ENVIRONMENTAL QUALITY OF WILMINGTON AND
NEW HANOVER COUNTY WATERSHEDS
2005-2006
by
Michael A. Mallin, Lawrence B. Cahoon, Troy D. Alphin, Martin H. Posey,
Brad A. Rosov, Douglas C. Parsons, Renee N. Harrington
and James F. Merritt
CMS Report 07-01
Center for Marine Science
University of North Carolina Wilmington
Wilmington, N.C. 28409
www.uncw.edu/cmsr/aquaticecology/tidalcreeks
February 2007
Funded by:
The City of Wilmington, New Hanover County and the US EPA 319 Program (through
NC Division of Water quality and North Carolina State University)
2
Executive Summary
This report represents combined results of Year 12 of the New Hanover County Tidal
Creeks Project and Year 8 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 52 sampling stations. In this summary
we first present brief water quality overviews for each watershed from data collected
between August 2005 – September 2006, 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 low dissolved oxygen and fair water quality in terms of fecal coliform
counts. It also had among the highest suspended solids, ammonium, total nitrogen and
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 were sampled, all from shore. Turbidity was not problematic during 20052006. Dissolved oxygen was good to fair at all sites except the branch at College Acres
(BC-CA) and the north branch (BC-NB) at Wrightsville Avenue where there was
ongoing bridge construction. Elevated nitrogen and phosphorus levels enter the creek
in both the north and south branches, and two major algal blooms occurred in the creek
in the south branch (BC-SB) at Wrightsville Avenue. Fecal coliform bacteria samples
were collected at all stations, with poor microbiological water quality at four of the six
sites (BC-CA, BC-CR (at College Acres), BC-SB and BC-SBU (upper south branch).
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 2006, but the
creek showed poor water quality in terms of substandard dissolved oxygen, with four
out of six stations having dissolved oxygen concentrations below the State standard >
25% of the times sampled. High fecal coliform counts were another major problem,
with all six sites exceeding the human contact standard > 25% of occasions sampled.
There were also algal bloom problems at the Wallace Park and Princess Place stations.
The effectiveness of Ann McCrary wet detention pond as a pollution control device was
poor during 2006. While the pond led to a significant reduction in nitrate and turbidity
and an increase in dissolved oxygen, it failed to reduce other nutrient concentrations
including ammonium and total nitrogen, and actually led to a significant increase in 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.
3
The constructed wetland on Kerr Avenue led to a statistically significant decrease in
nitrate, but none of the other nutrient species (although decreases in ammonium and
fecal coliform bacteria counts were nearly significant).
Sediments were sampled for metals and polycyclic aromatic hydrocarbons (PAHs urban-derived toxic compounds). Most of the stations had sediment metals
concentrations that were well below levels considered potentially toxic to benthic
organisms. One exception was lead, which exceeded known potentially toxic levels at
the Wallace Park station BMC-WP and the Princess Place station (BMC-PP). Lead
concentrations at BMC-KA1 approached harmful concentrations but did not exceed
them. Copper exceeded potentially toxic levels at KA-1 but was much reduced at the
output station KA-3; copper concentrations were close to the ERL (low toxic range) at
BMC-WP and AP-3. Additionally, while not exceeding toxic levels both cadmium and
zinc approached them at BMC-WP. All of the PAH sediment samples exceeded known
toxic concentrations except for Station AP3, below Ann McCrary Pond, where PAHs
were below the detection limit. Sediment metals and PAH concentrations in general
were similar to those of 2005 except for the increased copper at KA1 and lead at BMCWP and BMC-PP. Compared with sediment samples taken in 1999 at BC-PP, there
was a decrease in copper, chromium, lead, and zinc in 2006. This may have been a
result of burial of contaminated sediments by further sedimentation, or flushing from
storm-induced flooding.
Futch Creek – Futch Creek is situated on the New Hanover-Pender County line and
drains into the ICW. Six locations were sampled by boat. Futch Creek maintained
good microbiological water quality in the lower stations and Foy Creek, as it has since
channel dredging at the mouth occurred in 1995 and 1996. However, the State fecal
coliform bacteria water contact standard of 200 CFU/100 mL of water was exceeded on
two occasions at FC-13 and on five of 12 occasions at FC-17, both stations in the upper
south branch. Algal blooms, turbidity, and low dissolved oxygen were not problems in
2005-2006. This creek continues to display good water quality relative to other creeks
in the New Hanover County tidal creek system, due to generally low development and
impervious surface coverage in its watershed; however, fecal coliform counts have
indicated deteriorating water quality in two of the past three years sampled.
Greenfield Lake – This urban lake was sampled at three tributary sites and three in-lake
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 well in excess of the state standard for
human contact waters.
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. Eight
algal blooms exceeding the state standard of 40 µg/L were recorded in our sampling
during 2006 (a slight 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).
Low dissolved oxygen and high fecal coliform counts were found only at the uppermost
4
lake station GL-2340. However, high biochemical oxygen demand (BOD5 > 3.0 mg/l)
occurred frequently at the in-lake stations. Thus, during 2006 Greenfield Lake was
impaired by algal blooms, high fecal coliform counts, high BOD and low dissolved
oxygen concentrations, although the latter parameter continues to be better than the
2003-2004 period. One fish kill of < 100 fish occurred in February 2006 from unknown
causes.
In spring of 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. Some macrophyte growth appeared in spring 2006 so
herbicide was applied in March and April and 500 more grass carp were added to the
lake. As mentioned, eight algal blooms exceeding the state standard of 40 µg/L were
recorded among the three in-lake sampling stations during 2006 (an increase over the
previous year). Despite the blooms, there was good dissolved oxygen at two of the
stations in 2006 (especially nearest the SolarBees), but low dissolved oxygen
concentrations were measured at GL-2340, near the upper lake. In 2006 there was a
highly statistically significant relationship within the lake between chlorophyll a and
BOD5, meaning that the algal blooms are an important cause of low dissolved oxygen
in this lake. Thus, a challenge for Greenfield Lake is to reduce the frequency and
magnitude of the algal blooms, which will lead to continuing dissolved oxygen
improvements.
Hewletts Creek – Hewletts Creek drains a large watershed into the Intracoastal
Waterway. In 2006 the creek was sampled at eight tidal sites and five non-tidal
freshwater sites. There were several incidents of hypoxia seen in our regular monthly
2005-2006 sampling; three at NB-GLR (the north branch at Greenville Loop Rd.) and
five at SB-PGR (the south branch at Pine Grove Rd.), although none were severe
(below 3.0 mg/L). Fecal coliform bacteria were not sampled at the tidal stations in
2006. Three minor algal blooms (chlorophyll a of 18-31 µg/L) occurred at NB-GLR and
one at SB-PGR. A sewage leak occurred in late February in the watershed of the
middle branch which led to high (2,000-20,000 CFU/100 mL) fecal coliform counts in
the upper stations until early March.
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 71% of the time in
2006 at PVGC-9, and the counts had a geometric mean of 530 CFU/100 mL. The
other sites are being sampled to gain pre and post construction information on the
water quality of streams entering (DB-1, DB-2, DB-3) and exiting (DB-4) a constructed
wetland/future park area known as the Dobo site, draining into the headwaters of
Hewletts Creek. In 2006 all nutrient species except nitrate had the highest
concentrations at DB-1 and lowest at DB-2. There was some reduction of nutrients at
5
DB-4 compared with DB-1 (particularly ammonium), showing that the property already
has some function in water quality improvement. The exception was nitrate, which
showed an increase at DB-4 compared with DB-1. Dissolved oxygen was particularly
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 high at all sites, particularly DB-1 and DB-4 (these
sites are essentially drainage ditches). 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 2005-2006. Turbidity did not exceed North Carolina water quality standards at
any of the stations. Dissolved oxygen concentrations were generally good in lower
Howe Creek and fair in upper Howe Creek. Nutrient levels were generally low except
for nitrate at HW-DT, the uppermost creek station. Nitrate levels showed an increase
over levels in 2004-2005. There was one minor algal bloom of 61 µg/L as chlorophyll a
at HW-DT. Since wetland enhancement was performed in 1998 above Graham Pond
the creek below the pond at Station 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 stations.
HW-GP exceeded the North Carolina human contact standard on six of 12 occasions,
and HW-DT also exceeded the standard on six of 12 occasions. The 2005-2006 data
show a worsening in fecal coliform counts after somewhat better bacterial water quality
that were seen in Howe Creek in 2004-2005.
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 5.0 mg/L on six of seven occasions in 2006 (minimum 3.7 mg/L) similar to
previous years. Like the previous year, neither turbidity nor suspended solids were
problematic in 2006. Fecal coliform contamination was a severe problem in Motts
Creek, with the geometric mean of 657 CFU/100 mL well exceeding the State standard
of 200 CFU/100 mL, and samples exceeding this standard on all seven 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
concentrations were low to moderate, with no algal blooms detected in 2006. BOD5
samples yielded a mean value of 1.4 mg/L and a median value of 1.4 mg/L, generally
higher than the previous year. Thus, this creek showed mixed water quality, with no
algal bloom or turbidity problems, but poor dissolved oxygen and fecal coliform
conditions.
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 low dissolved oxygen during summers of 2005 and 2006, 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 except for two algal
blooms of 18 and 32 µg/L noted at PC-BDDS and PC-BDUS, respectively. Because of
6
the relatively low watershed development and low amount of impervious surface
coverage in the watershed, this is one of the least-polluted 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 2006. Dissolved oxygen
concentrations were below 5.0 mg/L on three of seven occasions at both SC-23 and
SC-CH, between April and September 2006; however, these readings were not
severely hypoxic. Thus, low dissolved oxygen was a minor water quality problem in
Smith Creek. The North Carolina turbidity standard for estuarine waters (25 NTU) was
not exceeded during 2006. Nutrient concentrations remained similar to previous years,
and one major algal bloom occurred at SC-23 in August 2006 (48 µg/L). Fecal coliform
bacteria concentrations were above 200 CFU/100 mL on two occasions at each station,
somewhat poorer than the previous year. BOD5 was sampled at SC-CH, with a mean
value of 1.1 mg/L and a median value of 1.2 mg/L, an improvement over the previous
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 2005-2006, with no algal blooms. Dissolved oxygen concentrations
were below the State standard on three of 12 occasions at both WC-MLR and WC-AB
in 2005-2006, but high turbidity was not a problem. Fecal coliform bacteria were not
sampled in 2005-2006 in Whiskey Creek.
Water Quality Station Ratings – The UNC Wilmington Aquatic Ecology Laboratory
utilizes a quantitative system with four parameters (dissolved oxygen, chlorophyll a,
turbidity, and fecal coliform bacteria) to rate water quality at our sampling sites. If a site
exceeds the North Carolina water quality standard for a parameter less that 10% of the
time sampled, it is rated Good; if it exceeds the standard 10-25% of the time it is rated
Fair, and if it exceeds the standard > 25% of the time it is rated Poor for that parameter.
We applied these numerical standards to the water bodies described in this report,
based on 2005-2006 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 fair water quality.
Five of the seven stations in Bradley Creek were rated as poor in 2006, and the other
was rated fair. All six stations in Burnt Mill Creek were rated as poor in terms of fecal
coliform bacteria. Futch Creek was rated as good for fecal coliform bacteria in the
lower creek, including for shellfishing; however, one of the upper stations fell to a poor
rating and one to a fair rating. The Greenfield Lake tributaries were rated as poor
microbiological water quality and the three in-lake stations as good, fair and poor,
respectively. The non-tidal freshwater stations in the Hewletts Creek watershed are
essentially drainage ditches, and were poor throughout. The uppermost two stations in
Howe Creek were rated poor and the lower three were rated good. Lower Motts Creek
was rated poor, and the two stations in Smith Creek were both rated poor. We also list
our ratings for chlorophyll a, dissolved oxygen and turbidity in Appendix B.
7
Fecal coliform bacterial conditions for the entire Wilmington City and New Hanover
County Watersheds system (39 sites sampled for fecal coliforms) showed 23% to be in
good condition, 10% in fair condition, and 67% in poor condition. Dissolved oxygen
conditions system-wide (52 sites) showed 30% of the sites were in good condition, 35%
were in fair condition, and 35% were in poor condition. For chlorophyll a, 88% of the
stations were rated as good, 4% as fair and 8% as poor.
8
Table of Contents
1.0
1.1
2.0
3.0
4.0
5.0
6.0
6.1
7.0
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
21.0
Introduction
9
Methods
9
Barnards Creek
12
Bradley Creek
15
Burnt Mill Creek
18
Futch Creek
25
Greenfield Lake
29
Continuing Assessment of Greenfield Lake Restoration Measures
33
Hewletts Creek
41
Howe Creek
48
Motts Creek
53
Pages Creek
56
Smith Creek
59
Whiskey Creek
62
Results of the Aerial Infrared Survey of City Watersheds
65
Boat Ramp Fecal Bacteria Study
69
Evaluation of Oyster Characteristics
82
References Cited
93
Acknowledgments
95
Appendix A: Selected N.C. water quality standards
96
Appendix B: UNCW Watershed Station Water Quality Ratings
97
Appendix C: GPS coordinates for the New Hanover County Tidal Creek
and Wilmington Watersheds Program sampling stations
99
Appendix D: UNCW reports and papers related to tidal creeks
101
9
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). Data from that report were later published in the peer-reviewed literature
(Mallin et al. 2000; Mallin et al. 2001) and were used in 2006 by the N.C. General
Assembly (Senate Bill 1566) as the scientific basis to redefine low density coastal areas
as 12% impervious surface coverage instead of the previously used 25% impervious
cover. 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; 2006). In the present
report we present results of continuing studies from August 2005 - July 2006 in the tidal
creek complex and January - September 2006 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 Water Quality 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
10
vertical profiles obtained by a Li-Cor LI-1000 integrator interfaced with a Li-Cor LI-193S
spherical quantum sensor.
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 six occasions within the Wilmington City watersheds from
January through September 2006. 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).
11
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 2006 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 6.5 ppt with a range of 0.4-14.5 ppt. This station
had dissolved oxygen levels ranging from 2.0-5.0 from June through September, with
three of those months having DO less than 3.8 mg/L. 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 (14
NTU), and did not exceed the state standard for estuarine waters of 25 NTU. Average
total suspended solids concentrations were the highest among area creeks, but there
were no algal bloom problems (Table 2.1). BOD5 was sampled seven times at BNCRR last year, yielding a median of 1.4 mg/L and a mean of 1.4 mg/L, which was similar
to the BOD5 concentrations found last year (Mallin et al. 2006). Fecal coliform counts
exceeded the state standard on only one of seven occasions, slightly better than the
previous year. Thus, in 2006 this station was impaired by low dissolved oxygen, with
comparatively high nutrient concentrations as well.
12
Table 2.1. Mean and standard deviation of water quality parameters in Barnards Creek
watershed, January - September 2006. Fecal coliforms as geometric mean; N/P ratio as
median (n = 7 for all parameters).
_____________________________________________________________________
Parameter
BNC-RR
mean (st. deviation)
range
_____________________________________________________________________
DO (mg/L)
5.4 (3.2)
2.0-11.7
Turbidity (NTU)
14 (4)
9-22
TSS (mg/L)
21.4 (7.6)
12.0-32.0
Nitrate (mg/L)
0.160 (0.153)
0.013-0.470
Ammonium (mg/L)
0.243 (0.177)
0.050-0.500
TN (mg/L)
1.350 (0.342)
0.910-1.960
Phosphate (mg/L)
0.077 (0.050)
0.010-0.171
TP (mg/L)
0.130 (0.070)
0.060-0.270
N/P molar ratio
7.8
Chlorophyll a (µg/L)
5.5 (5.5)
1.3-17.3
BOD5
1.4 (0.4)
0.7-2.0
Fecal coliform bacteria (/100 mL)
55
3-760
_____________________________________________________________________
13
14
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 2005-2006 (Table 3.1). The
standard of 25 NTU was not exceeded during our sampling. There were some
problems with low dissolved oxygen (hypoxia), with BC-NB having DO < 5.0 mg/L on
three occasions and BC-CA having substandard dissolved oxygen conditions on six of
seven sampling occasions (Appendix B).
Table 3.1 Water quality parameter concentrations at Bradley Creek sampling stations,
August 2005-July 2006. 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
31.4 (1.8)
28.3-34.3
4 (2)
1-6
6.7 (1.8)
4.3-10.2
10
2-95
BC-SB
11.8 (9.4)
0.6-26.7
8 (8)
2-31
7.4 (2.3)
4.7-10.9
215
56-2000
BC-SBU
0.1 (0.0)
0.0-0.1
2 (2)
0-6
7.3 (1.7)
5.0-11.4
209
110-1885
BC-NB
21.3 (7.6)
11.3-30.7
5 (2)
3-8
5.6 (2.2)
3.5-10.4
61
12-343
BC-NBU
0.1 (0.0)
0.1-0.1
6 (3)
2-13
7.4 (1.3)
5.6-10.4
164
48-2000
BC-CR
0.1 (0.0)
0.1-0.1
2 (3)
0-10
7.7 (1.0)
6.0-9.4
192
42-2000
BC-CA
0.1 (0.0)
9 (13)
5.0 (2.4)
294
0.0-0.1
0-37
3.4-10.5
48-8000
_____________________________________________________________________
Bradley creek showed severe fecal coliform bacteria pollution in 2005-2006, with
elevated counts exceeding the State standard of 200 CFU/100 mL occurring on 33% of
15
the occasions sampled at Stations BC-SB, BC-SBU, BC-NBU and BC-CR, with BC-CA
exceeding the standard on six of seven collections for an 86% exceedence rate (Table
3.1). Thus, five of the seven stations were rated as poor in terms of fecal coliform
bacteria counts (Appendix B).
Nitrate concentrations were highest at stations BC-CR, BC-CA, BC-SBU and BC-NBU.
Nitrate was generally similar to the previous year (Mallin et al. 2006). 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 2005-2006 except at
BC-SB, which had blooms of 47 and 40 µg/L in April and July, respectively (Table 3.2).
Table 3.2. Nutrient and chlorophyll a data at Bradley Creek sampling stations, August
2005-July 2006. 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
0.025 (0.042)0.016 (0.016)0.011 (0.007)2.6 (2.6)
0.003-0.145
0.001-0.054
0.005-0.028
0.3-10.1
0.034 (0.034)0.031 (0.033)0.014 (0.010)12.6 (15.5)
0.005-0.101
0.001-0.102
0.004-0.040
0.3-47.0
0.068 (0.046)
0.025-0.162
0.2-13.5
NA
0.010 (0.006)2.4 (3.8)
0.001-0.025
0.030 (0.040)0.036 (0.040)0.009 (0.006)4.4 (4.0)
0.002-0.108
0.001-0.123
0.003-0.019
0.3-13.4
0.068 (0.036)
0.024-0.142
NA
0.009 (0.014)1.2 (1.9)
0.001-0.049
0.1-6.9
0.277 (0.118)
0.094-0.602
NA
0.005 (0.005)1.8 (2.7)
0.001-0.016
0.1-10.0
0.078 (0.041)0.129 (0.030)0.027 (0.014)5.1 (4.3)
0.013-0.130
0.080-0.170
0.010-0.040
1.4-12.8
_____________________________________________________________________
NA = not analyzed
16
Figure 3.1. Bradley Creek watershed and sampling sites.
17
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), and 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 periodically hosts a thick growth of submersed aquatic
vegetation, with Hydrilla verticillata, Egeria densa, Alternanthera philoxeroides,
Ceratophyllum demersum and Valliseneria americana having been common at times.
There have been efforts to control this growth, including addition of triploid grass carp
as grazers. A 1998 survey also found that this pond was 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). Numerous waterfowl utilize this pond as well.
In 2005 sampling began on the inflow (BMC-KA1) and outflow (BMC-KA3) channels of
the Kerr Avenue constructed wetland (Fig. 4.1). This 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 second year of 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, nitrate, was significantly lowered by the pond, and ammonium
concentrations showed a nearly significant decrease (p = 0.074). There were no
differences in the other nutrient species. BOD5 concentrations were highly variable
entering the pond and much less variable leaving the pond, but overall there was no
significant difference in concentrations leaving the pond. However, on two occasions
when BOD5 was unusually high entering the pond (> 6.0 mg/L) reductions of over 70%
were realized. Fecal coliform bacteria were high entering the pond (geometric mean of
1382 CFU/100 mL), and reduced to a geometric mean of 702 CFU/100 mL exiting the
pond. However, occasional high (CFU > 3000/100 mL) fecal coliform counts leaving
18
the pond led to a finding of no statistical difference entering or leaving the pond. The
presence of a number of dumpsters surrounding the site, and consequent small
mammals 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
this large regional pond were low to moderate, and there was a significant reduction in
turbidity (Table 4.1). Fecal coliform concentrations entering Ann McCrary Pond at
BMC-AP1 were very high, however (Table 4.1), possibly a result of pet waste runoff
from the apartment complex and runoff from urban upstream areas. Five of seven
samples collected in 2006 at BMC-AP1 had counts exceeding 200 CFU/100 mL; and
five of seven samples from BMC-AP3 exceeded the standard. There were minor algal
blooms at BMC-AP1 in June and August, and two minor algal blooms (chlorophyll a >
20 µg/L) at BMC-AP3. The efficiency of Ann McCrary Pond as a pollutant removal
device was mixed in 2006. Fecal coliforms were not significantly reduced during
passage through the pond (Table 4.1). As mentioned, turbidity was low and there was
a significant difference in removal of this parameter. In terms of nutrients neither
ammonium, total nitrogen, nor orthophosphate were significantly reduced during
passage through the pond in 2006 (Table 4.1). However, nitrate was significantly
reduced but total phosphorus was significantly increased. 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 phosphorus 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 sampling
period (Appendix B). Dissolved oxygen was substandard (between 2.0 and 5.0 mg/L)
two of seven 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.
Four algal blooms (chlorophyll a exceeding 30 µg/L) occurred at Wallace Park, and two
excessively high algal blooms (exceeding 65 µg/L) occurred at Princess Place in May
and August.
An important issue, from a public health perspective, was the excessive fecal coliform
counts, which maintained geometric means (707 CFU/100 mL at BMC-WP and 294
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 six of
seven months at Wallace Park and four of seven months at Princess Place,
respectively. It is notable that fecal coliform bacteria increased along the passage from
BMC-AP3 to the Wallace Park location, while dissolved oxygen decreased (Table 4.1).
BOD5 analyses were performed at Wallace Park, with median concentrations (2.3
19
mg/L) higher than rural streams but typical of urban streams in the Wilmington area
(Mallin et al. 2006).
In addition to the regular UNCW monitoring effort, the City conducted additional
sampling in September 2006 following the heavy rains associated with Tropical Storm
Ernesto. Fecal coliform bacteria counts in Burnt Mill Creek ranged from 1,500 to 9,300
CFU/100 mL on September 5 and from 1,400 to 11,100 CFU/100 mL on September 6
(reported by Pam Ellis, City of Wilmington). The sources were unclear, but may have
resulted from sewage overflows due to localized flooding. The regular UNCW
sampling on September 13 showed fecal coliform bacteria counts in lower Burnt Mill
Creek ranging from 800 to 1,300 CFU/100 mL, not unusual in comparison with normal
counts in that area.
Table 4.1. Mean and (standard deviation) of water quality parameters in upper Burnt
Mill Creek, Jan. – Sep. 2006. Fecal coliforms as geometric mean; N/P as median.
_____________________________________________________________________
Parameter
KA-1
KA-3
BMC-AP1
BMC-AP3
_____________________________________________________________________
DO (mg/L)
5.3 (2.6)
6.2 (2.4)
6.6 (2.1)
10.4 (1.8)*
Cond. (µS/cm)
340 (124)
309 (101)
255 (63)
239 (25)
pH
6.9 (0.2)
7.0 (0.1)
7.0 (0.2)
8.1 (0.5)*
Turbidity (NTU)
60 (143)
11 (13)
8 (3)
4 (2)*
TSS (mg/L)
10.0 (8.7)
8.7 (7.0)
9.3 (7.7)
7.0 (2.2)
Nitrate (mg/L)
0.084 (0.036) 0.035 (0.040)* 0.078 (0.045) 0.023 (0.016)*
Ammonium (mg/L) 0.130 (0.061) 0.053 (0.057) 0.042 (0.029) 0.072 (0.098)
TN (mg/L)
0.936 (0.296) 0.750 (0.558) 0.916 (0.564) 0.887 (0.210)
OrthoPhos. (mg/L) 0.117 (0.241) 0.017 (0.010) 0.010 (0.000) 0.010 (0.000)
TP (mg/L)
0.207 (0.363) 0.054 (0.019) 0.039 (0.012) 0.080 (0.050)*
N/P molar ratio
18.5
5.1
35.4
14.0
Chlor. a (µg/L)
4.7 (3.3)
8.2 (8.4)
9.8 (12.6)9.7 (7.3)
Fec. col. (/100 mL) 1382
702
564
183
BOD5
3.1 (2.8)
1.6 (0.7)
NA
NA
_____________________________________________________________________
* Indicates statistically significant difference between inflow and outflow at p<0.05
NA = not analyzed. Italics indicate near-significant difference (p < 0.10).
20
Table 4.2. Mean and (standard deviation) of water quality parameters in lower Burnt
Mill Creek, Jan. – Sep. 2006. Fecal coliforms as geometric mean; N/P as median.
_____________________________________________________________________
Parameter
BMC-WP
BMC-PP
_____________________________________________________________________
DO (mg/L)
6.0 (2.6)
5.5 (2.8)
Cond. (µS/cm)
361 (73)
391 (96)
pH
7.3 (0.1)
7.3 (0.1)
Turbidity (NTU)
8 (7)
8 (10)
TSS (mg/L)
6.7 (2.9)
6.9 (3.8)
Nitrate (mg/L)
0.098 (0.045)
0.085 (0.039)
Ammonium (mg/L)
0.047 (0.032)0.051 (0.036)
TN (mg/L)
0.951 (0.358)
0.869 (0.265)
OrthoPhos. (mg/L)
0.030 (0.020)
0.034 (0.025)
TP (mg/L)
0.075 (0.043)
0.106 (0.055)
N/P molar ratio
10.6
7.8
Chlor. a (µg/L)
23.3 (14.3)
35.2 (39.7)
Fec. col. (/100 mL)
707
294
BOD5
2.3 (1.2)
NA
_____________________________________________________________________
NA = not analyzed
21
Figure 4.1. Burnt Mill Creek watershed and sampling sites.
22
Sediment Metals and PAH Concentrations
As part of the stream restoration effort funded through NCSU and the 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
_____________________________________________________________________
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).
23
Most of the stations had sediment metals concentrations that were well below levels
considered potentially toxic to benthic organisms. One exception was lead, which
exceeded the ERL (Table 4.3) at the Wallace Park station BMC-WP and the Princess
Place station (BMC-PP) (Table 4.4). Lead concentrations at BMC-KA1 approached
harmful concentrations but did not exceed them. Copper exceeded the ERL at KA-1
but was much reduced at the output station KA-3; copper concentrations were close to
the ERL at BMC-WP and AP-3 (Table 4.4). Additionally, while not exceeding the ERL
both cadmium and zinc approached it at BMC-WP. All of the PAH sediment samples
exceeded the ERM except for Station AP3, below Ann McCrary Pond, where PAHs
were below the detection limit (Table 4.4). Sediment metals and PAH concentrations in
general were similar to those of 2005 except for the increased copper at KA1 and lead
at BMC-WP and BMC-PP (Mallin et al. 2006). Compared with sediment samples taken
in 1999 at BC-PP, there was a decrease in copper, chromium, lead, and zinc in 2006
(Mallin et al. 1999). This may have been a result of burial of contaminated sediments
by further sedimentation, or flushing from subsequent storm-induced flooding.
Table 4.4. Concentrations of sediment metals and polycyclic aromatic hydrocarbons
(PAHs) in Burnt Mill Creek, 2006 (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 <0.040
<0.040
<0.040
<0.003
<0.050
0.110
Arsenic
<0.020
<0.030
<0.020
<0.020
<0.030
<0.030
Beryllium
0.070
0.050
<0.010
0.058
0.210
0.110
Cadmium
0.170
0.160
<0.010
<0.010
0.870
0.290
Chromium 2.630
3.050
<0.060
3.360
9.940
4.640
Copper
93.00
7.65
0.660
28.60
20.80
8.88
Lead
38.20
19.40
1.600
2.57
150.00
52.90
Mercury
0.047
0.045
0.031
<0.0002
0.051
0.060
Nickel
1.700
1.740
0.100
7.080
3.240
2.130
Selenium <0.060
<0.070
<0.060
0.022
<0.080
<0.080
Silver
<0.010
<0.010
<0.010
<0.010
<0.020
<0.020
Thallium <0.010
<0.010
<0.010
0.011
0.050
<0.030
Zinc
51.60
71.20
4.19
39.30
122.00
68.40
Total PAH 13,981
17,661
889
BDL
3,669
341
TN
214
741
201
700
2,080
1,140
TP
182.0
166.0
18.8
55.0
222.0
381.0
TOC
240.0
106.0
44.0
118.0
75.2
66.2
_____________________________________________________________________
BDL = below detection limit
24
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 2005-2006, there were three incidences of
creek stations having turbidity levels exceeding the state standard of 25 NTU, two of
them at FC-17 (Table 5.1). Low dissolved oxygen was a moderate problem particularly
in the middle creek stations FC-8 and FC-13 (Table 5.1; Appendix B).
Table 5.1. Physical parameters at Futch Creek sampling stations, August 2005 - July
2006. Data given as mean (SD) / range.
_____________________________________________________________________
Station
Salinity
Turbidity
Light attenuation Dissolved oxygen
(ppt)
(NTU)
(k/m)
(mg/L)
_____________________________________________________________________
FC-4
32.1 (3.0)
23.6-35.9
5 (2)
1-8
0.9 (0.4)
0.5-1.3
7.4 (1.8)
4.3-10.1
FC-6
31.3 (3.5)
21.6-35.6
6 (4)
1-15
1.1 (0.5)
0.4-1.7
7.4 (1.9)
4.0-10.1
FC-8
29.5 (4.2)
19.0-34.9
7 (4)
1-14
1.0 (0.4)
0.4-1.3
6.6 (2.2)
3.2-9.7
FC-13
25.2 (4.2)
14.4-30.3
10 (9)
1-35
1.5 (0.5)
0.6-1.9
6.9 (2.3)
2.9-9.2
FC-17
14.0 (9.8)
0.2-26.4
13 (13)
2-50
1.8 (0.4)
1.2-2.2
7.2 (2.7)
2.6-11.9
FOY
22.7 (7.9)
7 (5)
1.1 (0.4)
7.2 (2.4)
1.2-31.0
1-19
0.5-1.5
3.1-10.5
_____________________________________________________________________
Nutrient concentrations in Futch Creek remained generally low, with a general increase
in nitrate over the previous year at all stations (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).
Overland runoff during and following rain events is another nitrate source to this creek.
The creek was free from algal blooms during our sampling visits (Table 5.2), even in the
upper stations.
Table 5.2. Nutrient and chlorophyll a data from Futch Creek, August 2005-July 2006.
Data as mean (SD) / range, nutrients in mg/L, chlorophyll a as µg/L.
25
_____________________________________________________________________
Station
Nitrate
Ammonium
Orthophosphate
Chlorophyll a
_____________________________________________________________________
FC-4
FC-6
FC-8
FC-13
FC-17
0.020 (0.032)0.017 (0.013)0.011 (0.005)2.1 (1.6)
0.003-0.110
0.001-0.041
0.006-0.021
0.6-4.8
0.022 (0.035)
0.002-0.124
NA
0.011 (0.005)2.7 (2.1)
0.005-0.025
1.0-6.3
0.026 (0.029)
0.005-0.105
NA
0.011 (0.005)3.0 (2.6)
0.004-0.021
0.7-6.9
0.042 (0.029)
0.010-0.096
NA
0.011 (0.004)4.2 (3.8)
0.006-0.018
1.1-10.2
0.069 (0.051)0.032 (0.034)0.012 (0.004)5.5 (4.5)
0.015-0.179
0.001-0.115
0.006-0.019
1.2-14.9
FOY
0.049 (0.039)0.029 (0.030)0.011 (0.005)3.6 (2.4)
0.013-0.133
0.001-0.117
0.006-0.019
1.1-7.3
_____________________________________________________________________
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
2005-2006 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, but one station (FC-17) had five
out of 12 incidents of fecal coliform counts exceeding 200 CFU/mL. There was a
decline in microbiological water quality at the upper stations compared with the previous
year (Fig. 5.2), yielding a poor rating (Appendix B). It is troublesome that two of the
past three years showed decreases in water quality in upper Futch Creek.
Nevertheless, all stations had geometric mean fecal coliform counts that were within
safe limits for human contact waters (Appendix B). In summary, Futch Creek still
maintains good water quality in general, but it appears to be showing signs of
degradation (Appendix B).
26
Figure 5.1. Futch Creek watershed and sampling sites.
27
Table 5.3. Futch Creek fecal coliform bacteria data, including percent of samples
exceeding 43 CFU per 100 mL, August 2005 - July 2006.
_____________________________________________________________________
Station
FC-4 FC-6 FC-8 FC-13 FC-17 FOY
Geomean (CFU/100 mL)
2
12
9
29
116
24
% > 43 /100ml
9
9
9
25
67
33
_____________________________________________________________________
Figure 5.2 Fecal coliform bacteria counts over time at selected
Futch Creek stations, 1994-2006
250
Fecal coliforms
(CFU/100mL)
Channel dredging in
mouth of creek
200
150
100
50
0
1994
1
1995
2
1996
3
1997
4
FC8
1998
5
1999
6
2000
7
Year
FC13
2001
8
FC17
2002
9
2003
10
FOY
2004
11
200512
28
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 GLJRB (Jumping Run Branch), GL-LB (creek at Lake Branch Drive) and GL-LC (creek
beside Lakeshore Commons) all showing average concentrations below the state
standard (DO < 5.0 mg/L). Dissolved oxygen levels were 2.0 mg/L or less on six
occasions at GL-LB and twice each at the other two stations (Table 6.1; Appendix B).
Turbidity and suspended solids were generally low in the tributary stations except for
high turbidity at GL-JRB and GL-LC in August 2006 (Table 6.1). Total nitrogen and
nitrate concentrations were highest at GL-LC and GL-LB, and lowest at GL-JRB
(Jumping Run Branch) (Table 6.1). Ammonium concentrations were highest at GL-LB,
followed by GL-LC. 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) six of seven times at GL-LB, and GL-LC, and five of seven
times at GL-JRB. Geometric mean fecal coliform bacteria concentrations were very
high at all three sites, with values of 417, 813, and 818 at GL-JRB, GL-LB and GL-LC,
respectively - a decrease in water quality from the previous year. There was one major
algal bloom in June at GL-LC, with a chlorophyll a level of 58 µg/L. Lesser blooms of
18 and 22 µg/L occurred at GL-JRB, and GL-LC was free from blooms in 2006.
Table 6.1. Mean and (standard deviation) of water quality parameters in tributary
stations of Greenfield Lake, January - September 2006. Fecal coliforms as geometric
mean; N/P ratio as median; n = 7 samples for all parameters.
_____________________________________________________________________
Parameter
GL-JRB
GL-LB
GL-LC
_____________________________________________________________________
DO (mg/L)
4.0 (2.3)
1.9 (2.0)
3.3 (1.9)
Turbidity (NTU)
3(1)
3 (1)
20 (40)
TSS (mg/L)
6.6 (9.9)
3.9 (3.2)
19.0 (41.9)
Nitrate (mg/L)
0.079 (0.057)0.141 (0.108)0.279 (0.179)
Ammonium (mg/L)
0.080 (0.037)
0.253 (0.104)0.170 (0.112)
TN (mg/L)
0.760 (0.225)
1.163 (0.404)1.110 (0.319)
Orthophosphate (mg/L)
0.044 (0.021)
0.049 (0.023)0.053 (0.070)
TP (mg/L)
0.106 (0.087)
0.127 (0.078)0.110 (0.124)
N/P molar ratio
6.1
18.3
42.1
Fec. col. (/100 mL)
417
813
818
Chlor. a (µg/L)
8.2 (8.7)
4.4 (2.3)
13.4 (19.8)
BOD5
1.5 (0.4)
1.3 (0.4)
1.5 (1.3)
_____________________________________________________________________
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 2003 and 2004
(see Section 6.1). Turbidity and suspended solids were low to moderate at these three
29
sites, except for high TSS (72 mg/L) in February at GL-2340. Fecal coliform
concentrations were only problematic at GL-2340 (Appendix B) with four of seven
samples exceeding the State standard in 2006.
Nitrogen concentrations were generally highest at GL-P, followed by GL-2340, while
phosphorus concentrations were highest at GL-YD, and none of the nutrient values
were remarkable (Table 6.2). 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).
One fish kill was reported in Greenfield Lake in 2006. On February 13 UNCW
researchers were called by City staff who reported that 82 dead fish had been found.
The following day UNCW researchers visited the site and found 17 carcasses
remaining, with acceptable dissolved oxygen concentrations (> 7.0 mg/L). The cause of
the kill was thus unknown.
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. Two
major and one minor algal bloom occurred at GL-P, four major blooms occurred at GL2340, and two major and one minor bloom occurred at GL-YD. The magnitude of the
major in-lake blooms ranged from 44-210 µg/L of chlorophyll a. The eight algal blooms
exceeding the state standard of 40 µg/L were a slight 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 2006 Greenfield Lake was impaired by algal
blooms, high fecal coliform counts and low dissolved oxygen concentrations, although
the latter parameter continues to be better than the 2003-2004 period. 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; 2006).
30
Table 6.2. Mean and (standard deviation) of water quality parameters in Greenfield
Lake sampling stations, January - September 2006. 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)
4.9 (2.6)
8.4 (3.8)
10.0 (3.7)
Turbidity (NTU)
1 (1)
2 (2)
3 (1)
TSS (mg/L)
13.0 (26.1)
4.7 (3.3)
4.4 (2.5)
Nitrate (mg/L)
0.066 (0.044)0.020 (0.008)0.056 (0.091)
Ammonium (mg/L)
0.029 (0.025)
0.019 (0.023)0.033 (0.024)
TN (mg/L)
0.893 (0.346)
1.063 (0.417)1.061 (0.361)
OrthopPhosphate (mg/L) 0.020 (0.014)
0.023 (0.034)0.039 (0.063)
TP (mg/L)
0.070 (0.041)
0.084 (0.045)0.091 (0.069)
N/P molar ratio
12.2
7.3
7.3
Fec. col. (/100 mL)
185
44
52
60.9 (73.4)
27.1 (23.9)
30.5 (25.3)
Chlor. a (µg/L)
BOD5
3.3 (2.0)
3.9 (2.2)
3.8 (1.9)
____________________________________________________________________
31
32
6.1 A Continuing Assessment of the Efficacy of the 2005-2006 Greenfield Lake
Restoration Measures
Michael A. Mallin and Brad Rosov
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 2005 a contract firm applied the herbicide Sonar to further reduce
the amount of aquatic macrophytes. On March 29-31 2006 City crews applied 35
gallons of K-Tea algaecide and on July 18 applied 0.63 gallons of habitat aquatic
herbicide. A contract firm stocked the lake with 500 additional grass carp on April 4,
2006 and applied 40 gallons of Nautique aquatic herbicide on April 25.
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
33
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
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
the summers of 2005 and 2006 (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 (DO): 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
(DO of zero) or nearly so, especially at GL-P, the main Park area (Fig. 6.1). Following
the onset of herbicide addition in April 2005, the May DO (mean of the three in-lake
stations) 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 of
2005 (Fig. 6.2). In summer of 2006 the average lake DO levels decreased compared
with 2005, but were still higher than in 2003 and 2004 (Fig. 6.2). This was because
Station GL-2340 experienced low DO levels from 1.2 to 3.8 mg/L from July through
September, although the other two in-lake stations (GL-P and GL-YD) maintained good
DO levels (Table 6.2).
Turbidity: Turbidity was not excessive in the lake during the two years prior to
restoration efforts (Mallin et al. 2006). It has remained low following these efforts
throughout 2005 (Mallin et al. 2006) and 2006 (Table 6.2).
Ammonium: Ammonia, or 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 has not raised ammonium concentrations in the lake (Fig.
6.3). 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 (Table 6.2).
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 (Table 6.2; Fig. 6.4).
Orthophosphate: Orthophosphate is the most common inorganic form of phosphorus,
and is utilized as a key nutrient by aquatic macrophytes and phytoplankton.
34
Orthophosphate was not found at excessive concentrations in the water column either
before (Mallin et al. 2006) or after the restoration effort (Table 6.2).
Total phosphorus: Total phosphorus (TP) is a combination of all organic and inorganic
forms of phosphorus in the water. Although pulses of TP occurred in summer 2005 and
spring 2006, they were similar in magnitude to pulses of TP seen in 2003 and 2004
(Fig. 6.5), so the restoration efforts do not seem to have impacted TP levels in the lake.
Chlorophyll a: Chlorophyll a is the principal measure used to estimate phytoplankton
biomass (algal bloom strength) in water bodies. As mentioned above, algal blooms
have been a common occurrence in this lake. They are generally patchy in space,
usually occurring at one or two stations at a time. 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 (Fig. 6.6). Blooms have continued throughout 2006 as
well (Table 6.2; Fig. 6.6). Algal blooms are the result of nutrient inputs, either from
outside the lake or from release from decaying material. Algal blooms, when they die,
cause a BOD (biochemical oxygen demand) load. This is organic material that natural
lake bacteria feed on and multiply, using up dissolved oxygen in the lake as they do so.
We compared our 2006 chlorophyll a concentrations with the corresponding BOD
concentrations for the three in-lake stations. The results (Fig. 6.7) show a highly
statistically significant relationship between the chlorophyll a levels and BOD.
Statistically speaking, the regression equation on Fig. 6.7 means that approximately
55% of the variability in Greenfield Lake BOD is caused by algal blooms. These
blooms thus can lead to low dissolved oxygen in the lake. Some of the lowest DO
readings at Station GL-2340 occurred during some of the densest algal blooms in
summer 2006.
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 during several months (Table 6.2; Fig. 6.8). 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. 6.8). Excessive fecal
coliform counts occurred to a lesser degree in 2006 in the lake, mainly at GL-2340
(Table 6.2).
35
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. As mentioned above, this would serve to drive the lake DO
concentrations downward. DO levels in summer 2005 were nearly twice what they
were during summers of 2003 and 2004, and DO levels in 2006 were also higher than
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. The in-lake
station with lowest DO levels in 2006 was GL-2340, which is located quite a distance
from the SolarBees.
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 2005 and 2006. 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. As mentioned, a
problem with algal blooms is that when they die, they become labile forms of organic
material, or BOD (Fig. 6.7). Published research has previously demonstrated that
chlorophyll a in this lake is strongly correlated with BOD (Mallin et al. 2005).
The continuing problems with 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, or feral cats could lead to increased fecal coliform
bacteria counts, but we have no data to support this speculation either way.
References Cited
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.
36
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., L.B. Cahoon, M.H. Posey, V.L. Johnson, D.C. Parsons, T.D. Alphin, B.R.
Toothman, M.L. Ortwine and J.F. Merritt. 2006. Environmental Quality of Wilmington
and New Hanover County Watersheds, 2004-2005. CMS Report 06-01, 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.
13
12
11
10
9
8
7
6
5
4
3
2
1
0
NC standard 5.0 m g/L
2004
2005
p
Se
l
Ju
M
ay
b
Fe
A
ug
Ju
ar
M
p
Se
l
Ju
M
ay
n
Ja
A
ug
b
n
Ju
2003
n
April 2005
Addition of herbicides
Addition of aerators and
grass carp, February 2005
Fe
Dissolved oxygen (mg/L)
Figure 6.2. Average dissolved oxygen concentrations in
Greenfield Lake, 2003-2006.
2006
37
Figure 6.3. Average ammonium concentrations for
Greenfield Lake, 2003-2006
Ammonium (mg-N/L)
0.7
0.6
0.5
0.4
Addition of aerators and
grass carp, February 2005
0.3
April 2005
Addition of
herbicides
0.2
0.1
2003
2004
2005
Se
p
l
Ju
M
ay
b
Fe
A
ug
n
Ju
ar
M
p
Se
l
Ju
M
ay
n
Ja
A
ug
n
Ju
Fe
b
0.0
2006
Figure 6.4. Average total nitrogen (TN) concentrations in
Greenfield Lake, 2003-2006
2.5
TN (mg-N/L)
2.0
1.5
1.0
April 2005, Addition
Addition of aerators and
of herbicides
grass carp, February 2005
0.5
0.0
b
Fe
n
Ju
2003
g
Au
n
Ja
ay
M
2004
l
Ju
p
Se
M
ar
n
Ju
2005
g
Au
b
Fe
ay
M
l
Ju
p
Se
2006
38
Figure 6.5. Average total phosphorus (TP) concentrations for
Greenfield Lake, 2003-2006
0.25
TP (mg-P/L )
0.20
0.15
0.10
0.05
2003
2004
2005
p
l
Se
Ju
M
ay
b
Fe
A
ug
n
Ju
M
ar
p
Se
l
Ju
M
ay
n
Ja
A
ug
n
Ju
Fe
b
0.00
2006
Figure 6.6. Average chlorophyll a values in
Greenfield Lake, 2003-2006
Addition of aerators
and grass carp,
February 2005
100
80
Addition of
herbicides,
April 2005
60
NC standard 40 µ g/L
40
20
2003
2004
2005
2006
p
Se
l
Ju
ay
M
b
Fe
A
ug
n
Ju
ar
M
p
Se
l
Ju
ay
M
n
Ja
A
ug
n
Ju
b
0
Fe
Chlorophyll a (µ g/L)
120
39
Figure 6.7. BOD5 as a function of chlorophyll a in Greenfield Lake, 2006
(data from all three in-lake stations combined).
9.0
8.0
BOD5 (mg/L)
7.0
6.0
5.0
4.0
3.0
y = 0.0506x + 2.2556
R2 = 0.5517
p = 0.001
2.0
1.0
0.0
0
10
20
30
40
50
60
70
80
90
100
Chlorophyll a (µ g/L)
Figure 6.8. Average fecal coliform bacteria counts (FC) for
Greenfield Lake, 2003-2005
1800
1400
1200
1000
NC recreational
w aters fecal
coliform standard
800
600
400
200
2003
2004
2005
p
Se
l
Ju
M
ay
b
Fe
A
ug
n
Ju
ar
M
p
Se
l
Ju
M
ay
n
Ja
A
ug
n
Ju
b
0
Fe
FC (CFU/100 mL)
1600
2006
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 20052006 sampling; three at NB-GLR and five at SB-PGR. 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
three minor algal blooms at NB-GLR in February, April and July (25, 19, and 31 µg/L of
chlorophyll a respectively) and additional one of 21 µg/L of chlorophyll a was seen at
SB-PGR in February 2006. Algal blooms have been common in upper Hewletts Creek
in the past (Mallin et al. 1998a; 1999; 2002a; 2004; 2005). Monthly fecal coliform
bacteria samples were not collected in the tidal areas of the creek in 2005-2006.
However, a special sampling was necessitated when a substantial sewage leak
occurred in the watershed of the middle branch of the creek on or about February 27,
2006. On that day fecal coliform counts were 20,000 CFU/100 mL at MB-PGR;
subsequent samples on March 2 found counts of 4,000, 2,580 and 2,200 at NB-GLR,
MB-PGR and SB-PGR, respectively, with counts of 41 CFU/100 ML at HC-NWB and 4
CFU/100 Ml at HC-M.
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 increased over the
previous year (2004-5) study (Mallin et al. 2006). Fecal coliform bacteria counts
exceeded State standards five out of seven times in 2006 at PVGC-9. An earlier
assessment (Mallin and Wheeler 2000) noted higher fecal coliform counts entering the
course from suburban neighborhoods upstream than counts at PVGC-9 leaving the
course.
41
Table 7.1. Selected water quality parameters at lower and middle creek stations in
Hewletts Creek watershed as mean (standard deviation) / range, August 2005-July
2006. Fecal coliform bacteria presented as geometric mean / range.
_____________________________________________________________________
Parameter
HC-2
HC-3
_____________________________________________________________________
Salinity
(ppt)
32.9 (1.2)
31.0-34.9
30.6 (2.3)
26.3-33.7
Turbidity
(NTU)
5 (3)
1-12
5 (2)
1-8
DO
(mg/L)
7.4 (1.6)
5.6-10.5
7.1 (1.9)
5.2-10.6
Nitrate
(mg/L)
0.015 (0.013)
0.032 (0.061)
0.003-0.036
0.003-0.220
Ammonium
(mg/L)
0.011 (0.012)NA
0.001-0.045
Orthophosphate
(mg/L)
0.008 (0.004)
0.003-0.017
0.010 (0.008)
0.004-0.026
Mean N/P
Median
6.9
6.0
NA
Light attenuation
(K/m)
0.6 (0.2)
0.4-0.8
1.0 (0.4)
0.5-1.3
Chlorophyll a
(µg/L)
1.9 (0.7)
0.7-2.9
2.1 (1.3)
0.8-5.7
Fecal col.
NA
NA
CFU/100 mL
_____________________________________________________________________
NA = not analyzed
42
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 2005-July 2006; for PVGC-9, n = 6 months.
_____________________________________________________________________
Parameter
NB-GLR
SB-PGR
MB-PGR
PVGC-9
_____________________________________________________________________
Salinity
(ppt)
12.6 (8.6)
0.5-25.7
18.2 (7.7)
1.3-27.6
0.2 (0.2)
0.1-0.9
0.1 (0.0)
0.1-0.1
Turbidity
(NTU)
9 (5)
3-21
8 (3)
3-12
4 (3)
0-8
2 (2)
0-4
DO
(mg/L)
6.6 (1.9)
3.9-9.6
6.4 (2.1)
4.2-10.1
7.0 (0.9)
5.0-8.3
6.1 (1.3)
4.1-8.2
Nitrate
(mg/L)
0.099 (0.075) 0.061 (0.032)
0.259 (0.117)
0.410 (0.195)
0.022-0.303 0.020-0.125
0.033-0.438
0.140-0.670
0.043 (0.015)
0.020-0.060
Ammonium
(mg/L)
0.175 (0.310) 0.078 (0.079)
0.016-0.1118 0.001-0.286
0.119 (0.097)
0.024-0.343
Orthophosphate
(mg/L)
0.019 (0.013) 0.020 (0.012)
0.009-0.045 0.008-0.045
0.022 (0.012)0.011 (0.004)
0.011-0.053
0.010-0.020
Mean N/P ratio
Median
28.7
25.6
19.1
20.3
40.7
41.8
92.7
104.1
Light attenuation
(K/m)
NA
NA
NA
NA
Chlor a
(µg/L)
9.8 (10.5)
1.1-31.3
5.3 (5.9)
0.8-20.7
0.9 (0.5)
0.1-1.8
2.2 (1.6)
0.5-5.3
Fecal coliforms
NA
NA
NA
530
CFU/100 mL
120-3200
_____________________________________________________________________
NA = not analyzed
Dobo Property: 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
43
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.
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 2006. n = 7.
_____________________________________________________________________
Parameter
DB-1
DB-2
DB-3
DB-4
_____________________________________________________________________
Turbidity
(NTU)
7 (8)
1-21
3 (2)
0-5
7 (3)
4-11
9 (5)
6-20
TSS
mg/L
13.7 (13.2)
2-39
8.0 (11.6)
2-34
4.2 (2.7)
1-9
3.9 (1.3)
3-6
DO
(mg/L)
3.2 (2.0)
1.2-6.2
5.5 (1.7)
3.3-8.8
6.4 (0.9)
5.2-8.0
6.6 (1.4)
4.4-9.1
Nitrate
(mg/L)
0.062 (0.044) 0.033 (0.026)
0.111 (0.097)
0.124 (0.061)
0.013-0.120 0.013-0.070
0.010-0.310
0.050-0.230
Ammonium
(mg/L)
0.812 (0.634) 0.174 (0.104)
0.060-1.920 0.040-0.2330
0.199 (0.040)
0.140-0.260
TN
(mg/L)
1.973 (0.609) 1.031 (0.800)
1.100-2.850 0.330-1.970
1.096 (0.426)1.014 (0.251)
0.670-1.730
0.760-1.530
Orthophosphate
(mg/L)
0.103 (0.064) 0.016 (0.011)
0.010-0.190 0.010-0.040
0.041 (0.019)0.026 (0.013)
0.010-0.070
0.010-0.040
TP
(mg/L)
0.134 (0.067) 0.049 (0.007)
0.040-0.210 0.040-0.060
0.061 (0.023)0.050 (0.018)
0.040-0.090
0.020-0.070
Chlor a
(µg/L)
4.1 (3.6)
0.5-11.1
0.3 (0.2)
0.2-0.6
4.9 (4.6)
1.0-14.2
0.139 (0.059)
0.060-0.220
2.0 (2.6)
0.5-7.9
Fecal coliforms
917
590
395
794
CFU/100 mL
360-917
200-590
36-2900
185-2700
_____________________________________________________________________
In 2006 all nutrient species except nitrate 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 (particularly ammonium), showing that the property already has some
function in water quality improvement. The exception was nitrate, which showed an
increase at DB-4 compared with DB-1. Dissolved oxygen was particularly low only at at
44
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 high at all sites, particularly DB-1 and DB-4 (Table 7.3). The data suggest
that fecal coliform bacteria and nitrogen should be targeted in particular for removal by
the treatment facility.
45
46
47
8.0 Howe Creek Water Quality
Howe Creek was sampled for physical parameters, nutrients, chlorophyll a , and fecal
coliform bacteria at five locations during 2005-2006 (HW-M, HW-FP, HW-GC, HW-GP
and HW-DT- Fig. 8.1). Turbidity was low near the ICW but did exceed the North
Carolina water quality standard of 25 NTU at HW-DT(the uppermost station) in January
2006, and was close to the standard with 24 NTU in July 2006 at HW-GP (Table 8.1;
Appendix B). Dissolved oxygen concentrations were good to fair in Howe Creek, with
HW-GC, HW-GP and HW-DT each below the standard of 5.0 mg/L on two occasions
(Appendix B). Nitrate concentrations were low at the lower stations but increased
upstream, and were approximately double those of the 2004-2005 period (Table 8.2).
Median inorganic molar N/P ratios were low, reflecting low nitrate levels, and indicating
that nitrogen was probably the principal nutrient limiting phytoplankton growth at all
stations. There was one major algal bloom of 61 µg/L as chlorophyll a at HW-DT and a
minor bloom of 24 µg/L at HW-GP. Since wetland enhancement was performed in
1998 above Graham Pond the creek below the pond at HW-GP has had fewer and
smaller algal blooms than before the enhancement (Fig. 8.2). Light attenuation showed
generally clear water except for elevated readings > 3.0/m at the upper stations in
January and April 2006.
Table 8.1. Water quality summary statistics for Howe Creek, August 2005-July 2006,
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 (1.1)
31.8-34.6
7.2 (1.7)
5.3-10.8
4 (1)
2-7
0.7 (0.3)
0.4-1.2
2.5 (1.8)
0.4-5.9
3
1-52
HW-FP
33.1 (1.3)
31.3-34.6
7.2 (1.8)
5.1-10.9
4 (1)
2-5
0.5 (0.2)
0.4-0.8
2.2 (1.7)
0.5-6.0
4
0-90
HW-GC
30.2 (2.8)
22.4-34.0
7.0 (2.0)
4.3-10.8
6 (3)
4-15
1.6 (1.2)
0.7-3.3
3.1 (3.2)
0.7-11.8
27
5-393
HW-GP
13.7 (11.7)
106-33.0
6.9 (1.9)
4.4-9.7
10 (7)
2-24
2.8 (1.6)
1.3-4.5
7.9 (7.2)
1.1-23.7
190
31-4075
HW-DT
4.0 (6.8)
0.1-23.7
7.4 (1.9)
4.4-10.0
3.3 (1.2)
2.4-4.1
9.5 (16.6)
1.3-61.2
265
41-3025
12 (9)
3-39
48
Figure 8.1. Howe Creek watershed and sampling sites.
49
Fig. 8.2. Chlorophyll a concentrations (algal blooms) in Howe Creek below Graham Pond
before and after 1998 wetland enhancement in upper Graham Pond.
100
90
wetland
enhancement
Chlorophyll a (ppb)
80
70
60
NC chlorophyll a standard for impaired waters
50
40
30
20
10
0
t
t
t
t
t
t y
t
t
t
t
t
t
t
y
y
y
y
y
y
y
y
y
y
y
y
us ar us ar us ar us ar us ar us ar us ar us ar us ar us ar us ar us ar us ar
ug bru ug bru ug bru ug bru ug bru ug bru ug bru ug bru ug bru ug bru ug bru ug bru ug bru
A e
A e
A e
A e
A e
A e
A e
A e
A e
A e
A e
A e
A e
F
F
F
F
F
F
F
F
F
F
F
F
F
1993 1994 1995
1996 1997 1998 1999
2000
2001
2002
2003
2004 2005 2006
Table 8.2. Nutrient concentration summary statistics for Howe Creek, August 2005-July
2006, 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
0.013 (0.020)0.008 (0.006)0.008 (0.005)
5.5
0.002-0.058
0.001-0.018
0.004-0.020
4.6
0.008 (0.005)0.010 (0.005)0.008 (0.002)
4.8
0.002-0.021
0.001-0.020
0.005-0.011
4.3
HW-GC
0.014 (0.013)
0.005-0.048
HW-GP
0.033 (0.031)0.032 (0.021)0.013 (0.007)
12.5
0.007-0.093
0.006-0.065
0.005-0.034
HW-DT
NA
0.009 (0.004)
0.004-0.018
NA
10.9
0.060 (0.038)0.033 (0.018)0.014 (0.007)20.0
0.004-0.127
0.008-0.060
0.004-0.031
12.1
____________________________________________________________________
NA = not analyzed
50
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 six of 12 occasions, and
HW-DT also exceeded the standard on six of 12 occasions (Appendix B). The 20052006 data show a worsening in fecal coliform (mid-creek) counts after somewhat better
bacterial water quality seen in 2004-2005 Howe Creek (Fig. 8.3).
Figure 8.3. Geometric mean fecal coliform bacteria counts for
Howe Creek over time, 1993-2006
600
500
400
300
200
100
0
HW-M
HW-FP
HW-GC
HW-GP
HW-DT
STATION
1993-1994
2003-2004
1996-1997
2004-2005
1999-2000
2005-2006
2001-2002
2002-2003
Mayfaire Town Center drainage special study: Between December 2004 and April 2006
a special student project was undertaken by Amanda Maness, an Earth Sciences
graduate student, focusing on runoff of pollutants from the Mayfaire Town Center. On
six occasions, three wet periods and three dry periods, she sampled fecal coliform
bacteria and turbidity at four sites along or near Military Cutoff where drainage from
Mayfaire could impact Howe Creek. The locations included the main ditch under the
road (MC), a station located near Mayfaire Village further north along Military cutoff
(MV) and two sites near Research Park (MC-RP and MC-RP2). A fifth station on
Eastwood Road (ER) that drains into the north branch of Bradley Creek was also
sampled.
51
Table 8.3. Fecal coliform bacteria and turbidity concentrations in drainages from
Mayfaire Town Center in the upper Howe Creek watershed.
_____________________________________________________________________
Site
Fecal coliforms
Turbidity
Geometric mean and range
Mean + st. deviation and range
_____________________________________________________________________
MC
4 (1-47)
27+30 (3-82)
MV
2 (1-39)
7+3 (4-11)
MC-RP
3 (1-2000)
12+3 (9-15)
MC-RP2
43 (15-124)
6+2 (3-8)
ER
52 (3-1000)
13+8 (3-45)
_____________________________________________________________________
The results (Table 8.3) showed that there was little drainage of those pollutants from
Mayfaire into Howe Creek, even during rainy periods. The North Carolina fecal coliform
human contact standard of 200 CFU/100 mL was only exceeded on one occasion at
one site (May 28, 2005 at MC-RP - 2000 CFU/100 mL) in the Howe Creek drainage.
The two highest fecal coliform counts did not occur during rainfall events. Turbidity only
exceeded the NC freshwater standard of 50 NTU on one occasion (April 8, 2006 at MC
- 82 NTU) into Howe Creek drainage. Apparently the stormwater controls from
Mayfaire are doing a good job of minimizing pollutant runoff under and near Military
Cutoff.
At the Eastwood Road station (ER) the fecal coliform standard was exceeded on one of
six occasions (September 3, 2005 - 1000 CFU/100 mL), and the turbidity standard was
not exceeded. For all sites combined there was no significant statistical relationship
between fecal coliform counts and rainfall, again showing generally good stormwater
runoff control from Mayfaire.
52
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 5.0 mg/L from April through September
(range 3.7-4.8 mg/L) similar to previous years (Mallin et al. 2003; 2004; 2006). 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 657 CFU/100 mL well above the previous two years
and exceeding the State standard of 200 CFU/100 mL on all seven sampling occasions
(Appendix B). Total nitrogen, ammonium, and total phosphorus levels were similar to
the previous year’s study, and chlorophyll a concentrations were not a problem, with no
algal blooms detected in 2006 (Table 9.1). BOD5 was sampled on seven occasions in
2005, yielding a mean value of 1.4 mg/L and a median value of 1.4 mg/L, generally
similar to previous years (Mallin et al. 2003; 2004; 2005; 2006). Thus, this creek
showed mixed water quality, with algal blooms and BOD not problematic, dissolved
oxygen a minor problem and fecal coliform counts steadily getting worse.
53
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 2006. Fecal coliforms as geometric mean / range.
_____________________________________________________________________
Parameter
MOT-RR
Mean (SD)
Range
_____________________________________________________________________
Salinity (ppt)
2.1 (2.5)
0.1-6.2
TSS (mg/L)
11.3 (6.7)
5.0-25.0
Turbidity (NTU)
11 (5)
6-19
DO (mg/L)
5.0 (1.9)
3.7-9.3
Nitrate (mg/L)
0.126 (0.082)
0.040-0.260
Ammonium (mg/L)
0.041 (0.042)
0.005-0.130
Total nitrogen (mg/L)
0.971 (0.179)0.690-1.170
Orthophosphate (mg/L)
0.019 (0.007)0.010-0.030
Total phosphorus (mg/L)
0.056 (0.020)0.030-0.090
Mean N/P ratio
Median
26.5
21.6
Chlor a (µg/L)
8.3 (7.6)
0.6-21.0
BOD5 (mg/L)
1.4 (0.6)
0.9-2.6
Fecal coliforms (CFU/100 mL)
657
270-3500
__________________________________________________________________
54
55
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 several incidents of hypoxia
during summers of 2005 and 2006, three each at the stations draining upper and lower
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 to moderate with
one major algal bloom of 31 µg/L noted at PC-BDUS and one minor bloom of 17 µg/L
noted at PC-BDDS (Table 10.1). Median inorganic nitrogen-to-phosphorus molar ratios
were at or 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.
56
Table 10.1. Selected water quality parameters in Pages Creek as mean (standard
deviation) / range, August 2005-July 2006.
_____________________________________________________________________
Parameter
PC-M
PC-BDDS
PC-BDUS
_____________________________________________________________________
Salinity (ppt)
34.0 (1.3)
31.6-36.2
28.6 (5.5)
14.8-33.9
13.8 (10.0)
3.1-30.8
Turbidity (NTU)
4 (2)
2-8
5 (4)
1-15
8 (7)
3-23
DO (mg/L)
7.4 (2.0)
5.0-11.1
6.6 (2.1)
3.2-10.4
6.5 (2.5)
3.0-10.9
Nitrate (mg/L)
0.017(0.025)
0.002-0.077
0.028(0.020)
0.006-0.070
0.037(0.028)
0.006-0.107
Ammonium (mg/L)
0.012(0.009) 0.026(0.020) 0.078(0.039)
0.001-0.033
0.001-0.057
0.013-0.132
Orthophosphate (mg/L)
0.009(0.007)
0.005-0.027
Mean N/P Ratio
median
5.9
5.2
Chlor a (µg/L)
0.013(0.007)
0.008-0.033
9.7
9.0
0.018(0.012)
0.006-0.050
16.9
14.1
2.1 (1.1)
4.2 (5.0)
7.5 (9.3)
0.3-3.6
0.4-17.8
0.6-31.8
_____________________________________________________________________
57
Figure 10.1. Pages Creek watershed and sampling sites.
58
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 2006. Dissolved oxygen
concentrations were below 5.0 mg/L on three occasions each at SC-23 and SC-CH
between June and September 2006, although the lowest value was 3.4 mg/L, not
excessively stressful to aquatic life. The North Carolina turbidity standard for estuarine
waters (25 NTU) was not exceeded during 2006, similar to last year. Suspended solids
concentrations in Smith Creek were second only to Barnards Creek in the Wilmington
watersheds system.
Nutrient concentrations remained similar to last year's levels (Table 11.1), and one algal
bloom exceeding the State standard was found in 2006, a value of 48 µg/L at SC-23 in
August; A lesser algal bloom of 25 µg/L occurred at SC-23 in May. Fecal coliform
bacteria concentrations were above 200 CFU/100 mL on two occasions each at both
sites, a deterioration from last year (Mallin et al. 2006) 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 2006 at SC-CH, with a mean value of
1.1 mg/L and a median value of 1.2 mg/L, an improvement over last year.
59
Table 11.1. Selected water quality parameters in Smith Creek watershed as mean
(standard deviation) / range. January - September 2006.
_____________________________________________________________________
Parameter
SC-23
SC-CH
Mean (SD) Range
Mean (SD) Range
_____________________________________________________________________
Salinity (ppt)
0.6 (0.7)
0.1-2.0
2.2 (2.6)
0.1-6.6
Dissolved oxygen (mg/L)
5.7 (2.0)
4.0-10.0
5.8 (2.6)
3.4-11.2
Turbidity (NTU)
11 (5)
5-18
13 (3)
9-17
TSS (mg/L)
14.1 (7.4)
6.0-24.0
17.1 (8.0)
12.0-35.0
Nitrate (mg/L)
0.062 (0.050) 0.013-0.140
0.111 (0.092) 0.030-0.280
Ammonium (mg/L)
0.042 (0.049) 0.005-0.150
0.056 (0.041) 0.005-0.140
Total nitrogen (mg/L)
0.941 (0.254) 0.580-1.320
1.039 (0.175) 0.510-1.260
Orthophosphate (mg/L)
0.017 (0.013) 0.010-0.040
0.044 (0.021) 0.010-0.080
Total phosphorus (mg/L)
0.059 (0.030) 0.010-0.090
0.099 (0.046) 0.040-0.160
Mean N/P ratio
Median
13.0
12.2
12.4
8.3
Chlor. a (µg/L)
15.1 (16.4)
0.5-48.0
4.3 (1.9)
1.8-7.0
Fecal col. /100 mL
(geomean / range)
160
44-1200
134
42-460
BOD5 (mg/L)
NA
NA
1.1 (0.4)
0.4-1.6
_____________________________________________________________________
NA = not analyzed
60
61
12.0 Whiskey Creek
Whiskey Creek drains into the ICW. Sampling of this creek began in August 1999.
Five stations were sampled in 2005-2006; 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 three
of 12 occasions each at WC-MLR and WC-AB in 2005-2006 (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 17 µg/L at WC-AB in July 2006;
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, and were similar to 2004-2005 (Mallin et al. 2006).
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 WCMB were highest among all creek mouth stations in the tidal creek system. Fecal
coliform bacteria were not sampled in 2005-2006. 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 2005-July
2006, presented as mean (standard deviation) / range.
Salinity
Dissolved oxygen Turbidity
Chlor a Light attenuation
(ppt)
(mg/L)
(NTU)
(µg/L)
(k/m)
_____________________________________________________________________
WC-MB
29.6 (2.1)
26.0-32.6
7.1 (1.9)
4.5-10.8
5 (3)
2-12
3.0 (2.7)
0.9-10.6
1.0 (0.3)
0.7-1.5
WC-AB
26.0 (4.8)
12.4-30.9
6.9 (2.2)
4.3-10.9
8 (4)
3-14
3.6 (4.5)
0.8-16.7
NA
NA
WC-MLR
22.8 (7.2)
1.3-29.3
6.8 (2.2)
3.5-10.4
8 (4)
2-15
3.5 (3.0)
0.7-9.6
NA
NA
WC-SB
0.2 (030)
0.0-1.0
7.4 (1.0)
5.6-8.9
5 (2)
2-8
0.9 (0.6)
0.1-1.8
NA
NA
WC-NB
0.3 (0.5)
6.6 (1.4)
4 (1)
0.7 (0.9)
NA
0.1-2.0
4.8-8.5
2-7
0.1-2.9
NA
_____________________________________________________________________
NA = not analyzed
Table 12.2. Nutrient concentration summary statistics for Whiskey Creek, August 2005July 2006, as mean (standard deviation) / range, N/P ratio as mean / median.
62
_____________________________________________________________________
Nitrate
Ammonium
Phosphate Molar N/P ratio
(mg/L)
(mg/L)
(mg/L)
_____________________________________________________________________
WC-MB
0.024 (0.016)0.023 (0.022)0.012 (0.003)
8.1
0.003-0.057
0.001-0.074
0.007-0.019
WC-AB
0.033 (0.027)
0.007-0.097
WC-MLR
0.042 (0.028)0.035 (0.019)0.016 (0.007)
12.3
0.006-0.087
0.001-0.066
0.006-0.029
9.2
0.065 (0.023)0.143 (0.060)0.003 (0.003)
1175.8
0.040-0.107
0.074-0.287
0.001-0.009
182.9
WC-SB
WC-NB
NA
0.014 (0.007)
0.006-0.029
8.7
NA
0.174 (0.063)0.128 (0.063)0.007 (0.006)
218.9
0.087-0.294
0.063-0.260
0.002-0.017
112.7
_____________________________________________________________________
NA = not analyzed
63
Figure 12.1. Whiskey Creek. Watershed and sampling sites.
64
13.0 Results of Aerial Infrared Survey of City Watersheds
By
Brad A. Rosov and Michael A. Mallin
Center for Marine Science
University of North Carolina Wilmington
Introduction
In an effort to be innovative in locating potential sources of non point source pollution,
Wilmington City Stormwater Services contracted to conduct an aerial infrared survey of
Burnt Mill Creek, Bradley Creek, Hewletts Creek and Greenfield Lake. This effort,
termed “Illicit Discharge Detection and Elimination” was performed in partnership with
the University of North Carolina Wilmington’s Aquatic Ecology Laboratory within the
Center for Marine Science. On March 23, 2004 a low-altitude aerial infrared survey was
conducted over the fresh and brackish creeks in Wilmington in order to identify potential
locations of non-point discharge sites. Aerial infrared surveys conducted during cold
weather have become a common tool used to locate warmer water discharges into the
cooler ambient surface waters. These warmer water discharges could be groundwater
seeps, sanitary sewer connections or leaks, HVAC condensate lines, sump pump
discharge lines, etc. As shown in the photo, these discharges are at a higher water
temperature than surface water and are easily discernable through infrared imagery as
they appear much brighter than the cooler surface water (Photo 1). Geo-referenced
images from digital video depicting thermal anomalies were collected by Wilmington
Stormwater Services and provided to UNCW with recommendations for ground truthing.
Between August 2, 2006 and September 21, 2006, the UNCW Aquatic Ecology
Laboratory investigated the source and condition of water from 27 potential non-point
leaks. These sites were located within the Bradley Creek, Hewletts Creek, and Burnt
Mill Creek watersheds.
Methods
Using geo-referenced aerial images (see Photo 1), Google Earth software, and a
Garmin 76 handheld global positioning system, UNCW staff located the precise location
of individual potential leak sites. Sites were visited via jon boat or truck, depending on
specific location. If standing or flowing water was found, temperature and pH
measurements were acquired using a YSI 80 multi-parameter water quality instrument.
Water samples were collected from sites that appeared to be influenced by human
disturbance. Samples were placed on ice and delivered to a State-certified contract
laboratory for subsequent analysis for fecal coliform bacteria, biochemical oxygen
demand (BOD), surfactants, oil and grease, and nutrients (ammonium, TN, TP, total
Kjeldahl Nitrogen (TKN), and Nitrate).
65
Photo 1: Infrared image of a potential non-point leakage (depicted as a bright white)
Warmer
water
discharge
Results
UNCW staff visited 26 of the 27 sites in question. Site #57 was not able to be visited
due to limited access on private property. Of the 26 sites visited, 14 did not have
discernable water or flow and could not be sampled. Of the sites with apparent flow,
four sites originated through culverts, three through PVC or corrugated pipe, four were
situated along wooden docks, and one site originated from a raised mount septic
system or well. Samples were collected from 10 sites: #16, 22a, 24, 28a, 28b, 29, 67,
76a, 118, 120 (photo 2). Five sites (#16, 28a, 28b, 67, and 120) contained fecal
coliform bacteria counts above the 200 CFU/100ml standard (Table 2 in bold). Two of
the five sites analyzed for BOD (#16 and 67) contained high levels as well (Table 2 in
bold). Nutrient values, surfactant, and oil and grease values appeared to be within
normal ranges.
66
Conclusions
The finding of elevated fecal coliform bacteria counts at five sites and elevated BOD at
two sites has prompted the City and the University to further investigate these
anomalies. As such, Wilmington Stormwater Services, Public Utilities and the UNC
Wilmington Aquatic Ecology Laboratory have discussed the matter and have produced
a plan to conduct further sampling of the sites in question, as well as localized
wastewater pipe inspections and site visits to assess the reasons for the high values
and instigate corrective procedures if needed. These activities are to be carried out
during spring and summer of 2007.
Table 1. Sampling locations
Site
ID
Lat.
Long.
Bradley Creek
67
34.21639
-77.83389
Burnt Mill Creek
28a
34.24944
-77.92972
Large concrete sewer junction box sitting in wet marshy
area
Burnt Mill Creek
28b
34.24917
-77.92972
Standing or low flow marsh water running around/ beneath
sewage main
Burnt Mill Creek
29
34.24861
-77.92861
Sewage pipe running over small creek (with very little flow)
Burnt Mill Creek
24
34.23722
-77.92111
Flow present from storm drain running into Burnt Mill Creek
at Wallace Park
Burnt Mill Creek
22a
34.23583
-77.92
Flow present from ground water bubbling up into Burnt Mill
Creek (possible artesian well)
Watershed
Description
Neighborhood storm water runoff is channeled to the side of
the bridge (culvert runs from Bar Harbor Rd. to the edge of
Bradley Creek paralleling Oleander Dr.). A culvert gate was
found in the raised position.
Burnt Mill Creek
76a
34.23167
-77.85528
Flow present originating from a bulkhead in the back yard of
5314 Clear Run. Source is a black pipe and a white PVC
pipe and runs into Clear Run Branch (appears to by
drainage from yard)
Burnt Mill Creek
16
34.23139
-77.91306
Flow present from a storm water drain flowing into Burnt Mill
Creek adjacent to Elementary School
Hewletts
118
34.19306
-77.88778
Groundwater or storm water flowing from backyard into
creek
Hewletts
120
34.19
-77.89806
Corrugated black drainage pipe flowing from under golf
course to creek
Photo 2: Sampling site locations
67
Table 2: Results of water sample analysis (Bold values exceed standard)
Station
ID#
16
22a
24
28a
28b
67
76
29
118
120
BOD
(mg/l)
3.67
0.94
0.74
n/a
n/a
2.89
1.08
n/a
n/a
n/a
Fecal
Coliform
(cfus/100ml
)
1600
4
71
260
5400
350
30
155
19
420
Surfactants
(MBAS
mg/l)
0.038
<.012
0.016
n/a
n/a
0.114
0.029
n/a
n/a
n/a
Oil and
Grease
(mg/l)
n/a
n/a
2
n/a
n/a
2
n/a
n/a
n/a
n/a
Ammoniu
m (mg/l)
n/a
n/a
n/a
0.06
0.09
n/a
n/a
0.03
0.47
0.07
TP
(mg/l)
n/a
n/a
n/a
0.07
0.19
n/a
n/a
0.04
0.01
0.09
TKN
(mg/l)
n/a
n/a
n/a
1.1
1.4
n/a
n/a
1.3
0.9
1.4
Nitrate
(mg/l)
n/a
n/a
n/a
0.12
0.12
n/a
n/a
0.45
0.01
0.15
TN
(mg/l)
n/a
n/a
n/a
1.22
1.52
n/a
n/a
1.75
0.9
1.55
68
14.0 Fecal Indicator Bacteria in the Water and Sediments of Local Boat Ramps
Renee N. Harrington and Lawrence B. Cahoon
Department of Biology and Marine Biology
University of North Carolina Wilmington
910-962-3706, Cahoon@uncw.edu
Introduction
The need for water quality monitoring and management becomes increasingly important
as coastal populations increase. An increase in impervious cover, a direct result of urban
development, has been linked with increased nutrient inputs and fecal bacterial levels in
coastal environments (Mallin et al., 2000). Stormwater runoff has been cited as a large
contributor of these pollutants to receiving waters since bacteria deposited on or near
impervious surfaces accumulate and can be transported easily and rapidly into coastal
waterways with discharge and runoff (Davis et al., 1977). Pollutants entering surface
waters through urban stormwater include human and domestic animal wastes, which
contribute enteric microbes; fertilizers, pesticides, and herbicides from land development,
landscaping, and golf courses; other pollution from population growth; and bacteria from
decaying vegetation and soils, which may not be pathogenic (Mallin et al., 2000; Mallin et
al., 2001, Smith and Perdek, 2004).
A main focus of water quality management is on pathogens in the water that may cause
harm to humans. Increased levels of microbes have many impacts, primarily shellfishing
closures and human health risks (Mallin et al., 2000). Microbiological health risks
associated with exposure to bacteria-polluted coastal waters include infections of the skin,
ears, and eyes as well as respiratory disease (Dufour, 1986; Dadswell, 1993; Kwavnick
and Mortimer, 1999; USEPA, 2003; Smith and Perdek, 2004) from ingestion, inhalation,
and body contact (USEPA, 2003). Most of the pathogens responsible for disease and
infection are found in the feces of warm blooded animals and are most commonly
transported into coastal waters through sewage outfalls and runoff (USEPA, 2003).
Smith and Perdek (2004) stated that forty percent of all evaluated rivers and estuaries in
the United States have elevated concentrations of fecal coliform bacteria that fail to meet
the standards for ambient water quality. Standards are set at conservative levels above
which health risks may exist. These standards are 200 CFU/100ml for coliforms and 35
CFU/100ml for Enterococcus in saltwater and 33 CFU/100ml in fresh water (USEPA,
2003). Fecal indicator bacteria are used in water quality monitoring because they are
easy to test for and, although not pathogenic themselves, they tend to co-occur with
harmful fecal pathogens. High levels of fecal indicator bacteria have been correlated with
higher levels of illness in swimmers, thus indicator bacteria are used in water quality
monitoring programs to determine and restrict usage of recreational waters (Noble et al.,
2003).
Fecal coliform levels both in sediments and the water are known to be highly variable over
time; however, sediment bacterial levels have been referred to as a more stable indicator
than bacterial populations present in the overlying waters and a more reliable indicator of
trends in water quality (Van Donsel and Geldreich, 1971; Doyle et al., 1992). Bacteria in
the water column tend to adsorb to sediment particles and settle out (Weiss, 1951;
69
Schillinger, 1982; Marino and Gannon, 1991), where, in association with sediment, they
have a longer life span than in the water column due to higher nutrient levels (Chan et al.,
1979; An et al., 2002); protection from UV radiation, high salinity, and attack by
bacteriophages (Davies et al., 1995); and a large surface area for attachment and
absorption (La Liberte and Grimes, 1982; Doyle et al., 1992; Marsalek and Rochfort,
2004).
Sediment bound bacteria can be resuspended in a variety of ways, including human and
pet activity, dredging, storm events, and boat traffic (Pettibone et al., 1996). High
bacterial concentrations associated with waves and human activity, have been recorded
in coastal waters (Chan et al., 1979). Numerous other studies have reported sediment
resuspension to be responsible for degradation to water quality of the overlying waters
due to bacteria released into the water column (Grimes, 1975; Grimes, 1980; Doyle et al.,
1992, Pettibone et al., 1996, Mallin et al., 2006).
As monitoring for bacterial pollution becomes increasingly important, so is the necessity
for research regarding the controls on bacterial populations in the water column and at
the sediment surface. The coastal region of North Carolina is widely monitored for water
quality and swimmer safety. The primary water quality investigators are the Shellfish
Sanitation Section, which is responsible for the coastal water quality monitoring that
determines shellfishing and swimming beach closures, and the Division of Water Quality,
which has developed a series of basinwide management plans monitoring fish kills, algal
blooms, surface water discoloration and odors, groundwater contamination, and sewer
and stormwater runoff (North Carolina Coastal Federation, 2005).
Currently, one overlooked area in water quality monitoring is at boat launching ramps
where people come in contact with potentially polluted water and sediments. These
locations generally have expanses of pavement, residential development and associated
fecal sources, and are sloped into the water, providing an easy conduit for bacterial
pollution. Typically boat ramps are built in regions with slower water movement to allow
for easier launching and retrieving of boats. The calmer conditions, in relation to more
open waters such as rivers, bays, and beaches, also provide opportunity for bacteria to
bind to sediment and settle out. Disturbance to the sediment surface resulting from
activity at boat ramps could potentially release the sediment-bound bacteria back into the
water column at very high levels while people are in contact with the water. Therefore,
this is an unquantified but potentially serious health hazard.
Furthermore, it is necessary to identify the role resuspension has on bacterial levels in the
water because it has been determined that physical forces such as currents, wave action,
and sediment agitation can produce highly variable releases of sedimentary coliform
bacteria (Hillel, 1971). Conventional water sampling approaches that do not take into
account sediment bacteria, may not accurately quantify potential health hazards present.
Research becomes increasingly important with the knowledge that there is a direct
correlation between the concentration of fecal bacteria in the water and the occurrence of
infections from contact with this water (Coelho et al., 1999). The area of study, New
Hanover County in southeastern North Carolina, bordered by the Atlantic Ocean on the
eastern and the Cape Fear basin on the western extent, has many public and private boat
70
ramps used year round. Accordingly, water quality research examining sedimentassociated fecal bacteria at these currently unstudied locations is imperative.
This study was designed to investigate the quantity of fecal bacteria that are present in
the water and accumulate in the sediments at various publicly used boat ramp locations
in comparison to other publicly used locations. The ranges of bacterial levels present at
public use areas were used to determine the relative health risk present at boat ramps
compared to nearby locations where people routinely have contact with the water as well.
The sediment bacteria levels were used to determine the potential harm to overlying
waters in resuspension events and to determine if the disturbance at boat ramps is great
enough to release the sediment bound bacteria into the water column at levels high
enough to cause harm to humans, according to EPA water quality standards, when
exposed to the waters during and just after the disturbance.
Methods
Sediment samples were collected from 17 sites in New Hanover County (Figure 1).
Twelve sites were public use boat ramps and 5 served as comparison sites. Public
use areas, such as parks and other areas on the coast, where the public might routinely
come into contact with the water and sediments were used as comparison sites.
Samples were collected from boat ramp sites once per month from September 2004
through December 2005. Water samples were collected from the same sites once per
month from January 2005 through December 2005. Sediment and water samples were
collected from comparison sites for two to four months during September 2005 through
December 2005. All water and sediments samples were taken in a 1-m deep water
column.
At each site, two consecutive water samples were collected with sterilized 500 ml glass
bottles lowered approximately half way through the water column. The first was a clear
water sample taken without disturbing the underlying sediments. Immediately following
collection of the first water sample, sediment and water disturbance was achieved
through actual disturbance from boating activity at the ramp or human disturbance by
the sampler walking around in the water at the site. A second sample was then taken
immediately from the water column with the resuspended sediment load.
Sediment cores for bacterial analysis were collected by hand with sterilized, acid
washed PVC core tubes (2.3 cm diameter) following methods developed by Rowland
(2002). The tubes were pressed into the sediment surface to a depth of 2.5 cm, sealed
with a rubber stopper, and brought back to the surface where they were emptied into
sterilized, pre-weighed 50 ml polypropylene centrifuge tubes. All samples were
collected within one hour of low tide and taken in triplicate. Water column field
parameters (temperature and salinity) were collected using a hand-held YSI 85 Multiparameter water quality meter during each sampling.
71
Figure 1. Map of boat ramp (triangle) and non-boat ramp (diamond) sampling locations
in New Hanover County, N.C.
Water samples were analyzed in 500 ml duplicates or 100 ml triplicates according to
Standard Methods (APHA, 1998) for membrane filtration onto sterile membrane filters
72
(0.45µm pore size, 47 mm diameter). Dehydrated media were used to enumerate the
bacteria from the samples for the common bacterial indicators fecal coliform and fecal
Enterococcus. Coliform samples were incubated for 24 hr at 44.5°C on mFc agar
(APHA method 9222D) and Enterococcus samples for 48 hr at 41°C on mE agar
(APHA method 9230C.3.a) in Fisher Isotemp digital water baths.
Sediment samples were analyzed with the same technique following a suspension
procedure. Supernatant was pipeted from each sample in the lab. The sediment was
then mixed with 1L of sterile phosphate-buffered (0.25M KH2PO4, pH adjusted to 7.2
with 0.1N NaOH) rinse water in a sterile 1L beaker with a magnetic stir bar and gently
stirred for 2 min prior to membrane filtration of 50 ml duplicate or 10 ml triplicate subsamples. Counts obtained for sub-samples from each core were averaged and
2
expressed as the number of colony forming units per cm² (CFU/cm ) of cored sediment.
Data sets were examined for normality using the Shapiro-Wilk test and normalized by
log transformation (log(X+1). Correlation analyses were used to determine if significant
relationships existed between the two indicator bacteria in the sediment and between
bacterial concentrations in the sediment and water. One-way ANOVA was used to
determine if there was a significant increase in bacteria levels in the water column
following disturbance. Statistical analysis was performed using SAS Institute’s JMP
version 4.0. P values of <0.05 were defined as significant; values up to 0.07 were used
as accepted as significant owing to the highly variable nature of fecal indicator bacteria
concentrations in the environment. Bacterial standard of 200 CFU/100ml was used for
coliform and 35 CFU/100ml was used for Enterococcus due to the range of salinities.
Results
Sediment samples were collected from 12 boat ramp locations and 5 non-boat ramp
sites, yielding a total of 135 samples analyzed for fecal coliform and 133 samples
analyzed for fecal Enterococcus. Following normalization, correlation analysis was
used to examine the relationship between the indicator bacteria concentrations in
sediment. The two fecal bacteria indicators were found to be significantly correlated
with each other (r² = 0.46, F = 2.16, df = 1,157, p = 0.006) (Figure 2).
73
Enterococcus (log CFU/cm2)
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0.0
1.0
2.0
3.0
4.0
5.0
coliform (log CFU/cm2)
Figure 2. Relationship between sediment coliform and Enterococcus indicator bacteria.
The geometric mean of sediment bacteria concentrations were variable among sites,
with higher bacteria concentrations typically found at ”upstream” locations nearer
extensive watersheds, e.g., sites CH and CHC (on the northeast Cape Fear River in
Castle Hayne), or near drainage features, e.g., site BS (Bayshore Drive boat ramp
located at the headwaters of Page’s Creek), and the lowest concentrations nearest the
influence of oceanic waters, e.g., sites SS and WB (the Wrightsville Beach area)
(Figure 3). The high and low geometric means for coliform bacteria were at CHC
(1919 CFU/cm²) and SS (1 CFU/cm²), respectively. The high and low geometric means
for Enterococcus bacteria were at CHC (1476 CFU/cm²) and WB (1 CFU/cm²).
Concentrations of Enterococcus were more often above comparable standards than
coliform concentrations measured at the same locations.
There was a significant correlation between bacteria in the sediment and associated
water for both coliforms (r² = 0.999, F = 2490 df = 1,109, p = <0.0001) and
Enterococcus (r² = 0.975, F = 26.9, df = 1,107, p = <0.0001). These data indicate the
sediment surface could be an important source of bacterial contaminants via
resuspension of the sediment, particularly Enterococcus, where the resuspensioninduced increase of bacteria in the water would lead to a greater percent of samples
that exceed comparable water quality standards (Figure 4). Enterococcus displayed a
greater increase of bacteria in the water column than coliforms following disturbance of
the water column and associated sediments. One-way ANOVA was used to determine
if there was a significant increase in bacteria levels in the water column following
disturbance. Both coliforms and Enterococcus exhibited significant post-disturbance
increases (F = 1.51, df = 1,133, p = 0.0651; F = 74.8, df = 1,133, p = <0.0001,
respectively).
74
A
Geometric mean of sediment
coliform (CFU/cm²)
10000
1000
100
10
1
AN ANC AR
BS
CH CHC CSP FF
JM
ML MM PP
RP
RR
SS
TE WB
ML MM PP
RP
RR
SS
TE WB
Site
B
Geometric mean of sediment
Enterococcus (CFU/cm²)
10000
1000
100
10
1
AN ANC AR
BS
CH CHC CSP FF
JM
Site
Figure 3. Geometric mean of coliform (A) and Enterococcus (B) indicator bacteria
concentrations at each sampling location. The 5 non-boat ramp sites (ANC, AR,
CHC, SS, WB) are plotted with the boat ramp locations (all other sites). Limits set
for swimmer safety for the indicator bacteria are noted with a bold horizontal line,
200 CFU/100ml for coliforms and 35 CFU/100ml for Enterococcus.
75
Percent of Samples that Exceeded EPA Water Quality Standards
60
51
Percent
50
38
40
Pre-disturbance
30
20
10
9
Post-disturbance
13
0
coliform
Enterococcus
Indicator Bacteria
Figure 4. Percent of sediment samples that exceeded EPA water quality standards for
coliforms and Enterococcus measured pre- and post-disturbance based on hypothetical
distribution in 1-m of water.
Table 1 presents the geometric mean for coliform and Enterococcus concentrations
measured in the sediment at each site. The hypothetical noncompliance was
determined from the percent of sediment sample values measured for each site that
exceeded EPA swimmer safety limits with the assumption that if the bacteria found in 1
2
cm of sediment surface are suspended into a 1-m deep water column (= 100ml of
water) the resulting unit is CFU/100ml, which is the standard unit used for water quality
monitoring and standards. This technique relies on the assumptions that resuspension
is 100 percent effective and that bacteria are evenly distributed in the water column.
Average indicator sediment bacteria values exceeded standards at some sites and
exceeded more frequently with Enterococcus. All non-ramp sites, except CHC, had
zero percent exceedence for coliforms, where as boat ramp sites had percent
exceedences that were variable ranging from 0 percent to 70 percent. All sites had
higher percent exceedences for Enterococcus than coliforms and most boat ramp
locations had a higher percent exceedence than non-ramp locations. The geometric
mean presented for water samples pre- and post-disturbance showed that in general,
water column bacteria increased following disturbance.
All sites are further compared in Table 2 with summary data (count, mean, standard
deviation, median, and geometric mean) calculated for both coliform and Enterococcus
at boat ramp and non-ramp sites. Non-ramp sites had higher mean and geometric
mean than at boat-ramp locations due to a lower samples size and high values
measured at CHC which skewed the calculations. Removing data for CHC from
calculations substantially lowered the values for both coliforms and Enterococcus
indicating that the other non-ramp sites had values that were much lower than CHC and
all ramp sites together.
76
Table 1. Percent of samples that exceeded bacterial standards, geometric
mean of sediment samples, water column pre-disturbance, and water column
post-disturbance of (A) coliforms and (B) Enterococcus for each site. Nonramp sites are distinguished in bold.
A
coliforms
Site
AN
ANC
AR
BS
CH
CHC
CSP
FF
JM
ML
MM
PP
RP
RR
SS
TE
WB
Percen
t
Exceed
8
0
0
70
25
100
14
0
9
18
0
7
36
8
0
21
0
Mean Sediment
(CFU/100ml)
14
4
9
264
86
1919
11
25
8
20
2
6
96
22
1
31
9
Mean water column preDisturbance (CFU/100ml)
14
7
13
259
32
26
20
40
20
13
11
17
60
83
8
38
8
Mean water column postDisturbance (CFU/100ml)
25
16
59
171
51
41
32
40
32
35
21
24
74
118
34
56
28
B
Enterococcus
Site
AN
ANC
AR
BS
CH
CHC
CSP
FF
JM
ML
MM
PP
RP
RR
SS
TE
WB
Percen
t
Exceed
85
10
50
100
38
100
57
79
73
27
11
7
50
54
50
50
50
Mean Sediment
(CFU/100ml)
145
96
12
329
14
1476
46
85
90
13
6
7
44
25
12
31
1
Mean water column preDisturbance (CFU/100ml)
26
24
4
117
13
190
7
19
23
13
13
4
31
45
4
17
2
Mean water column postDisturbance (CFU/100ml)
55
4
5
128
27
237
11
42
27
17
17
12
46
70
4
23
6
77
Table 2. Summary data (number of samples (n), mean, standard deviation, median,
and geometric mean) for all non-ramp sites compared to all boat ramp locations.
n
coliforms
Non-ramp sites
Boat ramps
Non-ramp w/o CHC
Enterococcus
Non-ramp sites
Boat ramps
Non-ramp w/o CHC
13
122
9
12
121
9
Mean +/- Standard Deviation
(CFU/100ml)
Median
(CFU/100ml)
Geometric Mean
(CFU/100ml)
1307 +/- 3049
626 +/- 2828
25 +/- 38
76
23
0
28
22
4
1912 +/- 5808
308 +/- 1091
68 +/- 71
76
53
76
45
37
14
Discussion
The distinct correlation between the two indicator bacteria measured, fecal coliform and
Enterococcus, supports the functionality of using either or both indicator bacteria types
to test for potential pathogens and the risks they pose in a variety of aquatic locations.
Enterococcus concentrations exceeded human health-based standards more frequently
than the coliform concentrations measured in the same sediment, suggesting
Enterococcus is a more conservative measure. This study revealed fecal indicator
bacteria concentrations in the sediment at some of the sites that were consistently great
enough to impair the overlying waters post-disturbance, which is consistent with other
studies that have recognized sediment as a reservoir for bacteria (Van Donsel and
Geldreich, 1971; LaLiberte and Grimes, 1982; Doyle et al, 1992; Davies et al, 1995). In
New Hanover County, bacterial concentrations were usually greater at upstream
locations than at sites nearer the ocean, indicating these areas are particularly at risk in
terms of water quality and threats to public health. High bacteria concentrations in
sediments at several sites, notably BS and CHC, suggested proximal sources of fecal
contamination, perhaps from human sources, pets, or wildlife in the area.
The results suggest that water quality at boat ramp locations is frequently at an
undesirable level and that boating activity can cause immediate water quality
degradation in an area when the bacteria maintained in the sediments are disturbed.
The re-suspension data collected during this study indicates that background
Enterococcus bacteria levels at many of the sites can create non-compliant waters
almost instantaneously with disturbance. Bacterial densities in the water column
following disturbance were commonly much greater than those in samples collected
when sediments were not disturbed. In addition, the relatively higher levels of
Enterococcus post-disturbance suggest these bacteria are much more easily
resuspended than coliforms. Relative harm, calculated from bacteria concentration in
the sediment, indicates any re-suspension event would degrade water quality in the
immediate area and pose a threat to waders and swimmers. The distinct correlation
between indicator bacteria measured in the sediment and corresponding waters further
emphasizes the considerable effect resuspension of sediments can have on water
78
quality and the significance of utilizing sediment bacteria measurements in water quality
monitoring.
The results of this study have potentially important implications for other recreational
areas in coastal North Carolina. Primarily, these results suggest that sediment
sampling is important for recreational waters where sediments can act as a reservoir for
pathogenic enteric bacteria. Fecal bacteria measured in the water column are
associated with recent contamination, whereas sediments serve as a reservoir and may
serve as a better representation of the contaminant history in the area. These results
will serve as a foundation for more in-depth sampling and health risk assessments of
recreational coastal waters. Secondly, the results emphasize the importance of limiting
storm water, nutrient inputs, and other sources of contamination in highly developed
coastal areas. Currently there are initiatives to decrease nutrient and bacterial inputs
into coastal waters of North Carolina. Additional consideration should be given to future
sampling needs and regulations for boat ramp locations in order to protect human
health.
References
An, Y.-J., Kampbell, D.H., and Breidenbach, G.P., 2002. Escherichia coli and total
coliforms in water and sediments at lake marinas. Environmental Pollution. 120: 771778.
APHA (American Public Health Association), 1998. Standard methods for the
th
examination of water and wastewater. 19 edition. American Public Health
Association, Washington, D.C., USA.
Chan, K.-Y., Wong, S.H., and Mak, C.Y., 1979. Effects of bottom sediments on the
survival of Enterobacter aerogenes in seawater. Marine Pollution Bulletin. 10: 205210.
Coelho, M.P., Marques, M.E., and Roseiro, J.C., 1999. Dynamics of microbiological
contamination at a marine recreational site. Marine Pollution Bulletin. 38(12): 12421246.
Dadswell, J.V., 1993. Microbiological quality of coastal waters and its health effects.
International Journal of Environmental Health Research. 3:32-46.
Davies C.M., Long J.A.H., Donald M., and Ashbolt, N.J., 1995. Survival of fecal
microorganisms in marine and freshwater sediments. Applied and Environmental
Microbiology. May: 1888-1896.
Davis, E.M., Casserly, D.M., and Moore, J.D., 1977. Bacterial relationships in
stormwaters. Water Resources Bulletin. 15:895-905.
Doyle J.D., Tunnicliff B., Kramer R., Kuehl R., Brickler, S.K., 1992. Instability of fecal
coliform populations in waters and bottom sediments at recreational beaches in
Arizona. Water Resources. 26(7): 979-988.
79
Dufour, A.P., 1986. Diseases caused by water contact. In Craun, G.F., ed. Waterborne
diseases in the United States. Boca Raton: CRC Press.
Grimes, D.J., 1975. Release of sediment-bound fecal coliforms by dredging. Applied
Microbiology. 29: 109-111.
Grimes D.J., 1980. Bacteriological water quality effects of hydraulically dredging
contaminated Upper Mississippi River sediment. Applied Environmental
microbiology. 36: 782-789.
Hillel, D. 1971. Soil and water physical principles and processes. Third Edition,
Academic Press, New York. 288p.
Kwavnick, B. and Mortimer, J, 1999. Lake Erie lakewide management plan (LaMP)
technical report series. Recreational water quality impairments (bacterial levels and
beach postings). Lake Erie LaMP technical report no. 12.
La Liberte P. and Grimes, D.J., 1982. Survival of Escherichia coli in lake bottom
sediment. Applied and Environmental Microbiology. 43:623-628.
Mallin, M.A, Williams, K.E., Esham, E.C, and Lowe, R.P., 2000. Effects of human
development on bacteriological water quality in coastal watersheds. Ecological
Applications, 10(4):1047-1056.
Mallin, M.A., Ensign, S.H., McIver, M.R., Shank, G.C., and Fowler, P.K., 2001.
Demographic, landscape, and meteorological factors controlling the microbial
pollution of coastal waters. Hydrobiologia, 460: 185-193.
Mallin, M.A., L.B. Cahoon, B.R. Toothman, D.C. Parsons, M.R. McIver, M.L. Ortwine
and R.N. Harrington. 2006. Impacts of a raw sewage spill on water and sediment
quality in an urbanized estuary. Marine Pollution Bulletin, 54: 81-88.
Marino, R.P. and Gannon, J.J. (1991). Survival of fecal coliforms and fecal streptococci
in storm drain sediment. Water Research, 25: 1089-1098.
Marsalek, J. and Rochfort, Q., 2004. Urban wet-weather flows: sources of fecal
contamination impacting on recreational waters and threatening drinking-water
sources. Journal of Toxicology and Environmental Health, part A. 67: 1765-1777.
Noble R.T., Moore D.F., Leecaster M.K., McGee C.D., and Weisberg, S.B., 2003.
Comparison of total coliform, fecal coliform, and enterococcus bacterial indicator
response for ocean recreational water quality testing. Water Research, 37: 16371643.
North Carolina Coastal Federation, Coastal Contact Information. Date accessed
4/10/2005. <http://www.nccoast.org/contactinfo.htm>
80
Pettibone, G.W., Irvine, K.N., and Monahan, K.M., 1996. Impact of a ship passage on
bacteria levels and suspended sediment characteristics in the Buffalo River, New
York. Water Resources. 30:2517-2521.
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, UNCW Wilmington, Wilmington, N.C.
Schillinger, J.E., 1982. Bacterial adsorption to suspended particles in urban stormwater.
Dissertation University of Michigan.
Smith Jr, J.E. and Perdek, J.M., 2004. Assessment and management of watershed
microbial contaminants. Critical Reviews in Environmental Science and Technology,
34: 109-134.
USEPA, 2003. Bacterial water quality standards for recreational waters (freshwater and
marine waters) status report. EPA-823-R-03-008. U.S. Environmental Protection
Agency, Office of water (4305T). Washington, DC. 20460.
Van Donsel D.J. and Geldreich E.E., 1971. Relationships of Salmonella to fecal
coliforms in bottom sediments. Water Resources. 5: 1079-1087.
Weiss, C.M., 1951. Adsorption of E. coli on river and estuarine silts. Sewage Industrial
Wastes. 23: 227-237.
81
15.0 Evaluation of Oyster Characteristics in
Pages, Howe, and Hewletts Creeks
Troy Alphin and Martin Posey
Center for Marine Science
University of North Carolina Wilmington
Introduction
The tidal creek systems in New Hanover County, North Carolina, represent a very
unique resource to this area. Each of the tidal creeks in New Hanover County
represents a “mini-estuary” ranging in length from 2-5 kilometers, headwaters to mouth,
with a unique history of land use and development. As the amount of development
increases, the need and demand for the wise management of these critical areas
increases, including obtaining information on key ecological and ecosystem
characteristics that may help identify status and trends. Initial studies of the bivalve
communities in Hewletts, Bradley, Howe and Pages Creeks were conducted in 19931995. At that time the distribution of bivalves in the creeks was reduced relative to
anecdotal accounts by long term residents of the creeks (Mallin et al. 1995). The
decline was blamed on development, but with few indications of a reduction in planned
projects. Water quality within the creeks has generally declined in the decade since the
original study and shellfish closures have reduced the acreage of shellfish bottom in all
the creeks. These findings indicate a continued erosion of water quality and a loss of
ecological function. Concerned citizen groups, non-governmental organizations, and
county representatives have expressed concern for the impacts to the creek systems,
but few actions have been taken to reduce the current impacts or slow the rate of inputs
into the creeks. In 2004 and 2005 the southern Regional Oyster Steering Committee
for the North Carolina Coastal Federation (NCCF) made tidal creek systems of New
Hanover County one of their primary focus areas for study and restoration efforts. The
NCCF along with the UNCW’s Benthic Ecology Laboratory (BEL) and the North
Carolina Division of Marine Fisheries (DMF) have planted and monitored oyster reef
restoration sites in Hewletts Creek and areas adjacent to the intracoastal waterway
(ICW). But these efforts focus on best practices for the successful restoration and
establishment of oyster reefs and on determining reasonable metrics to judge
restoration success rather than assessment of the health of remaining beds.
As stated in our previous report, the southern fishery region continues to suffer from
three main problems related to shellfish; 1) Oyster stocks within the southern regions
(especially New Hanover and Onslow Counties) are declining, 2) The decline is
coincident with the closure of shellfish grounds due to failure of these areas to meet
shellfish sanitation standards, 3) Available acreage for shellfish harvest has declined
over the last decade, with few indications that it will recover without regulatory help.
Closure of shellfish bottom to harvest seems to closely track human population growth
and associated development within the watershed.
82
Previous requests to the North Carolina Marine Fishery Commission have focused on
establishing more managed shellfish bottom (area DMF would “seed” with juvenile
oysters to be harvested in subsequent years). But this action only affects the local
harvesters and does not directly address the root problem of ecosystem changes
associated with declining shellfish health and abundance or poor development
practices. Shellfish perform several critical ecosystem functions including improving
water quality (removal of particles from the overlying water), habitat provision (critical
habitat for juveniles of certain fishery species), and reduced erosion to certain shoreline
areas. These functions are often related to oyster density, oyster size, reef
characteristic (e.g. how well-developed a reef is) and the health of oysters residing in
the areas (e.g. actual oyster size relative to the size of its shell, water content of an
oyster, disease incidence, etc.). Information is needed comparing the density and
condition of oysters among tidal creeks, as well as an assessment of overall reef
characteristics, both as a baseline for comparison to other systems and previous
studies and to allow better determination of development effects. One major problem
facing coastal ecosystems is the number of active developments within a given
watershed and the size of those developments relative to the size of the watershed and
distance from the waterway, too many active land-disturbing projects at one time seem
to impact the resources to a far greater extent than the same level of development
spread out over a longer time period. But we need additional information on the direct
relationship between oyster condition and watershed inputs and ecosystem function in
order to make any recommendations on acceptable levels of inputs.
During the 2005-2006 sampling year, the UNCW Benthic Ecology Laboratory
conducted studies of oyster reef health in 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 beds and a PNA (primary nursery
area), indicating that this area is key in 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 had been considered the most impacted of
the tidal creeks in New Hanover County due to sedimentation, nutrient runoff and
frequent sewage spills leading to shellfish closures throughout most of the creek and
portions of the ICW. Our study focused on evaluating the actual condition of the oyster
stocks in each of these creek systems. This study compares the oyster populations
among the three creeks focusing primarily on size demography, condition index, growth,
and disease intensity.
Methods
Sampling was conducted in summer 2006 and winter 2006 to coincide with sampling
conducted in 2005. Oyster populations were sampled in Hewletts Creek, Howe Creek,
and Pages Creek. Live oyster density, percent shell cover, size demography, condition,
shell height, and reef 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.
83
Quadrate sampling
Each reef was sampled by random placement of ten 50cm x 50cm square quadrats.
Percent shell cover was calculated within the 50cm X 50cm quadrats using a 16 point
grid system. Percent cover was determined by calculating the number of points that
were over live oyster or shell versus non-shell tideflat area; for the purpose of this report
both shell hash and live oysters were combined to determine percent cover. In order to
determine oyster density, the number of live oysters within each quadrate was counted.
Size demography refers to the overall distribution of sizes for live oysters present and
was calculated by measuring a random selection of twenty live oysters per quadrat. 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
Rugosity is a measure of how well a reef is developed (well-developed and growing
reefs are generally associated with higher rugosity). Rugosity was measured by random
sampling at five points per reef. A 100cm chain was draped across the reef in a
straight line. The 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 Condition
Oyster condition was calculated using 30 oysters >75mm shell height. This size class
represents oysters that are mature and of legal harvest size. These oysters have been
resident within the creek the longest and so may reflect the average conditions within
that system. Condition index, a ratio of soft tissue dry weight to internal shell volume,
was calculated for each oyster (Lawerence and Scott 1982, Abbe and Albright 2003).
This is a measure of soft tissue growth and is considered to be an indicator of oyster
health (Austin et al. 1993). In order to determine the internal shell volume, a water
displacement method was used. The volume of water displaced for the whole oyster
and when the shucked oyster (i.e. empty shell) is placed in a graduated cylinder to
determine the internal shell volume. Dry tissue weight was obtained after oyster tissues
have been dried for 24 hours at 70°C.)
Results
As in 2005 the oyster populations among the three creeks looked very similar. Size
distribution among the three creeks showed slight but predictable differences between
summer and winter seasons (Figures 1-3). There are proportionally fewer oysters in
the small size classes in the winter samples than in the summer samples mainly due to
recruitment of oyster spat throughout the summer.
Live oyster density showed a similar pattern between 2005 and 2006 for summer
sampling with significantly greater density of oysters overall in Howe Creek compared to
either Hewletts or Pages and no difference between Hewletts and Pages Creeks
(Figure 4). The samples collected for winter 2006 (Dec. ’05 to Jan. ’06) showed no
difference among the three creeks.
84
Comparison of mean size (shell height) among the creeks shows an interesting pattern
with oysters in Pages Creek significantly larger than either Hewletts or Howe in both
summer 2005 and 2006. Winter 2006 shows all three creeks to be different from one
another with Howe> Pages> Hewletts (Figure 5).
Reef rugosity was sampled each season along with other parameters however this
characteristic of oyster reefs changes much more slowly than parameters such as live
oyster density. We have combined the data for three sampling season to provide a
better estimate of the vertical complexity among the three creeks (Figure 6). Vertical
complexity did not differ significantly among the three creeks but it is important to point
out that Howe Creek vertical complexity seems to be declining. If this tend continues
these differences will be significant with the addition of another sampling year.
Percent shell cover did show a significant difference among creeks with oyster reefs in
Pages Creek having on average ~10% greater coverage than oyster reefs in Hewletts
Creek and ~20% greater coverage than oyster reefs in Howe Creek (Figure 7).
Because of complaints by local oystermen regarding regular die offs of oyster in some
locations, sets of oysters were deployed in each creek to monitor mortality from July
through November 2006 (a period of high stress following spawning in the spring and
early summer). The results of this study provide a reason for concern over recent
changes in Howe Creek. There were significant differences in the mortality rate among
the three creeks (Figure 8). Greater than 85% of the oysters marked and monitored in
Howe Creek died within the first month. A subsequent deployment did not survive any
better. Pages Creek also showed a relatively high rate (22-37%) of mortality in the
August and September sampling. In contrast, Hewletts Creek showed a consistent but
low mortality rate. Oyster handling was identical for all three creeks. Field observations
indicate a relatively high sedimentation rate in Howe Creek during this time period
(Table 1), with several of the reefs receiving high amounts of silt and sand. This is likely
a contributing factor to the mortality in Howe Creek but does not explain the mortality in
Pages Creek. Also, the high suspended sediment load occurring in August in Hewletts
Creek did not cause unusual mortality.
Analysis of condition index among the three creeks showed no significant difference
among the creeks for the summer 2005 and winter 2006 periods, but showed a strong
difference among the three creeks in summer 2006 (Figure 9). Pages Creek had the
lowest condition followed by Howe Creek and oysters in Hewletts Creek had
significantly greater condition measures during that period.
Conclusions
A priori we had expected Pages Creek to show greater measures of oyster health
compared to either Hewletts or Howe Creeks. Interestingly Howe Creek showed the
greatest oyster density in summer 2006 as it did in summer 2005, mostly likely due to
high larval set in the early summer. Apparent differences in oyster size were seen
among the creeks with larger mean sizes in Pages during summers and in Howe during
Winter. This difference may be due to differential mortality among small size classes in
the creeks or differential settlement of new recruits in Hewletts and Pages Creeks
85
(Figures1-3). The condition index tells us a lot about the health of the oysters, with
larger oysters found in Pages and Howe Creeks but low conditions in these same
areas. This indicates the oysters may be increasing their shell height but not increasing
the amount of soft tissue within the shells. Oysters growing in areas with high
suspended solids or areas where sedimentation may cover the oysters might be
expected to increase shell height to prevent burial. Based on anecdotal observations of
sedimentation among the three creeks, it seems that Howe Creek oysters in the target
reefs may be experiencing some degree of burial however an ongoing study of TSS
initiated in August 2006 did not show a marked difference in TSS levels among the
three creeks (Table 1). Currently we have no observations of high sedimentation to
explain the results for Pages Creek. Observations of high mortality among oyster
placed in Howe Creek may be due to an interaction of parameters not measured as
part of this study (i.e. predators, chemical factors, etc.), but it seems unlikely that
sedimentation alone can explain the mortality.
While a number of areas within the tidal creeks are already closed to shellfishing due to
bacterial contamination, this study indicates we are seeing impacts to the oysters
themselves. Previous assumptions were that areas closed to shellfishing due to fecal
coliform counts would act as shellfish sanctuaries and source populations for the
surrounding estuary. These data suggest that the oysters in these systems are
stressed. Moreover, impacts on size distributions and oyster condition may also impact
their ability to serve critical ecosystem functions such as filtering and habitat provision.
These areas are vital to provide larval to areas outside the creeks. Steps must be
taken quickly to stop the apparent decline of oyster health within these creeks and to
restore and protect the remaining stocks.
Literature Cited
Abbe, G.R. and B.W. Albright. 2003. An improvement to the determination of meat
condition index for the eastern oyster Crassostrea virginica. J. Shellfish Res. 22
(3);747-752.
Austin, H., D.S. Haven, and M.S. Moustafa. 1993. The relationship between trends in
a condition index of the American Oyster, Crassostrea virginica and environmental
parameters in three Virginia estuaries. Estuaries. 16(2);362-374.
Lawerence, D.R. and G.I. Scott. 1982. The determination and use of condition index
of oysters. Estuaries. 5(1):23-27.
Mallin, M., L. Cahoon, J. Manock, J. Merritt, M. Posey, T. Alphin, and R. Sizemore. 1995.
Water Quality in New Hanover County Tidal Creeks, 1994-1995. Annual report
submitted to New Hanover County and the Northeast New Hanover Conservancy.
86
90
80
70
Frequency
60
50
40
30
20
10
0
5 10 10 15 1520
2025
2530
3035
3540
4045
4550
5055
5560
6065
6570
7075
7580
8085
8590
9095
95- 100- 105+
100 105
Size Class
Figure 1. Size distribution of oysters from all three creeks Summer 2005.
Hewletts
Howe
Pages
90
80
70
Frequency
60
50
40
30
20
10
0
5 10 10 15 1520
2025
2530
3035
3540
4045
4550
5055
5560
6065
6570
7075
7580
8085
8590
9095
95- 100- 105+
100 105
Size Class (mm)
Figure 2. Size distribution of oysters from all three creeks Winter 2006
(Dec '05-January '06).
Hewletts
Howe
Pages
87
90
80
70
Frequency
60
50
40
30
20
10
0
5 10 10 15 1520
2025
2530
3035
3540
4045
4550
5055
5560
6065
6570
7075
7580
8085
8590
9095
95- 100- 105+
100 105
Size Class (mm)
Figure 3. Size distribution of oysters from all three creeks Summer 2006.
Hewletts
Howe
Pages
90
a
80
A
Oyster Density(0.25m2)
70
60
B
b
B
50
b
40
30
20
10
0
Summer 2005
Winter 2006
Summer 2006
Figure 4. Mean oyster density for all seasons sampled.
Hewletts
Howe
Pages
88
66
a
Height of Individual oyster (mm)
64
b
62
A
A
60
AB
B
58
c
B
56
B
54
52
50
48
Summer 2005
Winter 2006
Summer 2006
Figure 5. Mean size of oysters by season.
Hewletts
Howe
Pages
0.7
0.68
Rugosity
0.66
0.64
0.62
0.6
0.58
0.56
Figure 6. Mean rugosity by creek all seasons combined.
Hewletts
Howe
Pages
89
1
A
B
0.9
C
0.8
Percent cover
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Figure 7. Mean calculated percent shell cover of reefs per creek for
all season combined.
Hewletts
Howe
Pages
100
90
86
Mortality (% per Month)
80
70
60
50
40
37
30
22.2
20
10
8.2
7.6
6
4.7
2.1
0
0
Aug
Sept
Oct
Nov
Figure 8. Mortality of deployed oysters July '06-Nov. '06.
Hewletts
Howe
Pages
90
25
A
Condition Index
20
15
B
10
C
5
0
Summer 2005
Winter 2006
Summer 2006
Figure 9. Mean condition index of 75+ mm oysters by creek and season.
Hewletts
Howe
Pages
Table 1. Water column total suspended solids and percent organic content collected
from Hewletts Creek, Howe Creek, and Pages Creek starting in August 2006. Standard
error values are in parenthesis.
Parameters
Total Suspended Solids (mg/L)
Creeks
Hewletts
Howe
Pages
Percent organics
August
September
October
November
August
September
October
November
53.6(5.22)
38(7.92)
25.3(3.80)
22.3(1.88)
31(2.57)
19.1(0.86)
27.1(2.26)
30.4(3.96)
20.1(2.69)
63.1(22.2)
22.4(1.76)
16.8(1.52)
20.3(2.90)
23.7(1.42)
24.9(0.67)
29.3(1.25)
24.3(0.76)
23.3(0.49)
25.8(3.09)
19.5(0.94)
23.6(1.39)
29(2.56)
23.4(1.20)
24(1.10)
91
92
16.0 Report References Cited
APHA. 1995. Standard Methods for the Examination of Water and Wastewater, 19th
ed. American Public Health Association, Washington, D.C.
Hecky, R.E. and P. Kilham. 1988. Nutrient limitation of phytoplankton in freshwater and
marine environments: A review of recent evidence on the effects of enrichment.
Limnology and Oceanography 33:796-822.
Long, E.R., D.D. McDonald, S.L. Smith and F.D. Calder. 1995. Incidence of adverse
biological effects within ranges of chemical concentrations in marine and estuarine
sediments. Environmental Management 19:81-97.
Mallin, M.A., L.B. Cahoon, J.J. Manock, J.F. Merritt, M.H. Posey, R.K. Sizemore, W.D.
Webster and T.D. Alphin. 1998a. A Four-Year Environmental Analysis of New
Hanover County Tidal Creeks, 1993-1997. CMSR Report No. 98-01, Center for
Marine Science Research, University of North Carolina at Wilmington, Wilmington,
N.C.
Mallin, M.A., L.B. Cahoon, J.J. Manock, J.F. Merritt, M.H. Posey, T.D. Alphin, D.C.
Parsons and T.L. Wheeler. 1998b. Environmental Quality of Wilmington and New
Hanover County Watersheds, 1997-1998. CMSR Report 98-03. Center for Marine
Science Research, University of North Carolina at Wilmington, Wilmington, N.C.
Mallin, M.A., S.H. Ensign, D.C. Parsons and J.F. Merritt. 1999. Environmental Quality of
Wilmington and New Hanover County Watersheds, 1998-1999. CMSR Report No.
99-02. Center for Marine Science Research, University of North Carolina at
Wilmington, Wilmington, N.C.
Mallin, M.A. and T.L. Wheeler. 2000. Nutrient and fecal coliform discharge from coastal
North Carolina golf courses. Journal of Environmental Quality 29:979-986.
Mallin, M.A., S.H. Ensign, D.C. Parsons, V.L. Johnson and J.F. Merritt. 2000a.
Environmental Quality of Wilmington and New Hanover County Watersheds, 19992000. CMSR Report No. 00-02. Center for Marine Science, University of North
Carolina at Wilmington, Wilmington, N.C.
Mallin, M.A., K.E. Williams, E.C. Esham and R.P. Lowe. 2000b. Effect of human
development on bacteriological water quality in coastal watersheds. Ecological
Applications 10:1047-1056.
Mallin, M.A., L.B. Cahoon, R.P. Lowe, J.F. Merritt, R.K. Sizemore and K.E. Williams.
2000c. Restoration of shellfishing waters in a tidal creek following limited dredging.
Journal of Coastal Research 16:40-47.
Mallin, M.A., L.B. Cahoon, M.H. Posey, L.A. Leonard, D.C. Parsons, V.L. Johnson, E.J.
Wambach, T.D. Alphin, K.A. Nelson and J.F. Merritt. 2002a. Environmental Quality
of Wilmington and New Hanover County Watersheds, 2000-2001. CMS Report 02-
93
01, Center for Marine Science, University of North Carolina at Wilmington,
Wilmington, N.C.
Mallin, M.A., S.H. Ensign, T.L. Wheeler and D.B. Mayes. 2002b. Pollutant removal
efficacy of three wet detention ponds. Journal of Environmental Quality 31:654-660.
Mallin, M.A., L.B. Cahoon, M.H. Posey, D.C. Parsons, V.L. Johnson, T.D. Alphin and
J.F. Merritt. 2003. Environmental Quality of Wilmington and New Hanover County
Watersheds, 2001-2002. CMS Report 03-01, Center for Marine Science, University
of North Carolina at Wilmington, Wilmington, N.C.
Mallin, M.A., 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, 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., L.B. Cahoon, M.H. Posey, V.L. Johnson, D.C. Parsons, T.D. Alphin, B.R.
Toothman, M.L. Ortwine and J.F. Merritt. 2006. Environmental Quality of Wilmington
and New Hanover County Watersheds, 2004-2005. CMS Report 06-01, Center for
Marine Science, University of North Carolina at Wilmington, Wilmington, N.C.
NCDEHNR. 1996. Water Quality Progress in North Carolina, 1994-1995 305(b) Report.
Report No. 96-03. North Carolina Department of Environment, Health, and Natural
Resources, Division of Water Quality. Raleigh, N.C.
Parsons, T.R., Y. Maita and C.M. Lalli. 1984. A Manual of Chemical and Biological
Methods for Seawater Analysis. Pergamon Press, Oxford. 173 pp.
Schlotzhauer, S.D. and R.C. Littell. 1987. SAS system for elementary statistical
analysis. SAS Institute, Inc., SAS Campus Dr., Cary, N.C.
U.S. EPA. 1997. Methods for the Determination of Chemical Substances in Marine and
Estuarine Environmental Matrices, 2nd Ed. EPA/600/R-97/072. National Exposure
Research Laboratory, Office of Research and Development, U.S. Environmental
Protection Agency, Cincinnati, Ohio.
US EPA. 2004. National Coastal Condition Report II. EPA-620/R-03/002. United States
Environmental Protection Agency, Office of Research and Development, Office of
Water, Washington, D.C.
Welschmeyer, N.A. 1994. Fluorometric analysis of chlorophyll a in the presence of
chlorophyll b and phaeopigments. Limnology and Oceanography 39:1985-1993.
94
17.0 Acknowledgments
Funding for this research was provided by New Hanover County, the City of
Wilmington, the US EPA 319 Program through NC DWQ and North Carolina State
University, and the University of North Carolina at Wilmington. For project facilitation
and helpful information we thank Ed Beck, Delores Bradshaw, Pam Ellis, Matt Hayes,
David Mayes, Chris O’Keefe, Jim Quinn, Ken Vogt and Dave Weaver. For field and
laboratory assistance we thank Matt McIver, Rena Spivey, Kimberly Duernberger and
Asher Williams.
95
18.0 Appendix A. North Carolina Water Quality standards for selected parameters
(NCDEHNR 1996).
_____________________________________________________________________
Parameter
Standard
_____________________________________________________________________
Dissolved oxygen
5.0 ppm (mg/L)
Turbidity
25 NTU (tidal saltwater)
50 NTU (freshwater)
Fecal coliform counts
14 CFU/100 mL (shellfishing waters), and more than 10% of
the samples cannot exceed 43 CFU/100 mL.
200 CFU/100 mL (human contact waters)
40 ppb (µg/L)
Chlorophyll a
_____________________________________________________________________
CFU = colony-forming units
mg/L = milligrams per liter = parts per million
µg/L = micrograms per liter = parts per billion
96
19.0 Appendix B. UNCW ratings of sampling stations in Wilmington and New Hanover
County tidal creek watersheds based on August 2005 – July 2006 data for tidal creeks
and January -September 2006 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
Barnard’s Creek
BNC-RR
G
P
G
F
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
P
G
F
G
G
G
G
G
G
G
P
P
P
P
F
P
G
Burnt Mill Creek
BMC-KA1
BMC-KA3
BMC-AP1
BMC-AP3
BMC-WP
BMC-PP
G
G
G
G
G
P
P
P
F
G
P
P
F
G
G
G
G
G
P
P
P
P
P
P
Futch Creek
FC-4
FC-6
FC-8
FC-13
FC-17
FOY
G
G
G
G
G
G
G
F
F
F
F
F
G
G
G
G
F
G
G
G
G
F
P
G
Greenfield Lake
GL-LC
GL-JRB
GL-LB
GL-2340
GL-YD
GL-P
F
G
G
P
P
P
P
P
P
P
F
G
F
G
G
G
G
G
P
P
P
P
G
F
Turbidity
Fecal coliforms*
97
Watershed
Station
Chlor a
DO
Hewletts Creek
HC-2
HC-3
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
F
G
P
F
P
P
G
F
G
G
G
G
G
G
G
G
G
G
P
P
P
P
P
Howe Creek
HW-M
HW-FP
HW-GC
HW-GP
HW-DT
G
G
G
G
G
G
G
F
F
F
G
G
G
G
G
G
G
G
P
P
Motts Creek
MOT-RR
G
P
G
P
Pages Creek
PC-M
PC-BDDS
PC-BDUS
G
G
G
G
F
F
G
G
G
-
Smith Creek
SC-23
SC-CH
F
G
P
P
G
G
P
P
Whiskey Creek
Turbidity
Fecal coliforms*
WC-NB
G
F
G
WC-SB
G
G
G
WC-MLR
G
F
G
WC-AB
G
F
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.
98
20.0 Appendix C. GPS coordinates for New Hanover County Tidal Creek stations and
the Wilmington Watersheds Project sampling stations.
_____________________________________________________________________
Watershed
Station
GPS coordinates
Barnard’s Creek
BNC-TR
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
99
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
_____________________________________________________________________
100
21.0 Appendix D. University of North Carolina at Wilmington reports and papers
concerning water quality in New Hanover County’s tidal creeks.
Reports
Merritt, J.F., L.B. Cahoon, J.J. Manock, M.H. Posey, R.K. Sizemore, J. Willey and W.D.
Webster. 1993. Futch Creek Environmental Analysis Report. Center for Marine
Science Research, University of North Carolina at Wilmington, Wilmington, N.C.
Mallin, M.A., L.B. Cahoon, E.C. Esham, J.J. Manock, J.F. Merritt, M.H. Posey and R.K.
Sizemore. 1994. Water Quality in New Hanover County Tidal Creeks, 1993-1994.
Center for Marine Science Research, University of North Carolina at Wilmington,
Wilmington, N.C. 62 pp.
Mallin, M.A., L.B. Cahoon, J.J. Manock, J.F. Merritt, M.H. Posey, T.D. Alphin and R.K.
Sizemore. 1995. Water Quality in New Hanover County Tidal Creeks, 1994-1995.
Center for Marine Science Research, University of North Carolina at Wilmington,
Wilmington, N.C. 67 pp.
Mallin. M.A., L.B. Cahoon, J.J. Manock, J.F. Merritt, M.H., Posey, R.K. Sizemore, T.D.
Alphin, K.E. Williams and E.D. Hubertz. 1996. Water Quality in New Hanover County
Tidal Creeks, 1995-1996. Center for Marine Science Research, University of North
Carolina at Wilmington, Wilmington, N.C. 67 pp.
Mallin, M.A., L.B. Cahoon, J.J. Manock, J.F. Merritt, M.H. Posey, R.K. Sizemore, W.D.
Webster and T.D. Alphin. 1998. A Four-Year Environmental Analysis of New
Hanover County Tidal Creeks, 1993-1997. CMSR Report No. 98-01, Center for
Marine Science Research, University of North Carolina at Wilmington, Wilmington,
N.C.
Mallin, M.A., L.B. Cahoon, J.J. Manock, J.F. Merritt, M.H. Posey, T.D. Alphin, D.C.
Parsons and T.L. Wheeler. 1998. Environmental Quality of Wilmington and New
Hanover County Watersheds, 1997-1998. CMSR Report 98-03. Center for Marine
Science Research, University of North Carolina at Wilmington, Wilmington, N.C.
Mallin, M.A., S.H. Ensign, D.C. Parsons and J.F. Merritt. 1999. Environmental Quality of
Wilmington and New Hanover County Watersheds, 1998-1999. CMSR Report No.
99-02. Center for Marine Science Research, University of North Carolina at
Wilmington, Wilmington, N.C.
Mallin, M.A., L.B. Cahoon, S.H. Ensign, D.C. Parsons, V.L. Johnson and J.F. Merritt.
2000. Environmental Quality of Wilmington and New Hanover County Watersheds,
1999-2000. CMS Report No. 00-02. Center for Marine Science, University of North
Carolina at Wilmington, Wilmington, N.C.
Mallin, M.A., L.B. Cahoon, M.H. Posey, L.A. Leonard, D.C. Parsons, V.L. Johnson, E.J.
Wambach, T.D. Alphin, K.A. Nelson and J.F. Merritt. 2002. Environmental Quality of
Wilmington and New Hanover County Watersheds, 2000-2001. CMS Report 02-01,
101
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.
Mallin, M.A. 2006. Wading in waste. Scientific American 294:52-59.
Mallin, M.A., L.B. Cahoon, M.H. Posey, V.L. Johnson, D.C. Parsons, T.D. Alphin, B.R.
Toothman, M.L. Ortwine and J.F. Merritt. 2006. Environmental Quality of Wilmington
and New Hanover County Watersheds, 2004-2005. CMS Report 06-01, 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.
102
Mallin, M.A., K.E. Williams, E.C. Esham and R.P. Lowe. 2000. Effect of human
development on bacteriological water quality in coastal watersheds. Ecological
Applications 10:1047-1056.
Mallin, M.A., L.B. Cahoon, R.P. Lowe, J.F. Merritt, R.K. Sizemore and K.E. Williams.
2000. Restoration of shellfishing waters in a tidal creek following limited dredging.
Journal of Coastal Research 16:40-47.
Mallin, M.A., J.M. Burkholder, L.B. Cahoon and M.H. Posey. 2000. The North and
South Carolina coasts. Marine Pollution Bulletin 41:56-75.
Mallin, M.A., S.H. Ensign, M.R. McIver, G.C. Shank and P.K. Fowler. 2001.
Demographic, landscape, and meteorological factors controlling the microbial
pollution of coastal waters. Hydrobiologia 460:185-193.
Mallin, M.A., S.H. Ensign, T.L.Wheeler and D.B. Mayes. 2002. Pollutant removal
efficacy of three wet detention ponds. Journal of Environmental Quality 31:654-660.
Posey, M.H., T.D. Alphin, L.B. Cahoon, D.G. Lindquist, M.A. Mallin and M.E. Nevers.
2002, Resource availability versus predator control: questions of scale in benthic
infaunal communities. Estuaries 25:999-1014.
Cressman, K.A., M.H. Posey, M.A. Mallin, L.A. Leonard and T.D. Alphin. 2003. Effects
of oyster reefs on water quality in a tidal creek estuary. Journal of Shellfish Research
22:753-762.
Mallin, M.A. and A.J. Lewitus. 2004. The importance of tidal creek ecosystems. Journal
of Experimental Marine Biology and Ecology 298:145-149.
Mallin, M.A., D.C. Parsons, V.L. Johnson, M.R. McIver and H.A. CoVan. 2004. Nutrient
limitation and algal blooms in urbanizing tidal creeks. Journal of Experimental
Marine Biology and Ecology 298:211-231.
Nelson, K.A., L.A. Leonard, M.H. Posey, T.D. Alphin and M.A. Mallin. 2004.
Transplanted oyster (Crassostrea virginica) beds as self-sustaining mechanisms for
water quality improvement in small tidal creeks. Journal of Experimental Marine
Biology and Ecology 298:347-368.
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.