at SC-23 and SC-CH,
respectively, in August, and a bloom of 25 µg/L occurred at SC-23 in July. Fecal
coliform bacteria concentrations were above 200 CFU/100 mL on only one occasion (at
SC-CH), an improvement over the past two years. BOD5 was sampled at SC-CH, with
a mean value of 1.4 mg/L and a median value of 1.5 mg/L, similar to last year.
Whiskey Creek – Whiskey Creek is the southernmost large tidal creek in New Hanover
County that drains into the ICW. Five stations are sampled from shore along this creek.
Whiskey Creek had moderate nutrient loading but generally low chlorophyll a
concentrations in 2004-2005, with the exception of one minor algal bloom. Dissolved
oxygen concentrations were below the State standard on only one of 12 occasions at
both WC-MLR and WC-AB in 2004-2005, and high turbidity was not a problem. Fecal
coliform bacteria were not sampled in 2004-2005 in Whiskey 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 2004-2005 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 as poor water quality. Five of the six stations in Burnt Mill Creek were
5
rated as poor in 2005, 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 poor. The lower tidal stations in Hewletts Creek were rated good to fair for fecal
coliforms; the middle stations as fair, and two upper tidal stations were poor and fair,
respectively. The non-tidal freshwater stations in the Hewletts Creek watershed were
poor throughout. The uppermost two stations in Howe Creek were rated poor and fair,
respectively, and the lower three were rated good. Lower Motts Creek was rated poor,
and the two stations in Smith Creek were good and fair, respectively. We also list our
ratings for chlorophyll a, dissolved oxygen and turbidity in Appendix B. Fecal coliform
bacterial conditions for the entire Wilmington City and New Hanover County
Watersheds system (40 sites) showed 30% to be in good condition, 20% in fair
condition, and 50% in poor condition. Dissolved oxygen conditions system-wide (54
sites) showed 59% of the sites were in good condition, 9% were in poor condition, and
32% were in poor condition.
Sediment Fecal Bacteria Study - A study was performed to determine the abundance of
fecal bacteria in Bradley Creek sediments and to see if their concentrations were
related to sediment phosphorus (P), sediment carbon (C), salinity and water
temperature. The concentrations of fecal indicator bacteria in sediments of Bradley
Creek were highly variable, spanning over 3 orders of magnitude. Fecal coliform
concentrations had a geometric mean of 179 CFU/cm2 (std. dev. = 411, range = 0 –
3,230) in a total of 154 samples. This geometric mean value corresponds to a value of
179 CFU/100 ml if all these bacteria were suspended in a water column 1 meter deep,
a value just below that required to close the water to human body contact (200
CFU/100 ml). The regulatory standard for shellfishing is much lower, 14 CFU/100 ml;
113 of the 154 samples exceeded this value using analogous assumptions. Fecal
2
enterococcus concentrations had a geometric mean value of 285 CFU/cm (std. dev. =
433, range = 0-1726). This geometric mean value corresponds to a value of 285 CFU
per 100 ml if all these bacteria were suspended in a water column 1 meter deep, a
value well above that required to close the water to human body contact (33 CFU/100
ml). Thus, the levels of fecal indicator bacteria measured in Bradley Creek sediments
frequently represent serious potential problems for human uses of these waters. We
further note that mixing will add the sediment fecal bacteria to the high levels already
present in the water column of Bradley Creek.
Sediment fecal coliform bacteria were negatively correlated with salinity and positively
correlated with water temperature, but enterococcus had no significant relationship to
these factors. Rainfall in the 24-hour period preceding sampling was also significantly
related to fecal coliform counts. Laboratory experiments showed that both fecal
coliform bacteria and enterococcus bacteria counts were positively related to increasing
concentrations of usable (or bioavailable) carbon (dextrose). However, only
enterococcus was significantly correlated to sediment P concentrations, and only when
background P concentrations were low. Bioavailable C is abundant in stormwater
runoff. Because of this, and the fact that sediment fecal bacteria counts were positively
related to rainfall, we conclude that storm water runoff is the most significant factor
driving sediment contamination.
6
Evaluation of Oyster Characteristics in Pages, Howe, and Hewletts Creeks – The
UNCW Benthic Ecology Laboratory examined oyster characteristics and reef
characteristics in Pages, Howe, and Hewletts Creeks, but there were few clear patterns
indicating a difference in oyster health among the creeks. We had expected Pages
Creek to show characteristics of healthier oysters or better-developed reefs compared
to either Hewletts or Howe Creeks. Percent shell coverage was greatest in Pages
Creek, on average ~10% greater coverage than oyster reefs in Hewletts Creek and
~28% greater coverage than oyster reefs in Howe Creek. It seems likely that that lower
coverage of exposed shell in Howe and Hewletts Creeks may be a function of
increased suspended solids and subsequent sedimentation compared to Pages Creek,
rather than increased oyster production in Pages Creek. Howe Creek showed the
greatest oyster density of the three creeks and no apparent difference in oyster size
was seen among the creeks. Where we did detect differences in reef height and shell
cover, these differences supported the idea that greater sedimentation impacted
Hewletts and Howe Creeks compared to Pages Creek. While we know that water
quality in Hewletts Creek has suffered for some time, the current data does not provide
evidence for population differences among the creeks. However, oyster population
measures may reflect regional conditions more than local creek conditions because of
interchange among the creek systems through the IntraCoastal Waterway. Even with
similar densities and reef form, differences may be apparent with physiological or
condition measures such as tissue weight and disease incidence. Currently we are
evaluating the disease intensity for oysters in these three target creeks and will
compare disease intensity and condition of these oyster populations.
7
Table of Contents
1.0
1.1
2.0
3.0
4.0
5.0
6.0
6.1
7.0
7.1
8.0
9.0
10.0
11.0
12.0
13.0
14.0
15.0
16.0
17.0
18.0
19.0
20.0
Introduction
8
Methods
8
Barnards Creek
10
Bradley Creek
13
Burnt Mill Creek
16
Futch Creek
22
Greenfield Lake
26
Preliminary Assessment of Greenfield Lake Restoration Measures 30
Hewletts Creek
40
The 2005 Major Sewage Spill in Hewletts Creek
47
Howe Creek
52
Motts Creek
56
Pages Creek
59
Smith Creek
61
Whiskey Creek
64
Sediment Fecal Bacteria Study
67
Evaluation of Oyster Characteristics
78
References Cited
85
Acknowledgments
87
Appendix A: Selected N.C. water quality standards
88
Appendix B: UNCW Watershed Station Ratings Based on DWQ Chemical
Standards
89
Appendix C: GPS coordinates for the New Hanover County Tidal Creek
and Wilmington Watersheds Program sampling stations
91
Appendix D: UNCW reports and papers related to tidal creeks
93
8
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.
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 2004 - July 2005 in the tidal creek
complex and January - September 2005 in the City of Wilmington watersheds. The
UNCW Aquatic Ecology Laboratory is also involved with a project headed up by North
Carolina State University (NCSU) and funded through the EPA 319 Grant program that
is designed to provide stream restoration to Burnt Mill Creek. Thus, three stations have
been added to the Burnt Mill creek sampling matrix under this program.
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), total suspended solids (TSS) 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 650 MDS 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) and for
laboratory chlorophyll a measurements. The light attenuation coefficient k was
determined (at locations where depth permitted), from data collected on site using
vertical profiles obtained by a Li-Cor LI-1000 integrator interfaced with a Li-Cor LI-193S
spherical quantum sensor.
9
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 2005. 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) and for a
constructed wetland on Kerr Avenue (at the headwaters area of 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).
10
2.0 Barnards Creek
The water quality of lower Barnard’s Creek is 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 2005 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 an average salinity of 5.7 ppt with a range of 2.0-11.4 ppt. This station
had dissolved oxygen levels ranging from 2.8-3.5 from June through September.
Concentrations of nutrients (total nitrogen, nitrate, ammonium, orthophosphate and total
phosphorus) were among the highest in the Wilmington area (Table 2.1). Turbidity on
average was moderate (16 NTU), and did not exceed the state standard for estuarine
waters of 25 NTU. Total suspended solids concentrations were among 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 mg/L and a mean of 1.4 mg/L, which was down from the BOD5
concentrations found in previous years (Mallin et al. 2003; 2004). Median and mean
BOD20 in 2005 were 4.4 and 5.0 mg/L, not problematic values. Fecal coliform counts
exceeded the state standard on two of seven occasions for a 29% non-compliance rate,
slightly poorer than the previous year. Thus, this station can be considered impaired by
low dissolved oxygen and fecal coliform bacteria, with comparatively high nutrient
concentrations as well.
11
Table 2.1. Mean and standard deviation of water quality parameters in Barnards Creek
watershed, January - September 2005. Fecal coliforms as geometric mean; N/P ratio as
median (n = 7 for all parameters).
_____________________________________________________________________
Parameter
BNC-RR
_____________________________________________________________________
DO (mg/L)
5.1 (2.9)
Turbidity (NTU)
16 (5)
TSS (mg/L)
18.4 (8.3)
Nitrate (mg/L)
0.217 (0.106)
Ammonium (mg/L)
0.161 (0.129)
TN (mg/L)
1.424 (0.367)
Phosphate (mg/L)
0.040 (0.046)
TP (mg/L)
0.146 (0.080)
N/P molar ratio
35.4
Chlorophyll a (µg/L)
6.3 (6.0)
BOD5
1.4 (0.7)
BOD20
5.7 (1.3)
Fecal coliform bacteria (/100 mL)
105
_____________________________________________________________________
12
13
3.0 Bradley Creek
The Bradley Creek watershed has been a principal location for Clean Water Trust Fund
mitigation activities, including the purchase and renovation of Airlie Gardens by the
County. The development of the former Duck Haven property bordering Eastwood
Road is of great concern in terms of its potential water quality impacts to the creek.
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 2004-2005 (Table 3.1). The
standard of 25 NTU was not exceeded during our sampling. There were only minor
problems with low dissolved oxygen (hypoxia), with BC-NB having DO < 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 2004-July 2005. 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
31.3 (2.3)
26.3-33.8
3 (3)
0-10
7.3 (2.0)
4.3-10.1
NA
BC-SB
9.7 (11.0)
0.2-29.6
6 (5)
0-16
7.4 (2.0)
4.8-10.8
NA
BC-SBU
0.1 (0.0)
0.1-0.1
2 (1)
0-5
7.2 (1.7)
4.5-10.9
NA
BC-NB
22.8 (10.0)
4.6-32.7
4 (3)
0-8
7.2 (2.6)
2.9-10.9
NA
BC-NBU
0.1 (0.0)
0.1-0.2
9 (14)
0-52
7.4 (0.8)
6.0-8.4
NA
BC-CR
0.1 (0.0)
0.1-0.1
1 (2)
0-8
7.8 (0.7)
6.0-8.4
NA
BC-CA
0.1 (0.1)
6 (5)
5.1 (2.7)
1207
0.1-0.1
1-16
2.3-9.1
210-3400
_____________________________________________________________________
NA = not analyzed
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
14
collections for an 86% exceedence rate (Table 3.1). We consider BC-CA to have poor
water quality in terms of fecal coliform bacteria 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 2004-2005, except for a minor bloom in April at BC-SB (26 µg/L) and a major
bloom (52 µg/L) in July at that station (Table 3.2).
Table 3.2. Nutrient and chlorophyll a data at Bradley Creek sampling stations, August
2004-July 2005. Data as mean (SD) / range, nutrients in mg/L, chlorophyll a as µg/L.
_____________________________________________________________________
Station
Nitrate
Ammonium
Orthophosphate
Chlorophyll a
_____________________________________________________________________
BC-76
BC-SB
BC-SBU
BC-NB
BC-NBU
BC-CR
BC-CA
0.011 (0.008)0.019 (0.009)0.008 (0.003)1.9 (2.1)
0.003-0.033
0.014-0.042
0.005-0.016
0.2-6.4
0.034 (0.030)0.026 (0.018)0.011 (0.006)8.9 (15.5)
0.005-0.090
0.014-0.073
0.005-0.025
0.3-52.0
0.076 (0.025)
0.037-0.132
0.1-2.7
NA
0.012 (0.007)0.8 (0.8)
0.004-0.023
0.024 (0.027)0.033 (0.044)0.010 (0.005)3.0 (3.6)
0.004-0.088
0.014-0.158
0.005-0.021
0.3-11.6
0.098 (0.065)
0.047-0.291
NA
0.003 (0.002)0.6 (0.5)
0.001-0.009
0.0-1.6
0.267 (0.091)
0.071-0.478
NA
0.005 (0.002)0.6 (0.8)
0.001-0.009
0.0-2.4
0.140 (0.209)0.164 (0.124)0.027 (0.022)3.3 (2.8)
0.030-0.600
0.020-0.420
0.005-0.050
0.9-8.7
_____________________________________________________________________
NA = not analyzed
15
Figure 3.1. Bradley Creek watershed and sampling sites.
16
4.0 Burnt Mill Creek
Since 1997 the Burnt Mill Creek watershed (Fig. 4.1) has been sampled just upstream
of Ann McCrary Pond on Randall Parkway (BMC-AP1), about 40 m downstream of the
pond outfall (BMC-AP3). 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).
In 2005 sampling began on the inflow (BMC-KA1) and outflow (BMC-KA3) channels of
the Kerr Avenue constructed wetland (Fig. 4.1). This new sampling began as a part of
a larger project (with NCSU funded by the EPA 319 Program) to provide stream
restoration to Burnt Mill Creek. Construction of the 0.7 acre Kerr Avenue Wetland was
funded by the N.C. Wetlands Restoration Program, now known as the Ecosystem
Enhancement Program. Wetland construction was completed in November 2000 and
the first aquatic macrophyte planting (sponsored by Cape Fear River Watch) occurred
later that month (various rushes, sedge, pickerelweed, lizard’s tail, water tupelo, wax
myrtle, black gum, pond pine, bald cypress, etc.). Since then there have been many
supplemental plantings as well as tree donations. The vegetation coverage is presently
so dense that macrophytes from this site have been transplanted into other wetland
restoration sites. The wetland has a forebay to collect sediment, and the system is
designed to retain and treat the first 0.5 inches of a rainfall event before an overflow
channel is utilized. This Best Management Practice (BMP) lies in the headwaters of
Burnt Mill Creek, which is on the State 303(d) list for poor biological condition. Another
new station is located along the main stem of the creek in the Wallace Park area (BMCWP) and an older station is also on the creek at the bridge at Princess Place (BMC-PP
- Fig. 4.1).
Kerr Avenue Wetland: This represents the first statistically comparative data useful for
assessing the efficacy of this pond as a pollutant removal device. Results of the seven
sampling trips showed that turbidity and suspended solids were low both entering and
leaving the pond, with no significant difference (Table 4.1). One nutrient parameter,
ammonium, was significantly lowered by the pond, while there was no difference in the
other nutrient species (which were not in high concentrations entering the pond). BOD5
and BOD20 were not elevated entering the pond and there was no significant difference
in concentrations leaving the pond. Fecal coliform bacteria were somewhat elevated
entering the pond, and had similar concentrations leaving the pond. The presence of a
number of dumpsters surrounding the site, and consequent small mammal foraging and
defecating, may be a localized source of fecal coliform bacteria and organic nutrients.
Ann McCrary Pond: Turbidity and suspended solids concentrations entering and leaving
the pond were low to moderate. Fecal coliform concentrations entering Ann McCrary
17
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 2005 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 June and August, but three major (chlorophyll a > 40 µg/L)
and two minor algal blooms (chlorophyll a > 20 µg/L) at BMC-AP3, the largest amount
of bloom activity we have witnessed since the inception of this project in 1997. The
efficiency of Ann McCrary 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.
Lower Burnt Mill Creek: Both the Wallace Park (BMC-WP) and 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)
three of six times at BMC-WP and four of seven times at BMC-PP. No problems were
seen with turbidity or suspended solids. Nutrients were unremarkable at either site
except for an unusual maximum of TN (which was mainly organic nitrogen) at BMC-PP
in May. No algal blooms exceeded the State standard for chlorophyll a at Wallace
Park, although an unusually high pulse of chlorophyll a (646 µg/L) occurred at Princess
Place in May, when the field team reported the waters there to be unusually brown and
foamy. This bloom accounted for the unusually high TN levels (TP levels were also
elevated to 0.230 mg/L).
An important issue, from a public health perspective, was the excessive fecal coliform
counts, which maintained geometric means (958 CFU/100 mL at BMC-WP and 479
CFU/100 mL at BMC-PP) 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
six months at Wallace Park and five of seven months at Princess Place, respectively. 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). BOD5 and BOD20 analyses
were performed at Wallace Park, with no unusually high concentrations reported.
18
Table 4.1. Mean and (standard deviation) of water quality parameters in upper Burnt
Mill Creek, Jan. – Sep. 2005. Fecal coliforms as geometric mean; N/P as median.
_____________________________________________________________________
Parameter
KA-1
KA-3
BMC-AP1
BMC-AP3
_____________________________________________________________________
DO (mg/L)
4.1 (1.2)
4.9 (1.3)
7.5 (0.8)
10.1 (1.3)*
Cond. (µS/cm)
333 (20)
358 (32)
259 (62)
242 (20)
pH
6.7 (0.4)
6.8 (0.2)
7.3 (0.4)
7.7 (0.2)*
Turbidity (NTU)
6 (3)
5 (2)
11 (19)
6 (3)
TSS (mg/L)
3.5 (0.5)
3.3 (1.0)
9.1 (15.9)13.9 (10.2)
Nitrate (mg/L)
0.052 (0.031) 0.054 (0.034) 0.117 (0.108) 0.076 (0.083)
Ammonium (mg/L) 0.177 (0.084) 0.023 (0.008)* 0.051 (0.036) 0.036 (0.017)
TN (mg/L)
0.717 (0.181) 0.533 (0.207) 0.676 (0.191) 0.993 (0.362)
OrthoPhos. (mg/L) 0.006 (0.002) 0.007 (0.003) 0.019 (0.022) 0.007 (0.004)
TP (mg/L)
0.053 (0.026) 0.062 (0.016) 0.061 (0.043) 0.070 (0.046)
N/P molar ratio
110.7
26.6
37.6
35.4
Chlor. a (µg/L)
0.7 (0.7)
4.8 (5.5)
8.4 (8.6)
45.4 (40.6)
Fec. col. (/100 mL) 587
436
793
112*
BOD5
1.1 (0.6)
1.2 (0.4)
NA
NA
BOD20
4.3 (1.9)
4.1 (1.1)
NA
NA
_____________________________________________________________________
* Indicates statistically significant difference between inflow and outflow at p<0.05
NA = not analyzed
Table 4.2. Mean and (standard deviation) of water quality parameters in lower Burnt
Mill Creek, Jan. – Sep. 2005. Fecal coliforms as geometric mean; N/P as median.
_____________________________________________________________________
Parameter
BMC-WP
BMC-PP
_____________________________________________________________________
DO (mg/L)
5.0 (1.2)
5.5 (2.7)
Cond. (µS/cm)
358 (18)
353 (40)
pH
7.0 (0.1)
7.1 (0.2)
Turbidity (NTU)
8 (3)
6 (3)
TSS (mg/L)
6.5 (4.0)
8.9 (9.7)
Nitrate (mg/L)
0.143 (0.091)
0.116 (0.084)
Ammonium (mg/L)
0.108 (0.040)0.091 (0.055)
TN (mg/L)
0.872 (0.174)
1.697 (2.245)
OrthoPhos. (mg/L)
0.008 (0.003)
0.012 (0.009)
TP (mg/L)
0.067 (0.021)
0.107 (0.059)
N/P molar ratio
51.4
30.5
Chlor. a (µg/L)
7.2 (4.4)
98.3 (241.6)
Fec. col. (/100 mL)
958
479
BOD5
1.4 (0.5)
NA
BOD20
5.5 (1.2)
NA
_____________________________________________________________________
NA = not analyzed
Figure 4.1. Burnt Mill Creek watershed and sampling sites.
19
20
Sediment Metals and PAH Concentrations
As part of the stream restoration effort funded through NCSU and EPA 319 program, we
collected sediment samples on one occasion throughout Burnt Mill Creek for analysis of
sediment metals and polycyclic aromatic hydrocarbons (PAHs). The State of North
Carolina has no official guidelines for sediment concentrations of metals and organic
pollutants in reference to protection of invertebrates, fish and wildlife. However, academic
researchers (Long et al. 1995) have produced guidelines (Appendix D) based on extensive
field and laboratory testing that are used by the US Environmental Protection Agency in
their National Coastal Condition Report II (US EPA 2004).
Table 4.3. Guideline values for sediment metals and organic pollutant concentrations
(ppm, or µg/g, dry wt.) potentially harmful to aquatic life (Long et al. 1995; U.S. EPA
2004). ERL = (Effects range low). Concentrations below the ERL are those in which
harmful effects on aquatic communities are rarely observed. ERM = (Effects range
median). Concentrations above the ERM are those in which harmful effects would
frequently occur. Concentrations between the ERL and ERM are those in which
harmful effects occasionally occur.
_____________________________________________________________________
Metal
ERL
ERM
_____________________________________________________________________
Arsenic (As)
8.2
70.0
Cadmium (Cd)
1.2
9.6
Chromium (Cr)
81.0
370.0
Copper (Cu)
34.0
270.0
Lead (Pb)
46.7
218.0
Mercury (Hg)
0.15
0.71
Nickel (Ni)
20.9
51.6
Silver (Ag)
1.0
3.7
Zinc (Zn)
150.0
410.0
Total PCBs
0.0227
0.1800
Total PAHs
4.02
44.80
Total DDT
0.0016
0.0461
_____________________________________________________________________
Most of the stations had sediment metals concentrations that were well below levels
considered potentially toxic to benthic organisms. An exception was lead, which
exceeded the ERL (Table 4.3) at the Wallace Park station BMC-WP (Table 4.4). Lead
concentrations at BMC-KA1 and Princess Place (BMC-PP) approached harmful
concentrations but did not exceed them. Mercury did not exceed the ERL but
concentrations were close to it at BMC-PP (Table 4.4). All of the PAH sediment
samples exceeded the ERM (Table 4.4).
21
Table 4.4. Concentrations of sediment metals and polycyclic aromatic hydrocarbons
(PAHs) in Burnt Mill Creek, 2005 (as mg/kg = ppm). Concentrations in bold type
exceed the level at which harmful effects to benthic organisms may occur, and italicized
concentrations are near potentially harmful levels (see Table 4.3 for more detail).
_____________________________________________________________________
Parameter KA1
KA3
AP1
AP3
WP
PP
_____________________________________________________________________
Antimony
0.147
<0.077
<0.078
<0.90
<0.08
0.127
Arsenic
<0.125
<0.125
<0.128
<0.127
<0.143
<0.151
Beryllium
0.060
0.026
<0.026
0.026
0.270
0.248
Cadmium
0.172
0.039
<0.026
0.067
0.727
0.471
Chromium 4.740
0.979
0.211
1.450
11.60
6.93
Copper
7.48
7.69
0.834
3.25
20.80
8.73
Lead
24.20
4.38
2.08
8.49
95.60
33.90
Mercury
<0.003
<0.003
<0.003
0.006
0.134
0.094
Nickel
3.910
0.701
0.224
1.150
2.830
3.040
Selenium
0.132
<0.127
<0.128
0.133
<0.151
<0.140
Silver
<0.125
<0.127
<0.128
<0.127
<0.143
<0.151
Thallium
<0.026
<0.026
<0.020
0.025
0.063
<0.060
Zinc
48.80
14.00
5.38
20.50
74.20
30.40
Total PAH 8,873
8,847
287
BDL
2,202
115
TN
3,475
3,281
138
238
2.0
2.3
TP
120.0
74.2
27.0
45.3
474.0
352.0
TOC
79.4
46.5
39.7
99.5
431.0
408.0
_____________________________________________________________________
BDL = below detection limit
Polycyclic aromatic hydrocarbons (PAHs) are organic compounds with a fused ring
structure. PAHs with two to five rings are of considerable environmental concern. They
are compounds of crude and refined petroleum products and coal and are also
produced by incomplete combustion of organic materials (US EPA 2000). They are
characteristic of urban runoff as they derive from tire wear, automobile oil and exhaust
particles, and leaching of asphalt roads. Other sources include domestic and industrial
waste discharge, atmospheric deposition, and spilled fossil fuels. They are
carcinogenic to humans, and bioconcentrate in aquatic animals. In these organisms
they form carcinogenic and mutagenic intermediaries and cause tumors in fish (US
EPA 2000).
22
5.0 Futch Creek
Six stations have been sampled in Futch Creek since 1993. During 1995 and 1996 two
channels were dredged in the mouth of Futch Creek (Fig. 5.1) to improve circulation
from the ICW and hopefully reduce fecal coliform bacterial concentrations. The result
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 2004-2005, there were no incidences of creek
stations having turbidity levels exceeding the state standard of 25 NTU (Table 5.1).
Low dissolved oxygen, was not a problem except for July 2005, when concentrations at
four sites dropped below the State standard (Table 5.1; Appendix B).
Table 5.1. Physical parameters at Futch Creek sampling stations, August 2004 - July
2005. Data given as mean (SD) / range.
_____________________________________________________________________
Station
Salinity
Turbidity
Light attenuation Dissolved oxygen
(ppt)
(NTU)
(k/m)
(mg/L)
_____________________________________________________________________
FC-4
32.1 (6.1)
13.0-35.0
4 (3)
0-9
1.0 (1.3)
0.3-3.7
7.9 (2.1)
5.4-11.6
FC-6
30.8 (7.7)
6.6-34.5
5 (5)
0-16
1.5 (1.9)
0.3-5.6
7.7 (2.2)
5.3-11.6
FC-8
29.8 (7.6)
6.7-34.5
5 (5)
0-16
1.3 (1.5)
0.2-4.8
7.5 (2.2)
4.9-11.5
FC-13
25.7 (8.3)
1.2-30.6
6 (7)
0-22
1.5 (1.8)
0.2-6.2
7.1 (2.4)
4.1-11.3
FC-17
19.3 (10.0)
0.1-29.3
7 (6)
1-23
1.6 (1.3)
0.5-4.2
7.2 (2.5)
3.6-11.2
FOY
25.1 (9.1)
5 (4)
1.7 (2.1)
7.5 (2.7)
0.1-33.2
0-10
0.5-6.4
4.0-11.6
_____________________________________________________________________
Nutrient concentrations in Futch Creek remained generally low, with a general decrease
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 drought of 2005 would lead to less surface runoff and
groundwater pumping of nitrate. The creek was free from algal blooms during our
sampling visits (Table 5.2), even in the upper stations.
23
Table 5.2. Nutrient and chlorophyll a data from Futch Creek, August 2004-July 2005.
Data as mean (SD) / range, nutrients in mg/L, chlorophyll a as µg/L.
_____________________________________________________________________
Station
Nitrate
Ammonium
Orthophosphate
Chlorophyll a
_____________________________________________________________________
FC-4
FC-6
FC-8
FC-13
FC-17
0.011 (0.013)0.023 (0.012)0.008 (0.004)1.2 (1.4)
0.003-0.050
0.014-0.045
0.005-0.019
0.1-3.9
0.012 (0.012)
0.003-0.049
NA
0.009 (0.005)1.2 (1.3)
0.005-0.022
0.1-3.6
0.016 (0.013)
0.004-0.051
NA
0.011 (0.005)1.6 (1.8)
0.006-0.023
0.2-5.1
0.035 (0.029)
0.005-0.103
NA
0.013 (0.007)2.5 (2.7)
0.005-0.030
0.2-8.3
0.057 (0.055)0.035 (0.025)0.013 (0.008)2.8 (2.9)
0.008-0.198
0.014-0.081
0.004-0.036
0.2-8.4
FOY
0.019 (0.011)0.029 (0.022)0.009 (0.003)1.5 (1.3)
0.004-0.047
0.014-0.076
0.005-0.016
0.3-4.4
_____________________________________________________________________
NA = not analyzed
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
2004-2005 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, with only one station (FC-17)
having a single incident of fecal coliform counts exceeding 200 CFU/mL. There was a
slight improvement in microbiological water quality at the upper stations compared with
the previous year (Fig. 5.2), probably a result of less runoff during this drought period.
All stations had geometric mean fecal coliform counts that were well within safe limits
for human contact waters (Appendix B). In summary, Futch Creek had the best water
quality of all watersheds sampled for this report (Appendix B).
24
Figure 5.1. Futch Creek watershed and sampling sites.
25
Table 5.3. Futch Creek fecal coliform bacteria data, including percent of samples
exceeding 43 CFU per 100 mL, August 2004 - July 2005.
_____________________________________________________________________
Station
FC-4 FC-6 FC-8 FC-13 FC-17 FOY
Geomean (CFU/100 mL)
1
3
4
16
37
9
% > 43 /100ml
9
9
9
33
27
17
_____________________________________________________________________
Figure 5.2 Geometric mean fecal coliform bacteria counts over time
at selected Futch Creek stations, 1994-2005
Fecal coliforms (CFU/100mL)
250
Channel dredging in
mouth of creek
200
150
100
50
0
1995
1996
1997
1998
1999
2000
2001
2002
2003
Year
FC8
FC13
FC17
FOY
2004
2005
26
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 hypoxia, with GL-LB
(creek at Lake Branch Drive) and GL-LC (creek beside Lakeshore Commons) both
showing average concentrations below the state standard (DO < 5.0 mg/L). Dissolved
oxygen levels periodically were 1.0 mg/L or less on three occasions at GL-LB 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 GLJRB (Jumping Run Branch) (Table 6.1). Ammonium concentrations were highest at
GL-LB, and generally similar across the other two tributary stations. Phosphorus
concentrations were similar at these 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, three of seven times at GL-LC, and five of seven times at GLJRB. There was one major algal bloom in June at GL-JRB, with a chlorophyll a level of
40.4 µg/L. Lesser blooms of 25.5 and 34 µg/L occurred at GL-JRB and GL-LC,
respectively, in September, and a bloom of 30 µg/L at GL-LB in March.
Table 6.1. Mean and (standard deviation) of water quality parameters in tributary
stations of Greenfield Lake, January - September 2005. 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)
5.7 (2.0)
2.7 (3.2)
3.5 (1.5)
Turbidity (NTU)
1 (1)
2 (2)
2 (2)
TSS (mg/L)
2.7 (0.8)
2.2 (0.9)
2.8 (1.5)
Nitrate (mg/L)
0.056 (0.019)0.123 (0.099)0.177 (0.149)
Ammonium (mg/L)
0.054 (0.024)
0.250 (0.122)0.133 (0.069)
TN (mg/L)
0.796 (0.170)
0.956 (0.250)1.033 (0.282)
Orthophosphate (mg/L)
0.017 (0.013)
0.016 (0.013)0.020 (0.015)
TP (mg/L)
0.089 (0.069)
0.089 (0.039)0.080 (0.041)
N/P molar ratio
20.5
75.3
46.2
Fec. col. (/100 mL)
353
217
325
Chlor. a (µg/L)
13.2 (14.6)
6.5 (10.5)
7.5 (12.1)
_____________________________________________________________________
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
was only a problem at GL-2340, with general improvement shown over the last two
years (see Section 6.1). Turbidity and suspended solids were low to moderate at these
three sites, except for high TSS (52 mg/L) in September at GL-2340. Fecal coliform
concentrations were only problematic at GL-P (Appendix B) with two of seven samples
exceeding the State standard in 2005.
27
Nitrogen concentrations were generally highest at GL-P, followed by GL-2340, while
phosphorus concentrations were highest at GL-YD. (Table 6.2). There were TN
maxima of 3.5 mg/L at GL-P in June and 2.9 mg/L at GL-2340 in May. There were low
chlorophyll a concentrations during those periods so these maxima were likely a result
of high summer ammonium and organic N resulting from decaying aquatic macrophyte
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 somewhat below the Redfield ratio, indicating nitrogen
limitation. Our previous bioassay work indicated that nitrogen was usually the limiting
nutrient in this lake (Mallin et al. 1999). Two major and one minor algal bloom occurred
at GL-P, three major blooms occurred at GL-2340, and two major and one minor bloom
occurred at GL-YD. The magnitude of the major in-lake blooms ranged from 47-110
µg/L of chlorophyll a.
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. Seven
algal blooms exceeding the state standard of 40 µg/L were recorded in our sampling
during 2005 (an increase over the previous year), but the former heavy surface scum of
duckweed was removed due to remedial action by the City (see Section 6.1). Thus,
during 2005 Greenfield Lake was impaired by algal blooms, high fecal coliform counts
and low dissolved oxygen concentrations, although there was definite improvement with
the latter parameter. 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; 2005).
28
Table 6.2. Mean and (standard deviation) of water quality parameters in Greenfield
Lake sampling stations, January - September 2005. 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)
7.9 (4.8)
9.3 (3.6)
7.8 (3.2)
Turbidity (NTU)
5 (10)
1 (2)
3 (4)
TSS (mg/L)
10.9 (18.3)
5.7 (5.1)
6.8 (7.4)
Nitrate (mg/L)
0.075 (0.059)0.046 (0.069)0.081 (0.106)
Ammonium (mg/L)
0.070 (0.093)
0.029 (0.011)0.043 (0.045)
TN (mg/L)
1.416 (0.759)
1.134 (0.397)1.466 (0.979)
OrthopPhosphate (mg/L) 0.016 (0.012)
0.021 (0.016)0.018 (0.017)
TP (mg/L)
0.049 (0.026)
0.139 (0.127)0.127 (0.132)
N/P molar ratio
14.4
6.1
12.2
Fec. col. (/100 mL)
79
41
165
Chlor. a (µg/L)
43.0 (48.0)
34.2 (41.4)
24.9 (27.3)
____________________________________________________________________
29
30
6.1 A Preliminary Assessment of the Efficacy of the 2005 Greenfield Lake
Restoration Measures
Michael A. Mallin and Virginia L. Johnson
Center for Marine Science
University of North Carolina Wilmington
Introduction
Greenfield Lake is a 37 ha blackwater system located in the City of Wilmington, North
Carolina. It was first dammed and filled as a millpond in 1750, and purchased for a city
park in 1925. It has an average depth of 1.2-1.5 m, it is about 8,530 m around the
shoreline, and its watershed drains approximately 1025 ha (2532 acres). The lake has
one outfall, but is fed by six perennial inflowing streams (as well as intermittent ditches).
The lake is surrounded by a watershed that is comprised mainly of residential, office,
institutional and commercial areas, with an overall watershed impervious surface
coverage of 30% (Matt Hayes, City of Wilmington, personal communication).
In recent decades a number of water quality problems have become chronic within the
lake, including high fecal coliform bacterial counts, low dissolved oxygen problems,
nuisance aquatic macrophyte growths, algal blooms and fish kills. Some of these
problems are typically related to eutrophication, a process driven by loading of
excessive nutrients to a body of water. The State of North Carolina Division of Water
Quality considers the lake to have a problem with aquatic weeds (NCDENR 2005).
Periodic phytoplankton blooms have occurred in spring, summer and fall. Some of the
most frequent bloom forming taxa are the cyanobacterium Anabaena cylindrica and the
chlorophytes Spirogyra and Mougeotia spp. The free-floating macrophyte Lemna sp.
(duckweed) is frequently observed on the surface, and below a massive Lemna bloom
in summer 2004 dissolved oxygen concentrations at the park station were nearly
anoxic. In-situ monitoring instruments have demonstrated that dissolved oxygen
concentrations can decrease by as much as 45% at night compared with daytime DO
measurements.
In 2005 several steps were taken by the City of Wilmington to restore viability to the
lake (David Mayes, City of Wilmington Stormwater Services, personal communication).
During February one thousand sterile grass carp were introduced to the lake to control
(by grazing) the overabundant aquatic macrophytes. During that same month four
SolarBee water circulation systems were installed in the lake to improve circulation and
force dissolved oxygen from the surface downward toward the bottom. Finally, from
April through June a contract firm applied the herbicide Sonar to further reduce the
amount of aquatic macrophytes.
Since 1998 the University of North Carolina Wilmington's Aquatic Ecology Laboratory,
located at the Center for Marine Science, has been performing water quality sampling
and associated experiments on Greenfield Lake. The City of Wilmington Engineering
Department has funded this effort. Monitoring of various physical, chemical, and
biological parameters has occurred monthly. These data allow us to perform a
31
preliminary assessment of the effectiveness of the City's lake restoration efforts by
comparing summer data from 2003 and 2004 (before restoration efforts) with data from
summer 2005 (after restoration efforts have begun).
Results
To assess the results so far we have chosen several parameters to examine over time.
One parameter that is not quantified is surface coverage by nuisance macrophyte
vegetation. In the summers of 2003 and 2004 extensive mats of duckweed (Lemna
sp.), mixed with algae and other vegetation covered large areas of the lake's surface,
with visible estimates for some coves exceeding 95% coverage. In summer of 2005
surface coverage was minimal; with most lake areas 95% clear of surface mats.
Dissolved oxygen: During 2003 and 2004 hypoxia (DO < 4.0 mg/L) was common in
surface waters (Figs. 6.2a and 6.2b. Areas beneath thick Lemna mats were anoxic or
nearly so, especially at GL-P, the main Park area (Fig. 6.2a). Following the onset of
herbicide addition in April 2005, the May DO showed a distinct decrease; however, it
subsequently rose in June and remained at or above the State standard of 5 mg/L
through the rest of the summer (Fig. 6.2b).
Turbidity: Turbidity was not excessive in the lake during the two years prior to
restoration efforts (Fig. 6.3). It remained low following these efforts, except for a pulse
up to approximately 30 NTU at GL-2340 in September. However, even this value is
below the freshwater State standard of 50 NTU.
Ammonium: Ammonia/ammonium is a common degradation product of organic
material, and is an excretory product of fish and other organisms. The addition of grass
carp and the herbicide usage did not appear to raise ammonium concentrations in the
lake (Fig. 6.4). Potentially some of the ammonium produced may have been utilized by
phytoplankton.
Nitrate: Nitrate is an inorganic form of nitrogen that is known to enter the lake during
rainfall and runoff periods (Mallin et al. 2002). The concentrations of nitrate in the lake
do not appear to have been influenced by the restoration efforts (Fig. 6.5).
Total nitrogen: Total nitrogen (TN) is a combination of all inorganic and organic forms of
nitrogen. Mean concentrations and concentrations at individual stations appeared to be
unaffected by the restoration efforts (Fig. 6.6).
Orthophosphate: Orthophosphate is the most common inorganic form of phosphorus,
and is utilized as a key nutrient by aquatic macrophytes and phytoplankton.
Orthophosphate was not found at excessive concentrations in the water column either
before or after the restoration effort (Fig. 6.7).
Total phosphorus: Total phosphorus (TP) is a combination of all organic and inorganic
forms of phosphorus in the water. Although a pulse of TP occurred in summer 2005, it
was similar in magnitude to pulses of TP seen in 2003 and 2004 (Fig. 6.8), so the
restoration efforts do not seem to have impacted TP levels in the lake.
32
Chlorophyll a: Chlorophyll a is the principal measure used to estimate phytoplankton
biomass in water bodies. As mentioned above, algal blooms have been a common
occurrence in this lake. However, they are generally patchy in space, usually occurring
at one or two stations at a time (Fig. 6.9a). However, in summer 2005 extensive
phytoplankton blooms occurred at all three in-lake stations, with levels well exceeding
the State standard of 40 µg/L (Figs. 6.9a and 6.9b). Algal blooms are the result of
nutrient inputs, either from outside the lake or from release from decaying material.
Fecal coliform bacteria: Fecal coliform bacteria are commonly used to provide an
estimate of the microbial pollution in a water body. Greenfield Lake is chronically
polluted by high fecal coliform counts, well exceeding the state standard of 200
CFU/100 mL (Figs. 6.10a and 6.10b). In summer 2005 there were particularly large
fecal coliform counts at each in-lake station, though the individual stations did not have
pulses during the same months (Fig. 6.10a).
Discussion
A risk that is taken when applying herbicides to lakes is the creation of biochemical
oxygen demand (BOD) from decomposing organic matter that is a product of dead or
dying plant material. This would serve to drive the lake DO concentrations downward.
However, DO levels in summer 2005 were nearly twice what they were during summers
of 2003 and 2004. It is very likely that the use of the SolarBee circulation systems
maintained elevated DO even when there was an obvious BOD source.
Water column nutrient concentrations did not appear to change notably after the
introduction of grass carp or use of herbicide. Certainly ammonium, an excretory and
decomposition product would be expected to rise following the consumption and death
of large quantities of plant material. Likewise phosphorus did not increase, although it
is a common excretory product. However, ammonium (like orthophosphate) is readily
used as a primary nutrient by phytoplankton. Nutrient addition bioassay experiments
have demonstrated that phytoplankton in this lake is limited by nitrogen (Mallin et al.
1999). It is likely that ammonium produced by fish excretion or dying plant material was
utilized by phytoplankton to produce the excessive algal blooms that characterized the
lake in the summer of 2005. The phytoplankton blooms were dominated by blue green
algae (cyanobacteria) including species containing heterocysts. These species have
the added ability to fix atmospheric nitrogen when phosphorus is replete. Thus, while
large amounts of macrophyte material disappeared from the lake, some of the resultant
nutrients were utilized by phytoplankton to produce the blooms. A potential problem
with algal blooms is that when they die, they become labile forms of organic material, or
BOD. Previous research has demonstrated that chlorophyll a in this lake is strongly
correlated with BOD (Mallin et al. 2005).
The apparent increase in fecal coliform bacteria does not appear to be related to any of
the restoration activities. Fecal coliform bacteria enter the environment from the feces
of warm blooded animals, so it is possible that increases in waterfowl or dogs brought
to the lake by their owners could lead to increased fecal coliform bacteria counts, but
we have no data to support this speculation either way.
33
References Cited
Mallin, M.A., V.L. Johnson, S.H. Ensign and T.A. MacPherson. 2006. Factors
contributing to hypoxia in rivers, lakes and streams. Limnology and Oceanography
51:690-701.
Mallin, M.A., S.H. Ensign, D.C. Parsons and J.F. Merritt. 1999. Environmental quality of
Wilmington and New Hanover County watersheds 1998-1999. CMSR Report 99-02.
Center for Marine Science Research, University of North Carolina at Wilmington,
Wilmington, N.C.
Mallin, M.A., L.B. Cahoon, 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.
NCDENR. 2005. Cape Fear River Basinwide Water Quality Plan (draft). North Carolina
Department of Environment and Natural Resources, Division of Water Quality /
Planning, Raleigh, NC, 27699-1617.
34
Figure 6.2a. Greenfield Lake dissolved oxygen (mg/L) by station,
February 2003-September 2005.
GL-2340
GL-YD
GL-P
Dissolved Oxygen
16
14
12
10
8
6
4
2
2003
Sep
Aug
Jul
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
May
Mar
Jan
Sep
Aug
Jul
Feb
Apr
Jun
0
2004
2005
Figure 6.2b. Greenfield Lake mean dissolved oxygen (mg/L),
February 2003-September 2005.
10
8
6
4
2
2003
2004
Sep
Aug
Jul
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
Apr
0
Feb
Dissolved Oxygen
12
2005
35
Figure 6.3. Greenfield Lake turbidity (NTU) by station,
February 2003-September 2005.
GL-2340
GL-YD
GL-P
35
25
20
15
10
5
2003
2004
2005
Figure 6.4. Greenfield Lake mean ammonium concentrations
(as mg/L), February 2003-September 2005.
0.7
0.6
0.5
0.4
0.3
0.2
0.1
2003
2004
2005
Sep
Aug
Jul
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
Apr
Feb
0
Sep
Aug
Jul
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
Feb
Apr
0
Ammonia
Turbidity
30
36
Figure 6.5. Greenfield Lake nitrate-nitrite (mg/L) by station,
February 2003-September 2005.
GL-2340
GL-YD
GL-P
Nitrate-nitrite
0.60
0.50
0.40
0.30
0.20
0.10
2003
2004
Sep
Aug
Jul
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
Apr
Feb
0.00
2005
Figure 6.6. Greenfield Lake total nitrogen (mg/L) by station,
February 2003-September 2005.
GL-2340
GL-YD
GL-P
12.0
8.0
6.0
4.0
2.0
2003
2004
2005
Sep
Aug
Jul
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
Apr
0.0
Feb
Total nitrogen
10.0
37
Figure 6.7. Greenfield Lake orthophosphate (mg/L) by station,
February 2003-September 2005.
GL-2340
GL-YD
GL-P
Orthophosphate
0.12
0.10
0.08
0.06
0.04
0.02
2003
2004
Sep
Aug
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
Apr
Feb
0.00
2005
Figure 6.8. Greenfield Lake total phosphorus (mg/L) by station,
February 2003-September 2005.
GL-2340
GL-YD
GL-P
0.5
0.4
0.3
0.2
0.1
2003
2004
2005
Sep
Aug
Jul
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
Apr
0
Feb
Total phosphorus
0.6
38
Figure 6.9a. Greenfield Lake chlorophyll a (µ
µ g/L) by station,
February 2003-September 2005.
GL-2340
GL-YD
GL-P
180
160
Chlorophyll a
140
120
100
80
60
40
20
2003
2004
Sep
Aug
July
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
Apr
Feb
0
2005
Figure 6.9b. Greenfield Lake mean chlorophyll a (µ
µ g/L),
February 2003-September 2005.
120
80
60
40
20
2003
2004
2005
Sep
Aug
July
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
Apr
0
Feb
Chlorophyll a
100
39
Figure 6.10a. Greenfield Lake fecal coliform bacterial abundance
(colonies/100mL), February 2003-September 2005.
GL-YD
GL-P
2003
2004
Sep
Aug
July
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
Apr
5,000
4,500
4,000
3,500
3,000
2,500
2,000
1,500
1,000
500
0
Feb
Fecal coliform bacteria
GL-2340
2005
Figure 6.10b. Greenfield Lake mean fecal coliform bacterial
abundance (colonies/100mL), February 2003-September 2005.
1,800
1,400
1,200
1,000
800
600
400
200
2003
2004
2005
Sep
Aug
July
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
May
Mar
Jan
Sep
Aug
Jul
Jun
Apr
0
Feb
Fecal coliform bacteria
1,600
40
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 in 2004. 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 regular monthly 20042005 sampling; two at NB-GLR, three at NWB and four at SB-PGR, and several
additional incidents of hypoxia following a sewage spill (see Section 7.1). 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 slightly lower than 2003-2004, likely a result of
drought and less runoff. The monthly chlorophyll a data (Table 7.1) showed that
Hewletts Creek hosted a major algal bloom at NB-GLR on July 7 (43 µg/L of chlorophyll
a) and additional one of 80 µg/L of chlorophyll a was seen two weeks later; both were
caused by nutrient inputs from a sewage spill (Section 7.1). Station SB-PGR had two
major algal blooms of 133 and 60 µg/L of chlorophyll a and a minor bloom of 30 µg/L of
chlorophyll a following the sewage spill (Section 7.1). Algal blooms have been common
in upper Hewletts Creek in the past (Mallin et al. 1998a; 1999; 2002a; 2004; 2005).
Fecal coliform bacterial counts collected during regular monthly sampling 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; Fig. 7.3; Appendix B). However, sewage
spills in July and September (Section 7.2) severely polluted the creek with fecal bacteria
during this period.
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 (2003-4) study (Mallin et al. 2005). Fecal coliform bacteria counts
exceeded State standards 86% of the time in 2005 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.
41
Table 7.1. Selected water quality parameters at lower and middle creek stations in
Hewletts Creek watershed as mean (standard deviation) / range, August 2004-July
2005. Fecal coliform bacteria presented as geometric mean / range.
_____________________________________________________________________
Parameter
HC-M
HC-2
HC-3
HC-NWB
_____________________________________________________________________
Salinity
(ppt)
33.3 (1.9)
31.4-35.3
33.2 (1.4)
30.8-35.2
30.3 (5.3)
15.2-34.6
23.8 (6.4)
14.0-31.8
Turbidity
(NTU)
4 (3)
1-10
3 (2)
1-7
5 (4)
0-17
7 (3)
3-14
DO
(mg/L)
8.3 (1.9)
5.9-11.7
8.0 (1.8)
5.7-11.7
7.8 (2.0)
5.0-11.7
7.1 (2.6)
4.1-12.0
Nitrate
(mg/L)
0.007 (0.004)
0.003-0.015
0.006 (0.004)
0.002-0.016
0.012 (0.016)
0.003-0.058
Ammonium
(mg/L)
0.018 (0.048)
0.014-0.028
0.019 (0.005)NA
0.014-0.025
Orthophosphate
(mg/L)
0.007 (0.002)
0.004-0.010
0.007 (0.002)
0.004-0.010
Mean N/P
Median
8.5
8.8
8.7
9.1
NA
11.6
7.3
Light attenuation
(K/m)
0.6 (0.1)
0.4-0.7
0.6 (0.2)
0.4-1.1
1.0 (0.6)
0.4-2.3
1.1 (0.6)
0.6-2.0
Chlor a
(µg/L)
1.1 (0.8)
0.2-2.5
1.4 (1.4)
0.2-4.8
2.2 (3.0)
0.2-10.6
7.9 (12.0)
0.3-10.5
0.024 (0.017)
0.005-0.054
0.039 (0.027)
0.011-0.079
0.010 (0.007) 0.012 (0.008)
0.005-0.025 0.006-0.031
Fecal col.
1
2
12
46
CFU/100 mL
0-202
0-158
1-930
5-660
_____________________________________________________________________
NA = not analyzed
42
43
44
Figure 7.3 Geometric mean fecal coliform bacteria counts by
sampling year at selected Hewletts Creek stations.
Fecal coliforms (CFU/100mL)
400
350
300
250
200
150
1993-94
2000-01
2003-04
2004-05
N.C. standard for
human contact water
100
50
0
HC-2
NB-GLR
MB-PGR
SB-PGR
Station
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.
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 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 outflowing stream, sampled at Aster Court.
45
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 2004-July 2005; for PVGC-9, n = 7 months.
_____________________________________________________________________
Parameter
NB-GLR
SB-PGR
MB-PGR
PVGC-9
_____________________________________________________________________
Salinity
(ppt)
11.5 (9.5)
0.2-27.2
16.5 (8.3)
2.9-31.0
0.3 (0.8)
0.1-2.6
0.1 (0.0)
0.1-0.1
Turbidity
(NTU)
7 (5)
1-17
7 (4)
1-13
4 (2)
0-7
2 (1)
1-3
DO
(mg/L)
7.9 (2.4)
4.8-12.3
7.5 (2.6)
4.6-12.6
8.0 (1.6)
5.9-11.7
7.1 (1.7)
5.5-9.7
Nitrate
(mg/L)
0.091 (0.051) 0.043 (0.036)
0.016-0.199 0.005-0.135
0.204 (0.068)
0.113-0.328
0.299 (0.131)
0.070-0.500
Ammonium
(mg/L)
0.029 (0.013) 0.030 (0.015)
0.014-0.062 0.014-0.060
0.057 (0.032)
0.021-0.102
0.046 (0.016)
0.020-0.070
Orthophosphate
(mg/L)
0.018 (0.012) 0.024 (0.035)
0.006-0.044 0.006-0.127
0.019 (0.015)0.011 (0.010)
0.006-0.053
0.005-0.030
Mean N/P ratio
Median
16.0
15.6
12.6
12.0
62.1
57.7
96.3
118.5
Light attenuation
(K/m)
2.4 (2.3)
0.8-6.9
2.3 (1.7)
0.9-5.5
NA
NA
Chlor a
(µg/L)
7.9 (12.0)
0.2-42.7
7.7 (8.7)
0.3-29.5
0.5 (0.2)
0.2-0.9
4.5 (3.5)
1.5-11.7
Fecal coliforms
219
150
159
400
CFU/100 mL
22-4200
23-4150
2-1620
100-1500
_____________________________________________________________________
NA = not analyzed
In 2004 all nutrient species had the highest concentrations at DB-1 and lowest at DB-2
(Table 7.3). There was some reduction of nutrients at DB-4 compared with DB-1,
showing that the property already has some function in water quality improvement. The
exception was nitrate, which had similar concentrations at DB-1 and DB-4. Dissolved
oxygen was low only at DB-1, and turbidity was low at all four sites. Suspended solids
concentrations were periodically elevated at DB-1, but low at the other three sites.
Fecal coliform bacteria counts were highest at DB-1 followed by DB-4 and DB-2 (Table
46
7.3). The data suggest that fecal coliform bacteria and nitrogen should be targeted in
particular 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 2005. n = 7.
_____________________________________________________________________
Parameter
DB-1
DB-2
DB-3
DB-4
_____________________________________________________________________
Turbidity
(NTU)
6 (6)
1-3
2 (1)
1-18
8 (4)
4-15
7 (3)
3-13
TSS
mg/L
16.3 (21.8)
2-63
3.7 (1.7)
2-7
5.9 (2.0)
3-9
4.0 (1.5)
3-7
DO
(mg/L)
5.3 (2.9)
1.7-9.5
6.1 (2.3)
3.8-9.9
6.8 (1.1)
5.8-8.7
7.5 (1.6)
6.2-10.4
Nitrate
(mg/L)
0.085 (0.058) 0.039 (0.020)
0.025-0.170 0.013-0.070
0.066 (0.042)
0.025-0.140
0.084 (0.048)
0.040-0.180
Ammonium
(mg/L)
0.419 (0.347) 0.114 (0.074)
0.040-0.930 0.020-0.250
0.206 (0.031)
0.160-0.250
0.151 (0.040)
0.100-0.200
TN
(mg/L)
1.667 (0.359) 0.809 (0.274)
1.140-2.180 0.370-1.280
0.980 (0.074)0.873 (0.155)
0.870-1.070
0.660-1.070
Orthophosphate
(mg/L)
0.034 (0.020) 0.010 (0.006)
0.005-0.060 0.005-0.060
0.022 (0.018)0.016 (0.013)
0.005-0.050
0.005-0.040
TP
(mg/L)
0.221 (0.196) 0.080 (0.068)
0.080-0.650 0.030-0.230
0.089 (0.027)0.060 (0.022)
0.050-0.120
0.020-0.090
Chlor a
(µg/L)
4.4 (7.9)
0.5-21.9
2.3 (2.2)
0.2-6.3
4.5 (3.9)
0.5-10.0
2.2 (1.9)
0.5-5.6
Fecal coliforms
860
484
220
461
CFU/100 mL
182-2900
100-484
73-550
82-1650
_____________________________________________________________________
47
7.1. The 2005 Major Sewage Spill in Hewletts Creek
Introduction
On Friday, July 1, 2005 the middle branch of Hewletts Creek at Pine Grove Road was
subjected to a raw sewage spill of 3,000,000 gallons. This occurred when a 24-inch
force main coupling repair burst apart. This line carried sewage from Wrightsville
Beach to a pump station on Bradley Creek, then to a pump station (#34) on Hewletts
Creek (near the breach) then on to the Wilmington South Side Wastewater Treatment
plant on River Road (the plant discharge is near Channel Marker 54 in the Cape Fear
River Estuary). This line had been built in the mid 1980s using EPA funds. A citizen
had called the City approximately 6:20 AM with a complaint; city workers were on site at
7:10 AM and found an obvious major leak. The workers turned the pump off but
sewage continued to flow into the creek. During the course of the day they dug down 68 feet to find the problem, finally finishing a temporary repair at 10:30 PM. The workers
estimated that the spill had begun about 5:00 AM; thus the sewage spill occurred over a
near-18 hour period (Hugh Caldwell, City of Wilmington, personal communication).
Some waste flowed into the creek or nearby swamp forest, and some flowed into the
nearest storm drains, which drain directly into Hewletts Creek. Both the North Carolina
Division of Water Quality (DWQ) and the N.C. Shellfish Sanitation Section were alerted
that morning, and as a result the N.C. Division of Marine Fisheries closed the creek and
a large section of the Intracoastal Waterway (ICW) to shellfishing, and Shellfish
Sanitation closed that area to swimming. This section of the ICW encompassed the
area between the Wrightsville Beach Bridge and ICW Channel Marker 141 near Peden
Point, including all tributaries between.
Materials and Methods
During the first day the waste traveled down the creek into the ICW, then across the
ICW and out to the ocean through the Masonboro Channel, according to strong sewage
odors detected by citizens recreating on the ICW and the captain of a UNCW research
vessel passing down the ICW. Regulators from the N.C. DWQ sampled the area on
Saturday, July 2, then again on July 4 and 6. Researchers from the UNCW Aquatic
Ecology Laboratory sampled the water column in the area on July 3, 5, 7, 15, 21, and
on August 8. Researchers from the UNCW Department of Biological Sciences
collected sediment samples for fecal bacteria on July 6, 6, 8, 11, 13, 15, 18, 20, 22, 26,
29, August 2 and August 11. Most water column samples included on-site temperature,
pH, turbidity, salinity/conductivity and dissolved oxygen, fecal coliform bacteria,
ammonium, nitrate, total nitrogen, orthophosphate and total phosphorus, and
chlorophyll a. Sediment samples included fecal coliform bacteria and enterococci.
Stations sampled included MB-PGR (spill site), SB-PGR (south branch at Pine Grove
Rd.), NB-GLR (north branch at Greenville Loop Rd.), HC-M (creek mouth), HC-3 (at a
dock on the north shore of the creek), HC-NWB (the northwest branch of the creek
between HC-3 and the tributary stations), the Masonboro Channel on the ICW south of
the creek mouth, and the Shinn Creek Channel on the ICW north of the creek mouth.
Stations sampled for sediment bacteria include MB-PGR, SB-PGR, NB-GLR and MSDOCK, a control site located near the junction of Hewletts Creek and the ICW.
48
Results and Discussion
Dissolved Oxygen and Fish: The day following the spill N.C. DWQ personnel did not
report any dead fish in the creek or waterway, and creek dissolved oxygen (DO)
concentrations were all at 5.0 mg/L or higher (Table 7.4). A day later, July 3, showed a
much different landscape. While the ICW remained clear, UNCW researchers
sampling by boat began encountering dead fish about halfway up the creek from the
ICW. About 100 were counted in the main channel, including 15 eels, 8 flounder,
mullet and numerous small fish. There were many decomposing gobs of flesh, with
birds and crabs feeding on them (dissolved oxygen was 1.9 mg/L). The researchers
then proceeded by truck to NB-GLR where about 200 dead fish were counted (DO 4.4
mg/L); then on to SB-PGR, where about 140 dead fish were counted, and many more
seen floating upstream. There was a strong sewage odor present, and DO was 2.4
mg/L. The sewage had obviously been carried downstream from MB-GLR toward the
ICW, then much of it was sloshed back upstream into the north and south branches,
where the BOD load from the sewage caused a decrease in DO. Many fish were
trapped by the rising tide in hypoxic waters and died along the marsh edge. The high
water temperatures (25-28ºC) led to rapid decomposition of the fish, contributing
additional BOD to the sewage BOD load. The dead fish decomposed or were
consumed by scavengers over the next two days; however, hypoxic water < 3.0 mg/L
DO were present on July 4 and waters with DO < 4.0 mg/L were encountered on July 5.
From July 6 on all water sampled had DO values of 4.0 mg/L or higher (Table 7.4).
Animal mortality was not confined to fish, however. On July 7 UNCW researchers
photographed several ducks along the shore of the creek that were obviously sick and
dying.
Table 7.4. Water column dissolved oxygen concentrations by date and station following
the July 1, 2005 Hewlett’s creek sewage spill (as mg/L).
_____________________________________________________________________
Station
7/2
7/3
7/4
7/6
7/7
7/15
7/21
8/8
_____________________________________________________________________
HC-M
5.5
7.7
NA
5.4
6.6
5.0
4.9
6.0
HC-3
5.0
3.5
5.7
5.1
6.3
6.3
4.0
5.5
HC-NWB
NA
1.9
NA
NA
4.1
NA
NA
NA
SB-PGR
NA
2.4
2.5
6.3
4.8
9.6
4.0
4.6
MB-PGR
NA
7.6
NA
NA
7.0
6.1
6.1
6.5
NB-GLR
NA
7.7
2.8
6.7
6.5
6.5
6.5
4.2
_____________________________________________________________________
NA = not analyzed
Fecal Bacteria: On July 2 fecal coliform counts were high; at HC-3 they were 270,000
CFU/100 mL, and in the creek mouth they ranged from 2,000 to 3,200 CFU/100 mL
(Table 7.5). However, counts were all below 100 CFU/100 mL in the ICW. Fecal
coliform bacteria counts in the water column of the creek were high (15,000-21,000
CFU/mL) on July 3, and then decreased to 2,000 CFU/100 mL in the channel on July 4.
After July 4 main channel fecal coliform bacteria counts generally stayed below 100
CFU/100 mL. In contrast the tributaries (SB-PGR and NB-GLR) had counts
49
approximately 3,000 CFU/100 mL until July 6, then a brief decrease, then an increase
again on July 15 to 2,900 CFU/100 mL following a rain event (Table 7.5). From then on
tributary fecal coliform counts decreased to normal levels. In the main channel during
the first few days, loss of fecal coliforms from the water column followed a roughly
logarithmic decrease. Loss of fecal coliforms from the water column can occur from
predation by protozoans, mortality from sunlight (UV radiation), dilution by incoming
tides and sedimentation. As will be seen in the following section, sedimentation of fecal
bacteria was a critically important issue following this sewage spill.
Table 7.5. Water column fecal coliform bacteria counts by date and station following the
July 1, 2005 Hewletts creek sewage spill (as CFU/100 mL).
_____________________________________________________________________
Station
7/2
7/3
7/4
7/6
7/7
7/15
7/21
8/8
_____________________________________________________________________
HC-M
3,200
176
NA
1
9
5
46
1
HC-3
270,000 21,000
220
69
21
24
96
2
HC-NWB
NA
15,800
NA
NA
242
NA
NA
NA
SB-PGR
NA
NA
3,000
358
211
312
362
30
MB-PGR
NA
2,100
780
NA
224
900
291
128
NB-GLR
NA
NA
NA
3,200
546
2,900
655
180
_____________________________________________________________________
NA – not analyzed
Post-spill sediment bacteria sampling was initiated by Dr. Larry Cahoon’s laboratory on
July 6. Reference samples were available for Hewletts Creek as a WRRI-sponsored
project regarding sediment fecal bacteria had been ongoing since 2004. Results (Table
7.6) showed that post spill samples were an order of magnitude higher than pre-spill
counts. Counts appeared to decrease after a few days, but the rain event (noted
above) caused high sediment counts again (7/15). Sampling was continued until early
August. The latter dates showed a general decrease to background levels, with high
counts periodically occurring. The fecal bacteria in the sediments form a reservoir of
viable fecal microbes that is available to enter the water column following a
mixing/stirring event such as a rainstorm or people or pets wading or otherwise
disturbing the sediments. As an on-site test, on 7/7 researchers for the Aquatic Ecology
Laboratory collected a fecal coliform sample from the water at HC-3, and then
proceeded to pass the motor over the site, stirring the water and sediments below.
Counts taken from before the stirring were 21 CFU/100 mL while counts taken after the
stirring were nearly three times greater, 60 CFU/100 mL. The presence and
persistence of the sediment fecal bacteria demonstrate that water column sampling of
fecal bacteria is insufficient when analyzing an area for human contact safety after a
pollution event; sediment sampling also produces necessary data.
50
Table 7.6. Sediment fecal coliform bacteria counts by date and station following the July
2
1, 2005 Hewletts Creek sewage spill (as CFU/cm ). Samples collected 10/31/04 and
1/28/05 are shown as control (non-spill) counts for comparison.
_____________________________________________________________________
Station
10/31/04 1/28/05 7/6
7/11
7/15
7/22
8/2
8/11
_____________________________________________________________________
MS-DOCK
NA
NA
0
0
23
0
0
11
SB-PGR
488
358
2743
526
5335
396
732
1886
MB-PGR
NA
NA
5106
1151
1448
777
457
80
NB-GLR
53
579
3506
442
991
663
1315
914
_____________________________________________________________________
NA = not analyzed
Nutrients and Algal Blooms: Nutrient concentrations in the raw sewage were high (TKN
= 40.2 mg/L; ammonium = 23.3 mg/L, total phosphorus = 5.3 mg/L - Dolores Bradshaw,
City of Wilmington, personnel communication). Upon reaching the creek, nutrient
concentrations apparently decreased at a surprisingly fast rate. Even on July 2 TKN
levels were < 2.0 mg/L, ammonium < 1.0 mg/L, nitrate < 0.3 mg/L and TP was < 0.06
mg/L. By July 5 TKN decreased to < 0.7 mg/L and no unusual pulses of that or other
nutrient species were encountered. Some of the nutrients were taken up by
phytoplankton; blooms were recorded at NB-GLR on July 7 and July 21 of 43 and 80
µg/l chlorophyll a, respectively, and blooms of 30, 133 and 60 µg/L chlorophyll a were
recorded at SB-PGR on July 7, July 15 and July 21, respectively. One of the blooms
(7/15) was analyzed by microscopy. At SB-PGR the bloom was dominated by
cryptomonads, primarily Chroomonas amphioxiae. AT NB-GLR the flora was a mixture
of Nitzschia closterium, small naviculoid diatoms, cryptomonads, the euglenoid
Eutreptia sp. and the dinoflagellate Gymnodinium sp. In addition to the phytoplankton,
clearly, the salt marsh must have absorbed a large amount of the nutrient load from the
sewage into the soils (and probably removed some via microbial denitrification), and
some was taken up by Spartina, Juncus and other macrophytes, and the periphyton.
Additional Comments Related to the Spill: Regulatory authorities lifted the ban on
swimming in the ICW after a two-week period. However, due to the persistence of the
fecal bacteria in the sediments and the increases noted after rain events, the ban on
swimming in Hewletts Creek remained in effect for the remainder of the summer of
2005. Coincidentally, several individuals who were swimming or otherwise recreating in
the ICW during the Fourth of July weekend came down with infections. The City made
permanent repairs on the break Tuesday August 9 with a heavy-duty coupler made of
cast iron. As an additional complimentary measure a low flow alarm was installed at
Southside Wastewater Treatment Plant to detect low flow from the pump station on
Hewlett’s Creek. The City was fined $50,000 by the North Carolina Division of Water
Quality as a result of the spill.
That was not the only pollution incident to affect Hewletts Creek in 2005, however.
Another sewage spill occurred in the Hewletts Creek watershed September 15 when a
24-inch line ruptured and spilled an unknown volume of sewage onto Shipyard Drive
and ditches and yards along Pine Valley Drive. Some of the waste entered storm
drains, and from there entered Hewletts Creek. Repairs were completed the next
51
morning. Samples collected in Hewletts Creek by the UNCW Aquatic Ecology
Laboratory found elevated fecal coliform bacteria counts in the upper tributary stations
(PVGC-9 – 2487 CFU/100 mL; MB-PGR – 2790 CFU/100 ML; SB-PGR – 2195
CFU/100 mL; NB-GLR – 840 CFU/100 mL). Station MB-PGR is located downstream
from PVGC-9 (Fig. 7.1). Subsequent sampling on September 19 showed a
considerable water-column decrease in fecal coliform bacteria (PVGC9 – 380 CFU/100
mL; MB-PGR – 700 CFU/100 mL; SB-PGR – 160 CFU/100 mL; NB-GLR – 400
CFU/100 mL) to levels commonly found at these locations (Table 7.2), although the
main channel sites were still elevated (HC-3 – 60 CFU/100 mL; HC-2 – 100 CFU/100
mL).
The July 1 sewage spill demonstrated two important points. First, following a major
pollution incident where human or animal waste is involved, sampling the water column
for fecal bacteria is not sufficient to obtain a complete picture of the system in terms of
human health issues. Large quantities of the polluting bacteria settled to the sediments
and remained viable for several weeks, and were clearly subject to resuspension in the
water column after a mixing event. This has been demonstrated previously following a
large swine waste lagoon spill that entered the New River (Burkholder et al. 1997).
There, significant quantities of fecal bacteria remained in the sediments for nearly three
months after the spill. Fecal bacteria on or in the sediments are largely protected from
UV radiation, a principal means of death or deactivation in the water column. Also, the
sediments contain carbon, nitrogen, and phosphorus, which are key nutrients for
bacterial survival and growth. We recommend that regulatory authorities devise
sampling and assessment plans for pollution incidents that consider sedimentassociated fecal bacteria.
A second point of interest is the function of the salt marsh as a nutrient removal
mechanism. Raw sewage has very high nutrient concentrations, yet the nutrients
rapidly disappeared from the water column. While post-spill phytoplankton blooms
indicated some nutrient uptake by these primary producers, it is likely that additional
uptake occurred into benthic and epiphytic microalgae (periphyton) and salt marsh
macrophytes, such as Spartina. Microbial denitrification also likely removed nitrogen
from the system. Thus, the spill demonstrated the important role salt marshes play in
removal of nutrient pollution.
Reference Cited
Burkholder, J.M., M.A. Mallin, H.B. Glasgow, Jr., L.M. Larsen, M.R. McIver, G.C. Shank,
N. Deamer-Melia, D.S. Briley, J. Springer, B.W. Touchettte and E. K. Hannon. 1997.
Impacts to a coastal river and estuary from rupture of a swine waste holding lagoon.
Journal of Environmental Quality 26:1451-1466.
52
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 did not exceed North
Carolina water quality standards at any of the other stations (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
decrease over levels in 2003-2004, especially at the uppermost stations (Mallin et al.
2004), probably a reflection of lower rainfall and runoff. 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 minor
algal bloom of 38 µg/L as chlorophyll a at HW-DT. 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). Light
attenuation showed generally clear water except for an elevated reading of 3.4/m at
HW-DT in June.
Table 8.1. Water quality summary statistics for Howe Creek, August 2004-July 2005,
as mean (st. dev.) / range. Fecal coliform bacteria as geometric mean / range.
Salinity
Diss. oxygen Turbidity Light
Chlor a Fecal coliforms
(ppt)
(mg/L)
(NTU)
(K/m)
(µg/L)
(CFU/100 mL)
_____________________________________________________________________
HW-M
33.3 (1.9)
28.7-35.1
7.5 (1.7)
5.1-9.8
3 (2)
0-8
0.7 (0.2)
0.4-1.0
1.2 (0.9)
0.2-2.6
1
0-38
HW-FP
32.9 (2.3)
27.9-35.0
7.5 (1.7)
4.9-9.9
3 (2)
0-7
0.6 (0.3)
0.3-1.2
1.2 (1.1)
0.2-3.0
1
0-80
HW-GC
29.0 (5.7)
18.0-34.1
7.2 (1.8)
4.2-9.8
4 (3)
1-11
1.3 (1.1)
0.5-3.7
1.4 (1.2)
0.2-3.3
9
1-106
HW-GP
14.4 (11.8)
1.6-31.3
7.2 (1.8)
4.5-9.8
6 (4)
0-12
2.0 (0.7)
0.7-2.7
5.7 (5.3)
0.3-14.7
72
8-355
HW-DT
3.7 (4.6)
0.2-11.9
8.3 (1.7)
5.7-11.0
10 (4)
2-15
2.4 (0.7)
1.5-3.4
9.5 (10.5)
0.6-38.3
265
65-780
Figure 8.1. Howe Creek watershed and sampling sites.
53
54
Figure 8.2. Chlorophyll a concentrations (algal blooms) in
Howe Creek below Graham Pond before and after 1998 wetland
enhancement in upper Graham Pond.
100
wetland
enhancement
Chlorophyll a (ppb)
90
80
70
NC chlorophyll a standard for impaired waters
60
50
40
30
20
10
A
ug
Fe us
br t
ua
A ry
ug
Fe us
br t
ua
A ry
ug
Fe us
br t
ua
A ry
ug
Fe us
br t
ua
A ry
ug
Fe us
br t
ua
A ry
ug
Fe us
br t
ua
A ry
ug
Fe us
br t
ua
A ry
ug
Fe us
br t
ua
A ry
ug
Fe us
br t
ua
A ry
ug
Fe us
br t
ua
A ry
ug
Fe us
br t
ua
A ry
ug
Fe us
br t
ua
ry
0
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
Table 8.2. Nutrient concentration summary statistics for Howe Creek, August 2004-July
2005, as mean (standard deviation) / range, N/P ratio as mean / median.
_____________________________________________________________________
Nitrate
Ammonium
Orthophosphate
Molar
(mg/L)
(mg/L)
(mg/L)
N/P ratio
_____________________________________________________________________
HW-M
HW-FP
0.007 (0.005)0.027 (0.016)0.008 (0.002)
9.8
0.003-0.015
0.014-0.062
0.006-0.012
7.6
0.008 (0.005)0.024 (0.011)0.008 (0.002)
8.4
0.002-0.017
0.014-0.045
0.005-0.014
8.8
HW-GC
0.010 (0.008)
0.001-0.032
HW-GP
0.012 (0.011)0.023 (0.011)0.014 (0.008)
6.1
0.001-0.035
0.014-0.045
0.006-0.030
HW-DT
NA
0.009 (0.003)
0.005-0.015
NA
5.9
0.033 (0.026)0.032 (0.023)0.010 (0.003)14.6
0.002-0.077
0.014-0.084
0.006-0.017
9.6
____________________________________________________________________
NA = not analyzed
55
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). HWGP exceeded the North Carolina human contact standard on two of 12 occasions, and
HW-DT exceeded the standard on seven of 12 occasions (Appendix B). The 20042005 data show an improvement in fecal coliform counts after a sharp decrease in
bacterial water quality seen in 2003-2004 Howe Creek (Fig. 8.3). Station HW-GP in
particular showed improvement. Since a previous analysis associated with the opening
of Mason’s Inlet (Mallin et al. 2003) showed that fecal coliform counts in the uppermost
stations were strongly correlated with rainfall, the drought of 2005 may be responsible
for the lowered counts.
Figure 8.3. Geometric mean fecal coliform bacteria counts for
Howe Creek over time, 1993 - 2005
FECAL COLIFORMS (CFU/100
mL)
600
500
400
300
NC fecal coliform standard for human contact
200
100
0
HW-M
creek mouth area
HW-FP
HW-GC
HW-GP
HW-DT
station farthest upstream
STATION
1993-1994
1996-1997
1999-2000
2002-2003
2003-2004
2004-2005
2001-2002
56
9.0 Motts Creek
Motts Creek drains into the Cape Fear River Estuary (Fig. 9.1), and the creek area 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 occurred along Carolina Beach Road near its
junction with Highway 421.
Dissolved oxygen concentrations were below 4.5 mg/L from May through September
(range 2.8-4.4 mg/L) similar to previous years (Mallin et al. 2003; 2004). Unlike
previous years, neither turbidity nor suspended solids were problematic in 2005,
possibly a result of low rainfall. Fecal coliform contamination was a problem in Motts
Creek, with the geometric mean of 353 CFU/100 mL exceeding the State standard of
200 CFU/100 mL, and samples exceeding this standard on six of seven occasions
(Appendix B). Fecal coliform contamination increased over that of previous years.
Total nitrogen, ammonium, and total phosphorus levels were similar to the previous
year’s study, but chlorophyll a concentrations generally decreased, with no algal blooms
detected in 2005 (Table 9.1). BOD5 was sampled on seven occasions in 2005, yielding
a mean value of 1.3 mg/L and a median value of 1.2 mg/L, generally lower than the
previous years (Mallin et al. 2003; 2004; 2005). Thus, this creek showed mixed water
quality, with algal blooms and BOD decreasing, and dissolved oxygen and fecal
coliform counts somewhat poorer compared with last year.
57
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 2005. Fecal coliforms as geometric mean / range.
_____________________________________________________________________
Parameter
MOT-RR
Mean (SD)
Range
_____________________________________________________________________
Salinity (ppt)
0.3 (0.3)
0.2-0.9
TSS (mg/L)
7.9 (3.2)
10.0-32.0
Turbidity (NTU)
10 (4)
4-15
DO (mg/L)
4.9 (2.4)
2.8-9.7
Nitrate (mg/L)
0.107 (0.048)
0.060-0.190
Ammonium (mg/L)
0.057 (0.046)
0.030-0.150
Total nitrogen (mg/L)
0.966 (0.266)0.640-1.470
Orthophosphate (mg/L)
0.007 (0.004)0.002-0.013
Total phosphorus (mg/L)
0.060 (0.016)0.040-0.090
Mean N/P ratio
Median
85.2
55.1
Chlor a (µg/L)
4.2 (3.2)
0.6-8.7
BOD5 (mg/L)
1.3 (0.6)
0.8-2.7
BOD20
5.0 (1.5)
3.9-7.9
Fecal coliforms (CFU/100 mL)
353
45-900
_____________________________________________________________________
58
59
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 2004 and 2005, three at the station draining upper Bayshore Drive
(Appendix B). Fecal coliform bacteria were not sampled at this creek during the past
year. Nitrate and orthophosphate concentrations were similar to the previous year, and
phytoplankton biomass as chlorophyll a was low with only one minor algal bloom of 23
µg/L noted at PC-BDUS (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 creeks in New Hanover County.
Table 10.1. Selected water quality parameters in Pages Creek as mean (standard
deviation) / range, August 2004-July 2005.
_____________________________________________________________________
Parameter
PC-M
PC-BDDS
PC-BDUS
_____________________________________________________________________
Salinity (ppt)
33.9 (1.2)
31.8-35.5
28.4 (9.0)
3.3-33.8
12.1 (8.6)
1.6-24.0
Turbidity (NTU)
4 (4)
0-11
5 (3)
1-10
5 (2)
2-8
DO (mg/L)
7.8 (1.7)
5.2-10.2
7.0 (2.0)
3.9-10.0
6.8 (1.5)
4.6-8.9
Nitrate (mg/L)
0.007(0.002)
0.005-0.010
0.036(0.043)
0.007-0.156
0.026(0.014)
0.011-0.060
Ammonium (mg/L)
0.017(0.005) 0.037(0.047) 0.051(0.030)
0.014-0.029
0.014-0.166
0.014-0.114
Orthophosphate (mg/L)
0.007(0.002)
0.005-0.010
Mean N/P Ratio
median
7.6
7.6
Chlor a (µg/L)
0.013(0.004)
0.004-0.023
9.9
6.0
0.016(0.005)
0.007-0.025
11.3
8.0
1.4 (1.4)
2.1 (2.1)
5.6 (7.3)
0.2-4.1
0.3-7.1
0.3-22.8
_____________________________________________________________________
60
Figure 10.1. Pages Creek watershed and sampling sites.
61
11.0 Smith Creek
Smith Creek drains into the lower Northeast Cape Fear River just before it joins with the
mainstem Cape Fear River at Wilmington (Fig. 11.1). Two estuarine sites on Smith
Creek proper, SC-23 and SC-CH (Fig. 11.1) were sampled in 2005. Dissolved oxygen
concentrations were below 5.0 mg/L on three occasions at SC-23 and on four
occasions at SC-CH between June and September 2005. 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 not exceeded during
2005, an improvement over 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 2005. However, lesser algal
blooms of 35 µg/L and 25 µg/L occurred at SC-23 and SC-CH, respectively, in August,
and a bloom of 25 µg/L occurred at SC-23 in July. Fecal coliform bacteria
concentrations were above 200 CFU/100 mL on only one occasion (at SC-CH), an
improvement over the past two years (Mallin et al. 2004; 2005) 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 2005 at SC-CH, with a
mean value of 1.4 mg/L and a median value of 1.5 mg/L, similar to last year.
62
Table 11.1. Selected water quality parameters in Smith Creek watershed as mean
(standard deviation) / range. January - September 2005.
_____________________________________________________________________
Parameter
SC-23
SC-CH
Mean (SD) Range
Mean (SD) Range
_____________________________________________________________________
Salinity (ppt)
2.3 (3.6)
0.0-15.7
0.2 (0.1)
0.1-0.3
Dissolved oxygen (mg/L)
6.1 (2.4)
3.2-9.6
5.8 (2.7)
3.1-10.2
Turbidity (NTU)
10 (5)
5-16
13 (6)
7-25
TSS (mg/L)
10.3 (4.7)
5.0-19.0
16.1 (5.8)
7.0-22.0
Nitrate (mg/L)
0.070 (0.035) 0.030-0.130
0.169 (0.101) 0.050-0.320
Ammonium (mg/L)
0.037 (0.015) 0.010-0.050
0.063 (0.023) 0.040-0.110
Total nitrogen (mg/L)
0.802 (0.283) 0.400-1.100
1.127 (0.208) 0.840-1.440
Orthophosphate (mg/L)
0.008 (0.004) 0.005-0.013
0.013 (0.010) 0.005-0.030
Total phosphorus (mg/L)
0.072 (0.028) 0.050-0.120
0.097 (0.039) 0.070-0.180
Mean N/P ratio
Median
43.2
48.7
57.4
61.4
Chlor. a (µg/L)
14.1 (12.1)
1.5-34.7
9.0 (9.7)
0.9-24.9
Fecal col. /100 mL
(geomean / range)
53
9-290
65
18-173
BOD5 (mg/L)
NA
NA
1.4 (0.3)
1.0-1.8
BOD20 (mg/L)
NA
NA
5.5 (1.2)
3.8-7.1
_____________________________________________________________________
NA = not analyzed
63
64
12.0 Whiskey Creek
Whiskey Creek drains into the ICW. Sampling of this creek began in August 1999.
Five stations were sampled in 2004-2005; 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 only
one of 12 occasions each at WC-MLR and WC-AB in 2004-2005 (Table 12.1).
Turbidity was within state standards for tidal waters on all sampling occasions (Table
12.1; Appendix B). There was one minor algal bloom of 18 µg/L at WC-MLR in June
2005; chlorophyll a concentrations are usually low in this creek (Table 12.1). Nitrate
concentrations were highest upstream at WC-NB, followed by WC-SB (Table 12.2),
similar to previous years. Nitrate was slightly lower than 2003-2004, likely as result of
less runoff from drought conditions. 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 similar among all stations except for WC-SB.
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 20042005. 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 2004-July
2005, presented as mean (standard deviation) / range.
Salinity
Dissolved oxygen Turbidity
Chlor a Light attenuation
(ppt)
(mg/L)
(NTU)
(µg/L)
(k/m)
_____________________________________________________________________
WC-MB
30.4 (2.1)
26.3-33.6
7.6 (2.0)
5.0-10.8
3 (2)
0-9
3.1 (2.2)
0.3-7.2
1.0 (0.3)
0.7-1.6
WC-AB
27.7 (3.0)
21.7-32.5
7.6 (2.4)
4.6-11.6
6 (3)
2-11
2.8 (2.3)
0.2-8.4
NA
NA
WC-MLR
23.0 (4.2)
16.6-31.7
7.5 (2.6)
3.9-12.5
7 (5)
2-20
4.3 (4.9)
0.3-18.1
NA
NA
WC-SB
0.1 (0.0)
0.0-0.1
7.2 (0.8)
6.2-9.0
6 (4)
2-15
0.8 (0.6)
0.1-1.7
NA
NA
WC-NB
0.1 (0.1)
7.3 (1.2)
4 (2)
0.3 (0.2)
NA
0.1-0.2
5.1-10.2
2-7
0.0-0.8
NA
_____________________________________________________________________
NA = not analyzed
65
Table 12.2. Nutrient concentration summary statistics for Whiskey Creek, August 2004July 2005, as mean (standard deviation) / range, N/P ratio as mean / median.
_____________________________________________________________________
Nitrate
Ammonium
Phosphate Molar N/P ratio
(mg/L)
(mg/L)
(mg/L)
_____________________________________________________________________
WC-MB
0.021 (0.020)0.023 (0.011)0.010 (0.003)
9.4
0.006-0.065
0.014-0.044
0.006-0.015
WC-AB
0.024 (0.019)
0.005-0.069
WC-MLR
0.030 (0.023)0.044 (0.033)0.012 (0.005)
12.4
0.010-0.075
0.014-0.108
0.006-0.023
13.2
0.057 (0.012)0.156 (0.102)0.002 (0.001)
658.9
0.041-0.082
0.057-0.396
0.001-0.004
265.8
WC-SB
WC-NB
NA
0.011 (0.004)
0.007-0.021
8.7
NA
0.161 (0.061)0.136 (0.075)0.012 (0.009)
92.3
0.094-0.265
0.052-0.326
0.003-0.031
64.9
_____________________________________________________________________
NA = not analyzed
66
Figure 12.1. Whiskey Creek. Watershed and sampling sites.
67
13.0 Fecal contamination of tidal creek sediments: Factors controlling indicator
bacteria concentrations
Byron R. Toothman, Michelle L. Ortwine, Lawrence B. Cahoon
1
Department of Biology and Marine Biology
UNC Wilmington
1910-962-3706, Cahoon@uncw.edu
Abstract
A study was performed to determine the abundance of fecal bacteria in Bradley Creek
sediments and to see if their concentrations were related to sediment phosphorus (P),
sediment carbon (C), salinity and water temperature. The concentrations of fecal
indicator bacteria in sediments of Bradley Creek were highly variable, spanning over 3
orders of magnitude. Fecal coliform concentrations had a geometric mean of 179 CFU
cm-2 (std. dev. = 411, range = 0 – 3,230) in a total of 154 samples. This geometric
mean value corresponds to a value of 179 CFU/100 mls if all these bacteria were
suspended in a water column 1 meter deep, a value just below that required to close
the water to human body contact (200 CFU/100 ml). The regulatory standard for
shellfishing is much lower, 14 CFU/100 ml; 113 of the 154 samples exceeded this value
using analogous assumptions. Fecal enterococcus concentrations had a geometric
mean value of 285 CFU cm-2 (std. dev. = 433, range = 0-1726). This geometric mean
value corresponds to a value of 285 CFU per 100 ml if all these bacteria were
suspended in a water column 1 meter deep, a value well above that required to close
the water to human body contact (33 CFU/100 ml). Thus, the levels of fecal indicator
bacteria measured in Bradley Creek’s sediments frequently represent serious potential
problems for human uses of these waters.
Sediment fecal coliform bacteria were negatively correlated with salinity and positively
correlated with water temperature, but enterococcus had no significant relationship to
these factors. Rainfall in the 24 hour period preceding sampling was also significantly
related to fecal coliform counts. Laboratory experiments showed that both fecal
coliform bacteria and enterococcus bacteria counts were positively related to increasing
concentrations of usable (or bioavailable) carbon (dextrose). However, only
enterococcus was significantly correlated to sediment P concentrations, and only when
background P concentrations were low. Bioavailable C is abundant in stormwater
runoff. Because of this, and the fact that sediment fecal bacteria counts were positively
related to rainfall, we conclude that storm water runoff is the most significant factor
driving sediment contamination.
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
68
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). Our earlier data from
6
-2
the Bradley Creek drainage showed fecal coliform levels on the order of 10 CFU m of
sediment (Cahoon et al., 2005). 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 sedimentassociated 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).
Major sewage spills in the Hewletts Creek drainage during 2005 drove significant
increases in the concentrations of fecal indicator bacteria in creek sediments (see
discussion elsewhere in this report). Rain events shortly after these spills also caused
increases in sediment concentrations of fecal indicator bacteria, illustrating the
importance of storm water runoff as a source mechanism for this contamination.
However, fecal bacteria contamination even weeks after storm events or spills argue for
persistence of these bacteria in tidal creek ecosystems. In addition, variation in bacteria
concentrations among sampling times and locations suggests that factors other than
variable recruitment control bacterial concentrations in sediments. Therefore, we
investigated the effects of the macronutrients phosphorus and bio-available carbon as
factors controlling growth of sediment populations of fecal indicator bacteria.
We measured the concentrations of two kinds of fecal indicator bacteria, fecal coliforms
and fecal enterococcus, in sediments, as regulators have established standards for
these two groups in estuarine ecosystems. We concurrently measured temperature,
salinity, and the concentrations of sediment phosphorus and total carbohydrate for
comparison to bacterial concentrations. We also compared responses of sediment
bacteria populations to rainfall history. Finally, we conducted experiments that
examined responses of sediment fecal indicator bacteria to combinations of added
phosphorus and bio-available carbon.
Methods
Field Sampling: Sampling sites were located in the Bradley Creek drainage, using
locations previously sampled so as to maintain continuity (Fig. 1). These locations were
sampled at least monthly for sediment phosphorus, sediment fecal coliforms 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 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 phosphatebuffered 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
69
bacteria, method 9222 (APHA, 2001). 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). Similar methods
were used to estimate fecal enterococci following method 9230 C.3.a (APHA, 2001).
Bacterial colonies satisfying the respective criteria for each method were counted after
incubations using either the naked eye, or for plates with numerous colonies, an
Olympus SZ-III stereomicroscope. Counts from each 10ml sample from each of the
three cores from each site were averaged and expressed as the number of colony
-2
forming units per square centimeter (CFU cm ) + one std. dev.
Sediment phosphate was analyzed on a second triplicate set of sediment cores taken
randomly at each sampling site simultaneously with fecal bacteria samples. Sediment
o
cores destined for chemical analyses were iced immediately, frozen initially at -20 C,
o
then stored at -85 C for 24 hours prior to lyophilization using a Virtis Benchtop 3.3
Vacu-Freeze lyophilizer. Lyophilized sediment samples were homogenized and stored
in sealed containers at room temperature prior to sub-sampling for chemical analyses.
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 labile forms of phosphorus to orthophosphate, and likely represents
bio-available phosphorus in sediments, in contrast to more robust extraction and
digestion methods that quantify additional phosphorus that may be less bio-available.
Sediment phosphate content was expressed as ug P (g sediment)-1.
The carbohydrate content of sediment samples was analyzed by the phenol-sulfuric
acid method of Underwood et al. (1995). Approximately 0.2-0.5 g of lyophilized,
homogenized sediment was suspended in 1.0 ml of distilled water, to which 1 ml of 5%
aqueous phenol solution and 5 ml of concentrated sulfuric acid were added while
stirring vigorously. Resulting absorbance was measured at 485 nm on a Milton-Roy
Spectronic 401 spectrophotometer in a 1 cm cuvet against a reagent blank. Standard
curves were established using a dilution series of dextrose (C6H12O6) and total
carbohydrate contents were expressed as µg C (g sediment)-1. The average of three
replicate values from each sample site was calculated along with standard deviation.
70
Figure 1. Map showing sampling locations (and corresponding Tidal Creeks Program
site designations) in the Bradley Creek watershed, named for nearby streets or
tributaries. A=Andover (BC-SBU), BWP=Bluthenthal Wildflower Preserve, CR=Clear
Run (BC-CA), CRT=Clear Run Branch Tributary, E=Eastwood (BC-NBU), M=Mallard
(BC-CR), REC=Recreation Center Pond, S=Softwind (BC-SB), W=Wrightsville (BCNB).
________________________________________________________________
Experimental Protocols: Sediment cores were collected as above at sampling
locations in the Bradley Creek watershed (Fig. 1) and one other location (“210”, at the
point where Prince George’s Creek crosses NC Hwy 210) for experimental
determinations of responses of fecal indicator bacteria to added P and organic carbon.
A randomly selected triplicate set of sediment cores was analyzed for initial
concentrations of fecal coliform and fecal enterococcus bacteria as above. Four
treatments were used in a 2 x 2 design, executed in triplicate: 3 sediment cores were
incubated with 1 liter of incubation medium (0.4% NaCl buffered to pH 8.0 with sodium
borate) +100 µg P/liter (as KH2PO4), 3 sediment cores were incubated with 1 liter of
incubation medium + 1000 µg dextrose C/liter, 3 sediment cores were incubated with 1
liter of incubation medium + 100 µg P/liter + 1000 ug dextrose C/liter, and 3 sediment
cores were incubated with 1 liter of incubation medium only. Incubations lasted 24
71
o
hours at 37 C, after which sediment cores were processed for analyses of fecal
coliform and fecal enterococcus bacteria as above.
Statistical Analyses: All statistical analyses were performed on SAS Institute’s JMP
version 4.0, except as noted. Data sets were examined for normality using the ShapiroWilk test. Non-normal data sets were transformed as appropriate; bacteria
concentration data were typically log-transformed (Log[counts+1]). When
transformation could not yield a normal distribution, non-parametric statistical tests were
used to analyze original data. The effects of sediment P, carbohydrate, and other
variables on bacterial concentrations were analyzed by linear regression and multiple
linear regressions. Results of experimental incubations employing a 2 x 2 design were
log-transformed and analyzed by 2-way ANOVA (Sokal and Rohlf, 1995); pooled
experimental results were analyzed by a Kruskal-Wallis test.
Results
The concentrations of fecal indicator bacteria in sediments of Bradley Creek were highly
variable, spanning over 3 orders of magnitude. Fecal coliform concentrations had a
2
geometric mean of 179 CFU/ cm (std. dev. = 411, range = 0 – 3,230) in a total of 154
samples (sites x times) collected between January, 2003 and March, 2005. This
geometric mean value corresponds to a value of 179 CFU/100 mls if all these bacteria
were suspended in a water column 1 meter deep, a value just below that required to
close the water to human body contact (200 CFU/100 ml). The regulatory standard for
shellfishing is much lower, 14 CFU/100 mls; 113 of the 154 samples exceeded this
value using analogous assumptions. Mean values for the respective sampling sites
were highly variable (Table 1), but all sites had at least one value exceeding 200 CFU
cm-2. Fecal enterococcus concentrations had a geometric mean value of 285 CFU cm-2
(std. dev. = 433, range = 0-1726) in a total of 45 samples (sites x times) collected
between July, 2004 and March, 2005. This geometric mean value corresponds to a
value of 285 CFU per 100 mls if all these bacteria were suspended in a water column 1
meter deep, a value well above that required to close the water to human body contact
(33 CFU/100 ml). Thus, the levels of fecal indicator bacteria measured in Bradley
Creek’s sediments frequently represent serious potential problems for human uses of
these waters.
Table 1. Concentrations of fecal indicator bacteria in sediments at sampling sites within
the Bradley Creek drainage, CFU/cm2. Fecal coliforms= FC, fecal enterococcus = FE.
site designations as in Fig. 1.
Site
A
CR
E
M
S
W_
FC Mean 340
33
186
257
125
132
Std. Dev. 697
69
274
550
301
152
FE Mean 332
203
365
65
251
528
Std. Dev. 587
294
494
90
448
732
Analysis of correlations between fecal indicator bacteria concentrations and other
parameters revealed mostly non-significant relationships. Neither fecal coliform nor
72
fecal enterococcus concentrations in sediments were related to sediment phosphorus
concentration, sediment carbohydrate content, or rainfall in the 24 or 48 hour periods
prior to sampling (Table 2). There was a significant relationship between salinity and
fecal coliform concentration in sediments (Fig. 2), but not between salinity and fecal
enterococcus concentrations in sediments (Table 2), and between temperature and
sediment fecal coliform concentrations (Fig. 3) but not between temperature and fecal
enterococcus concentrations in sediments (Table 2). However, both significant
2
relationships had very low correlation coefficients (r values), indicating poor
explanatory power.
Table 2. Results of regression analyses between sediment fecal indicator bacteria
2
concentrations (log[CFU/cm ]) and environmental parameters. Significant effects in
bold.
Parameter
Salinity
Temperature
Sediment P
Sed. Carbohydrate
24 hr Rainfall
48 hr Rainfall
Coliforms
2
F
r
df
-0.04 6.77
0.05 7.9
3x10-7 0.00
0.02 2.38
0.006 0.86
0.001 0.21
1,150
1,150
1,151
1,139
1,147
1,147
Fig. 2. Effects of salinity on fecal coliforms in Bradley Creek.
p
Enterococcus
r2
F
df
p
0.01
0.006
>0.99
0.13
0.35
0.65
0.003
0.07
0.001
0.06
0.09
0.10
0.74
0.08
0.80
0.12
0.06
0.054
0.11
3.05
0.07
2.55
3.73
3.94
1,43
1,43
1,41
1,43
1,37
1,37
Fig. 3. Effects of temperature on fecal coliforms in Bradley Creek.
Multiple regression was used to evaluate the possibility that interactions among the
environmental parameters may have obscured relationships between concentrations of
fecal indicator bacteria and environmental parameters (using 72 hr rainfall instead of 48
hr rainfall). Results of this analysis are shown in Table 3, and demonstrate a significant
effect of 24 hr rainfall on fecal coliform bacteria concentrations in sediments. The
significant pair-wise relationships between fecal coliforms and temperature and salinity
are not significant in this analysis, suggesting that interactions among parameters mask
73
responses of fecal coliforms to individual parameters. Identification of a significant
rainfall effect agrees with observations from the July 1 sewage spill at Hewletts Creek
and subsequent spike in fecal coliform and enterococcus concentrations after a heavy
rain on July 14, 2005, discussed elsewhere in this report.
________________________________________________________________
Table 3. Results of multiple regression analysis of the effects of temperature, salinity,
carbohydrate, phosphorus, and 24 hr and 72 hr rainfall on fecal coliform concentrations
in sediments at Bradley Creek sites, Jan. 2003 – March, 2005. Significant effects in
bold.
2
Overall model r value was 0.16.
Source
df
SS
MS
F
Model
6
1
1
1
1
1
1
125
131
4022134
112
4021.5
458146
135988
2994796
143975
21404399
25426533
670356
112
4021.5
458146
135988
2994796
143975
171235
3.91
0.0007
0.0235
2.675
0.7941
17.49
0.84
Temperature
Salinity
Carbohydrate
Phosphorus
24 hr rainfall
72 hr rainfall
Error
Total
p
0.0013
0.9796
0.8784
0.1044
0.3746
<0.001
0.3609
Experimental manipulations of the availability of phosphorus and carbohydrate
evaluated the responses of fecal coliforms and enterococcus in sediment samples from
several locations with varying natural sediment P and carbohydrate levels. Results of
six experiments at five locations were analyzed by 2-way ANOVA and are shown in
Table 4. Added phosphorus supported significant growth of fecal enterococcus bacteria
when initial sediment P levels were relatively low, but fecal coliforms never responded
to added P. This latter response was consistent with the lack of any correlation between
sediment P and sediment fecal coliforms described earlier (Tables 2 and 3). However,
fecal coliform bacteria responded significantly to added dextrose, a form of bioavailable carbon, in three of six individual experiments and in the overall analysis. Fecal
enterococcus did not respond as frequently to added dextrose, but also showed a
significant response in the overall analysis, suggesting that both groups of fecal
indicator bacteria are more frequently limited by bio-available organic substrate than by
phosphorus.
Table 4. Effects of added phosphorus (P) and dextrose (C) and interactions of P and C (I)
on changes in fecal coliform (FC) and fecal enterococcus (FE) concentrations in sediment
samples from locations in New Hanover County. All treatment combinations run in
triplicate and bacteria concentrations log-transformed prior to analysis by 2-way ANOVA.
Significant effects in bold.
74
Site Date
Initial P
µg P/g sed.
Initial C
µg C/g sed.
Effect
FC
_____ FE
F
p
_____
F
p
E
8/19
19.6
420
C
P
I
29.9
0.65
0.89
0.001 11.9
0.44 7.00
0.37 0.01
0.009
0.029
0.92
E
7/22
31.2
628
C
P
I
0.02
3.53
57.6
0.89 2.38
0.09 5.71
0.001 0.00
0.16
0.04
1.00
BWP 8/29
47.0
290
C
P
I
1.71
1.05
0.39
0.23
0.34
0.55
4.5
0.50
0.50
0.07
0.49
0.49
210
74.4
290
C
P
I
2.60
3.36
8.04
0.15
0.10
0.02
0.08
0.50
0.50
0.78
0.49
0.49
REC 8/24
102
2990
C
P
I
7.71
0.22
0.47
0.02
0.65
0.51
4.91
0.48
0.78
0.06
0.51
0.40
CRT 9/6
176
3600
C
P
I
17.8
0.91
3.06
0.003 0.08
0.37 0.50
0.12 0.50
0.60
0.19
0.19
C
P
I
32.1
0.73
0.73
0.001 6.93
0.40 0.09
0.40 1.24
0.02
0.77
0.28
9/1
Combined Data
Analysis of storm water runoff in one event at a pond on the UNCW campus in the
Bradley Creek drainage revealed that soluble carbohydrates (a measure of bioavailable carbon) increased significantly, but temporarily, over background levels (Table
5). Thus, storm water runoff may provide fresh bio-available carbon in addition to its
role as a source mechanism for fecal bacteria that contaminate sediments.
Table 5. Response of soluble carbohydrates to rain events in a pond on the UNCW
campus.
Date
8/3/05
8/9/05
8/12/05
Condition
Dry
Rain
Dry
[Soluble Carbohydrates], µg C/L
525
1330
525
Std. Dev.
462
811
349
75
8/13/05
Dry
553
131
Discussion
Sediments in the Bradley Creek drainage frequently harbored significant populations of
fecal coliform 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.
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.
We must also consider the dangers posed by human sources of fecal contamination,
particularly spills from sewage systems, however, as dramatically demonstrated by the
spills in Hewletts Creek. Such large spills are fortunately rare, but analysis of the NC
Division of Water Quality violations data base revealed that sewage spills occurred at a
frequency of about once/week in New Hanover County during the period 1997-2004. At
such a high frequency, repeated contamination of sediments, where fecal indicator
bacteria are known to persist for weeks following initial recruitment, would drive
continuously elevated concentrations of these pollutants. Moreover, sewage itself is a
concentrated source of both phosphorus and bio-available organic carbon, so sewage
contamination provides both the microbes and their substrates, independent of any
storm water runoff effects. Obviously such spills must be reduced if New Hanover
County’s Tidal Creeks are to be kept safe for human uses.
Management of sediment contamination by fecal indicator bacteria and the pathogens
they represent could include efforts to limit inputs of the resources supporting their
survival and growth. Our results indicate that the macronutrient, phosphorus, does
appear to limit fecal enterococcus bacteria when present at very low concentrations.
However, in most aquatic sites we studied, sediment phosphorus concentrations were
76
higher than this threshold, indicating another limiting factor, which is likely to be bioavailable organic matter. Relatively little is known about sources and variability of bioavailable organic matter in this context, so it is premature to advocate management
approaches based on that criterion. The clear conclusion from our statistical analysis,
however, is that storm water runoff is the most significant factor driving sediment
contamination. Obviously, the challenge is to adopt and use effective storm water
management techniques if we intend to manage the threat posed by sediment bacteria
and pathogens successfully.
Acknowledgments: This research was supported by grants from the UNC Water
Resources Research Institute Project #2004NC36B and UNC Sea Grant R/MER-50 to
LBC and MAM.
Literature Cited
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American Public Health Association. Washington, D.C., A.E. Greenberg, ed.
Cahoon, L.B., B.R. Toothman, M.L. Ortwine, R.N. Harrington, R.S. Gerhart, S.L.
Alexander, and T.D. Blackburn. 2005. Fecal contamination of tidal creek sediments –
relationships to sediment phosphorus and among indicator bacteria, pp. 48-55, in
Environmental quality of Wilmington and New Hanover County watersheds 20032004, CMS Report 05-01, UNCW Center for Marine Science Research.
Dale, N.G. 1974. Bacteria in intertidal sediments: factors related to their distribution.
Limnol. Oceanogr. 19:509-518.
Doyle, J.D. 1985. Analyses of recreational water quality as related to sediment
resuspension. Dissertation Abstracts International. Part B. Science and Engineering.
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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.
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.
77
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.
rd
Sokal, R.R., and F.J. Rohlf. 1995. Biometry, 3
York, 887 pp.
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Struck, P.H. 1988. Relationship between sediment and fecal coliform levels in a Puget
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Tate, R.L., III. 1978. Cultural and environment factors affecting the longevity of
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Underwood, G.J.C., D.M. Paterson, and R.J. Parkes. 1995. The measurement of
microbial carbohydrate exopolymers from intertidal sediments. Limnol. Oceanogr.
40:1243-1254.
Valderrama, J.C. 1981. The simultaneous analysis of total nitrogen and phosphorus in
natural waters. Mar. Chem. 10:109-122.
14.0 Evaluation of Oyster Characteristics in
Pages, Howe, and Hewletts Creeks
Martin Posey and Troy Alphin
Center for Marine Science
University of North Carolina Wilmington
Introduction
The ecological health of the tidal creeks in New Hanover County has been a topic of
concern for the last decade. With increased development within the watershed and
associated increased inputs from upland areas, storm water runoff, and unexpected
78
inputs from failing sewer lines, the public scrutiny of these issues and the question of
the human health and safety associated with the tidal creeks also has become a central
issue over the last two years. Some of the long-time residents within the tidal creek
watersheds have expressed concern over what they see as a decline in the fishery
resource within the creeks and changes in the physical characteristics of the tidal
creeks based on anecdotal accounts of channel depth. Likewise, concerns have been
expressed by the local oystermen and commercial fishermen who relay accounts of
dwindling shellfish beds and increased fishing pressure on the remaining open,
managed bottom areas. Similar concerns have been expressed by conservation
groups. The Southeastern Regional Oyster Steering Committee gathered comments
from a number of groups and individuals including residents, fishermen, and grassroots
community environmentalists during 2004 and 2005. Although a variety of opinions
were expressed, there was agreement on a number of issues: 1) Oyster stocks within
the southern regions (especially New Hanover and Onslow Counties) seem to be
declining, 2) This decline is directly related to the closure of shellfish grounds due to
failure of these areas to meet shellfish sanitation standards, 3) The reduction in overall
acreage available to shellfish harvest has increased the fishing pressure on the
remaining shellfish bottom, in some instances leading to “apparent” overharvest, and 4)
Closure of public bottom to shellfish harvest seems to closely track upland development
within the watershed. Several recommendations were taken to MFC’s Shellfish
Advisory Committee from this group, including a request for more managed bottom
areas within the southern region and a request for greater restrictions on harvest limits.
Currently DMF has reviewed these requests and in most instances the director has
proclamation authority, meaning he can establish additional managed areas and revise
catch limits as needed. However these proposed changes do not address the under
lying issues of impaired estuarine ecosystem function and potential impacts to
ecosystem health.
Rationale
The UNCW Benthic Ecology Laboratory has conducted work in the tidal creek systems
of New Hanover County since 1990 on projects ranging from general bivalve surveys to
evaluations of eutrophication, and most recently evaluation of ecosystem health
through indicator species such as the oyster Crassostrea virginica. Oysters represent
both an important commercial target species with a dockside value in NC of over $10
million. During the 2005 sampling year we concentrated our effort on three target
creeks; Pages Creek, Howe Creek, and Hewletts Creek. In general, Pages Creek has
been considered the least impacted of the three systems, supporting shellfish and a
PNA (primary nursery area), indicating that this area is critical to supporting local
populations of commercially and recreationally important finfish and crustaceans.
Howe Creek has experienced problems in previous years with increased sediment
loads and nutrients from surrounding developments. Hewletts Creek is considered one
79
of the most impacted of the tidal creeks in New Hanover County due to increased
sedimentation, nutrient runoff and shellfish closures throughout most of the creek. Our
study focused on evaluating the actual condition of the oyster stocks in each of these
creek systems. Oyster density, size, and condition were evaluated for three
independent reefs in each creek.
Methods
In summer 2005, the Benthic Ecology Laboratory sampled oyster populations in
Hewletts Creek, Howe Creek, and Pages Creek. Live oyster density, percent shell
cover, size demography, condition, shell height, and rugosity (vertical complexity) were
measured on three randomly selected oyster reefs in the lower portion of each creek.
Previous work and aerial photography indicated that oyster coverage within the three
creeks was greatest in the lower kilometer of each, although the extent of coverage
varied among creeks.
Quadrate sampling: Each reef was sampled by random placement of ten 50cm x 50cm
square quadrates. Percent shell cover was estimated visually by observing the percent
of the area within a quadrate covered by oyster shell (both shell hash and live oysters). In
order to determine oyster density, the number of live oysters within a quadrate was
counted. The size demography of the oysters on each reef was calculated by measuring
a random selection of twenty live oysters per quadrate. For the purposes of this study,
size was represented as shell height (long axis of the oyster from umbo to outer edge
expressed in mm).
Reef characteristic: The average height of the shell matrix on a reef was determined by
measuring the highest point in each quadrate, from the sediment to the tip of the tallest
shell. Rugosity was randomly sampled at five points per reef. A 100cm chain was
draped across the reef in a straight line. The straight distance of the conformed chain
was then measured from end to end and its length recorded. The shorter the length the
more rugose or “jagged” (vertically complex) the topography of the reef.
Oyster characteristics: Oyster condition was assessed visually using 15 oysters from
each of 2 size classes (i.e. small- 40-50mm, large- +75mm). Each oyster was given a
numerical condition code depending on the appearance of their tissues (Quick and
Mackin 1971). Condition index, a ratio of soft tissue dry weight to internal shell volume,
will also be calculated for those oysters and information made available in future reports.
This is a measure of soft tissue growth and is considered to be an indicator of oyster
health. In order to determine the internal shell volume, a water displacement method will
be used. The volume of water displaced when the whole oyster and when the shucked
oyster (i.e. empty shell) is placed in a graduated cylinder will be recorded. Dry tissue
weight will be obtained once the oyster tissues have been dried for 24 hours at 70°C.
Results and Discussion
Oyster Characteristics: Overall oyster populations in the three creek systems seem
very similar with only modest differences in most parameters. Percent shell cover was
greatest in Pages Creek, on average ~10% greater coverage that oyster reefs in Hewletts
80
Creek and ~28% greater coverage than oyster reefs in Howe Creek (Figure 1). It seems
likely that that lower cover of exposed shell in Howe and Hewletts Creeks may be a
function of increased suspended solids and subsequent sedimentation compared to
Pages Creek, rather than increased oyster production in Pages creek. Oyster size,
indicated here as shell height (long axis of the oyster from umbo to outer edge), showed
no difference among creeks (Figure 2). Mean size was ~54mm in Hewletts and Howe
Creeks and ~58mm in Pages creek. Legal harvest size of oysters is three inches
(~77mm). Average density of oysters did vary among creeks, with greater densities in
2
2
Howe Creek (68 oyster m ) and lowest in Pages (42 oyster m ) while densities in Hewletts
Creek fell in the middle of this range (Figure 3). While these mean densities are not
surprising, peak densities have previously been recorded that exceed 125 live oysters per
0.25 m2 (Alphin and Posey unpublished data).
Reef Characteristics: Vertical complexity is a good indicator of reef function as habitat
and suitability for spat settlement. Here we use rugosity as a proxy for vertical complexity,
where a lower number indicates more vertical relief of a reef, with numerous upright
oyster clumps, and a higher number (approaching 1) would indicate a reef that may be in
decline or suffering from high sedimentation. A priori we expected reefs in Pages Creek to
exhibit a greater degree of vertical complexity. This was not the case since all three
creeks showed similar measures of complexity, with Hewletts Creek showing slightly
higher rugosity and Howe Creek slightly lower than Pages Creek (Figure 4). The other
reef characteristic that we measured was shell height (distance from substrate surface to
the top of the reef). This provides a measure of reef development and mounding of the
oyster reefs. Reef height has also been suggested as a potential response variable to
sedimentation, since oysters settling in areas experiencing heavy sedimentation would
have a greater chance of survival by setting on the upper edge of the reef. It follows that
in areas with heavy sedimentation that the upper edges of the reef are also the areas
most likely to provide clean settlement substrates, since shells within the reef are more
likely to be cover with sediment. Results of the current study show a trend towards
greater reef height in Hewletts Creek (Figure 5).
Conclusions
For both oyster characteristics and reef characteristics there were few clear patterns
indicating a difference in oyster health among the creeks. A priori we had expected
Pages Creek to show characteristics of healthier oysters or better-developed reefs
compared to either Hewletts or Howe Creeks. Percent shell cover was greatest in
Pages Creek, on average ~10% greater coverage that oyster reefs in Hewletts Creek
and ~28% greater coverage than oyster reefs in Howe Creek. It seems likely that that
lower cover of exposed shell in Howe and Hewletts Creeks may be a function of
increased suspended solids and subsequent sedimentation compared to Pages Creek,
rather than increased oyster production in Pages creek. Howe Creek showed the
greatest oyster density and no apparent difference in oyster size was seen among the
creeks. Where we did detect differences (reef height and shell cover) these supported
the idea of increased sedimentation in Hewletts and Howe Creeks compared to Pages
Creek. While we know that water quality in Hewletts Creek has suffered for some time,
the current data does not provide evidence for population differences among the
81
creeks. However, population measures may reflect regional conditions more than local
creek conditions because of interchange among the creek systems through the
IntraCoastal Waterway. Even with similar densities and reef form, differences may be
apparent with physiological or condition measures such as tissue weight and disease
incidence. Ongoing work is examining both condition index and disease. Currently we
are using the traditional thyoglycate method for evaluate the disease intensity for
oysters in these three target creeks and will compare disease intensity and condition of
these oyster populations.
Percent Shell Cover
100
91.83
90
82.77
80
Shell Cover (%)
70
64.9
60
Hewletts
Howe
Pages
50
40
30
20
10
0
Figure 1. Mean percent shell cover, including live oysters and dead
shell.
82
Oyster Size
100
90
80
Size (mm)
70
60
58.52
54.57
54.82
Hewletts
Howe
Pages
50
40
30
20
10
0
Figure 2. Mean size (shell height) of oyster per creek.
Oyster Density
100
90
Density (per .25 m sq)
80
68.07
70
60
51.13
50
42.23
40
30
20
10
0
Figure 3. Mean live oyster density per creek.
Hewletts
Howe
Pages
83
Reef Rugosity
100
90
80
Rugosity (cm)
70
68.95
66.2
61.17
60
Hewletts
Howe
Pages
50
40
30
20
10
0
Figure 4. Mean vertical complexity
Reef Height
20
18
16
14
15.37
13.48
Height (mm)
12.53
12
Hewletts
Howe
Pages
10
8
6
4
2
0
Figure 5. Mean reef height from substrate surface to top of reef.
84
15.0 Report References Cited
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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
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86
16.0 Acknowledgments
Funding for this research was provided by New Hanover County, the City of
Wilmington, the North Carolina Clean Water Management Trust Fund, the US EPA 319
Program through North Carolina State University, 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, Ed Beck and Dave Weaver. For field and
laboratory assistance we thank Matt McIver, Brad Rosov, Rena Spivey, Kimberly
Duernberger and Cinnamon Williams
87
17.0 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
88
18.0 Appendix B. UNCW ratings of sampling stations in Wilmington and New Hanover
County tidal creek watersheds based on August 2004 – July 2005 data for tidal creeks
and January -September 2005 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
G
P
Bradley Creek
BC-CA
BC-CR
BC-SB
BC-SBU
BC-NB
BC-NBU
BC-76
G
G
G
G
G
G
G
P
G
G
G
F
G
G
G
G
G
G
G
G
G
P
-
Burnt Mill Creek
BMC-KA1
BMC-KA3
BMC-AP1
BMC-AP3
BMC-WP
BMC-PP
G
G
G
P
G
F
P
P
G
G
P
P
G
G
F
G
G
G
P
P
P
F
P
P
Futch Creek
FC-4
FC-6
FC-8
FC-13
FC-17
FOY
G
G
G
G
G
G
G
G
G
G
G
G
G
G
G
G
G
G
G
G
G
G
G
G
Greenfield Lake
GL-LC
GL-JRB
GL-LB
GL-2340
GL-YD
GL-P
G
F
G
P
P
P
P
P
P
P
F
G
G
G
G
G
G
G
P
P
P
F
F
P
89
Watershed
Station
Chlor a
DO
Hewletts Creek**
HC-M
HC-2
HC-3
HC-NWB
NB-GLR
MB-PGR
SB-PGR
PVGC-9
DB-1
DB-2
DB-3
DB-4
G
G
G
G
G
G
G
G
G
G
G
G
G
G
G
P
F
G
P
G
P
P
G
G
G
G
G
G
G
G
G
G
G
G
G
G
F
G
G
F
P
P
F
P
P
P
P
P
Howe Creek
HW-M
HW-FP
HW-GC
HW-GP
HW-DT
G
G
G
G
G
G
G
G
F
G
G
G
G
G
G
G
G
G
F
P
Motts Creek
MOT-RR
G
P
G
P
Pages Creek
PC-M
PC-BDDS
PC-BDUS
G
G
G
G
G
F
G
G
G
-
Smith Creek
SC-23
SC-CH
G
G
P
P
G
G
F
G
Whiskey Creek
Turbidity
Fecal coliforms*
WC-NB
G
G
G
WC-SB
G
G
G
WC-MLR
G
G
G
WC-AB
G
G
G
WC-MB
G
G
G
_____________________________________________________________________
*fecal coliform category used here is based on the human contact standard of 200
CFU/100 mL, not the shellfishing standard of 14 CFU/100 mL.
**These ratings are based only on the results of the regular monthly sampling program.
The July sewage spill temporarily led to excessive July fecal coliform counts and algal
blooms, and low dissolved oxygen.
90
19.0 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
BNC-CB
BNC-EF
BNC-AW
BNC-RR
N 34.16823
N 34.15867
N 34.16937
N 34.16483
N 34.15873
W
W
W
W
W
77.93218
77.91190
77.92485
77.92577
77.93795
Bradley Creek
BC-CA
BC-CR
BC-SB
BC-SBU
BC-NB
BC-NBU
BC-76
N 34.23257
N 34.23077
N 34.21977
N 34.21725
N 34.22150
N 34.23265
N 34.21473
W
W
W
W
W
W
W
77.86658
77.85235
77.84578
77.85410
77.84405
77.92362
77.83357
Burnt Mill Creek
BMC-KA1
BMC-KA3
BMC-AP1
BMC-AP2
BMC-AP3
BMC-WP
BMC-PP
N 34.22207
N 34.22280
N 34.22927
N 34.22927
N 34.22927
N 34.24083
N 34.24252
W
W
W
W
W
W
W
77.88506
77.88601
77.86658
77.89792
77.90143
77.92419
77.92510
Futch Creek
FC-4
FC-6
FC-8
FC-13
FC-17
FOY
N 34.30127
N 34.30298
N 34.30423
N 34.30352
N 34.30378
N 34.30705
W
W
W
W
W
W
77.74635
77.75070
77.75415
77.75790
77.76422
77.75707
Greenfield Lake
GL-SS1
GL-SS2
GL-LC
GL-JRB
GL-LB
GL-2340
GL-YD
GL-P
N 34.19963
N 34.20038
N 34.20752
N 34.21260
N 34.21445
N 34.19857
N 34.20702
N 34.21370
W
W
W
W
W
W
W
W
77.92447
77.92952
77.92980
77.93140
77.93553
77.93560
77.93120
77.94362
91
Hewletts Creek
HC-M
HC-2
HC-3
HC-NWB
NB-GLR
MB-PGR
SB-PGR
PVGC-9
DB-1
DB-2
DB-3
DB-4
N 34.18230
N 34.18723
N 34.19023
N 34.19512
N 34.19783
N 34.19807
N 34.19025
N 34.19165
N 34.1764
N 34.1781
N 34.1799
N 34.1789
W
W
W
W
W
W
W
W
W
W
W
W
77.83888
77.84307
77.85083
77.86155
77.86317
77.87088
77.86472
77.89175
77.8775
77.8805
77.8798
77.8752
Howe Creek
HW-M
HW-FP
HW-GC
HW-GP
HW-DT
N 34.24765
N 34.25443
N 34.25448
N 34.25545
N 34.25562
W
W
W
W
W
77.78718
77.79488
77.80512
77.81530
77.81952
Motts Creek
MOT-RR
N 34.15867
W 77.91605
Pages Creek
PC-M
PC-OL
PC-CON
PC-OP
PC-LD
PC-BDDS
PC-WB
PC-BDUS
PC-H
N 34.27008
N 34.27450
N 34.27743
N 34.28292
N 34.28067
N 34.28143
N 34.27635
N 34.27732
N 34.27508
W
W
W
W
W
W
W
W
W
Smith Creek
SC-23
SC-CH
N 34.25795
N 34.25897
W 77.91967
W 77.93872
Upper and Lower
Cape Fear
UCF-PS
LCF-GO
N 34.24205
N 34.21230
W 77.94838
W 77.98603
Whiskey Creek
77.77133
77.77567
77.77763
77.78032
77.78495
77.79417
77.79582
77.80153
77.79813
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
_____________________________________________________________________
92
20.0 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,
93
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.
Mallin, M.A., L.B. Cahoon, M.H. Posey, V.L. Johnson, D.C. Parsons, T.D. Alphin, B.R.
Toothman and J.F. Merritt. 2005. Environmental Quality of Wilmington and New
Hanover County Watersheds, 2003-2004. CMS Report 05-01, 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.
94
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.
Mallin, M.A., S.H. Ensign, D.C. Parsons, V.L. Johnson, J.M. Burkholder and P.A.
Rublee. 2005. Relationship of Pfiesteria spp. and Pfiesteria-like organisms to
environmental factors in tidal creeks draining urban watersheds. pp 68-70 in
Steidinger, K.A., J.H. Landsberg, C.R. Tomas and G.A. Vargo, (Eds.) XHAB,
Proceedings of the Tenth Conference on Harmful Algal Blooms, 2002, Florida Fish
and Wildlife Conservation Commission, Florida Institute of Oceanography, and
Intergovernmental Commission of UNESCO.