1999-2000 Final Report ENVIRONMENTAL QUALITY OF WILMINGTON AND NEW HANOVER COUNTY WATERSHEDS
1999-2000
by
Michael A. Mallin, Lawrence B. Cahoon, Scott H. Ensign, Douglas C. Parsons, Virginia L. Johnson and James F. Merritt
CMS Report 00-02 Center for Marine Science University of North Carolina at Wilmington Wilmington, N.C. 28409
December, 2000
Funded by: City of Wilmington
New Hanover County
Northeast New Hanover Conservancy
Executive Summary
This report represents combined results of Year 7 of the New Hanover County
Tidal Creeks Project and Year 3 of the Wilmington Watersheds Project. Water quality data are presented from a watershed perspective, regardless of political boundaries. The combined programs involved twelve watersheds and 54 sampling stations.
Barnards Creek – There was a general fecal coliform bacterial pollution problem throughout the Barnards Creek watershed. A station at Titanium Road (Independence Road Extention) was formerly thought to be an unimpacted control site. However, recently it has experienced high fecal coliform counts and occasional low dissolved oxygen problems, possibly as a result of nearby road construction and land clearing
activities. Lower Barnard’s Creek at River Road had occasional poor water quality as judged by turbidity, dissolved oxygen, and fecal coliform counts. Incoming and outflowing water at the wet detention pond on Echo Farms Golf course were sampled, with orthophosphate, conductivity and pH all significantly higher in the stream exiting the course. Other nutrients were somewhat higher in waters exiting the course than in the
inflowing waters. However, the concentrations of those nutrients were low in comparison to other area golf courses sampled, possibly because of nutrient uptake in a natural wetland through which the outfall stream passes before leaving the course. Bradley Creek – Unlike previous years, turbidity was not problematic during 1999-2000.
Low dissolved oxygen was an occasional problem in brackish waters of the creek during summer. Elevated nitrogen and phosphorus levels enter the creek in both the north and south branches, but algal blooms were not a problem during 1998-1999. Fecal coliforms were sampled only at the station at College Acres, which proved to be contaminated on 67% of the occasions sampled.
Burnt Mill Creek – A sampling station on Burnt Mill Creek at Princess Place had substandard dissolved oxygen during 42% of the sampling trips. This station also had poor microbiological water quality, exceeding the standard for human contact in nine of 12 samples. The effectiveness of Ann McCrary wet detention pond on Randall Parkway
as a pollution control device improved over last year. The pond led to significant reductions in ammonium, nitrate, conductivity and fecal coliform bacteria levels. However, all water quality parameters indicated a subsequent worsening of the creek from where it exited the pond to the downstream Princess Place sampling station.
Futch Creek – Futch Creek maintained good microbiological water quality, as it has since channel dredging at the mouth occurred in 1995 and 1996. Algal blooms were not a problem in 1999-2000. Periodic low summer dissolved oxygen concentrations occurred creekwide, as have occurred in previous years. Turbidity was a problem only in mid-creek stations.
Greenfield Lake – The three tributaries of Greenfield Lake (near Lake Branch Drive, Jumping Run Branch, and Lakeshore Commons Apartments) all suffered from low dissolved oxygen problems on numerous occasions. All three of these tributaries also
had frequent high fecal coliform counts, and maintained geometric mean counts in
excess of the state standard for human contact waters. The stream near Lakeshore Commons also maintained high nitrate and phosphate concentrations. Stations within the lake all experienced algal blooms at times, with a particularly dense bloom of the blue-green alga Anabaena cylindrical occurring in May and June 2000. Generally,
nutrient loading was highest at a station (GL-2340) located in the south end that
receives several urban and suburban inputs. Fecal coliform bacterial contamination was prevalent at all in-lake and tributary stations during 1999-2000, at levels generally higher than in 1998-1999. A large regional wet detention pond on the tributary Silver Stream did a very
good job of reducing pollutant loads to the lake from this drainage. Statistically
significant reductions in nitrate, total nitrogen, orthophosphate, total phosphorus, conductivity, and fecal coliform bacteria were all realized. The design of this pond consists of two interconnected basins containing large amounts of diverse aquatic vegetation, with most inputs directed into the upper basin. This could serve as a
potential model for future large pond design.
Hewletts Creek – This creek received high nutrient loading in its three upper branches, with one large algal bloom occurring in the north branch near Greenville Loop Road. The middle branch had the highest nutrient concentrations, largely derived from two golf
courses. Low dissolved oxygen occurred periodically in all of the tributary stations.
Howe Creek – Lower Howe Creek near the ICW maintained generally good water quality. Nutrient loading and algal bloom problems were most severe particularly upstream of the Graham Pond input area, with chlorophyll a concentrations at HW-DT
at or exceeding the sate standard of 40 µg/L four times during the year. Turbidity and low dissolved oxygen were problems in the upper areas of Howe Creek. Fecal coliform count data indicated microbiologically good water quality near the ICW but poor water quality near and upstream of the Graham Pond input area. Land clearing and
construction activities in the upper watershed are undoubtedly the cause of non-point
source pollution to the upper creek. Motts Creek – This creek was sampled at only one station, at River Road. Algal blooms and low dissolved oxygen were not problems here in 1999-2000. Turbidity was a
periodic problem and fecal coliform pollution a frequent problem at this station.
Pages Creek – This creek maintained generally good water quality during 1999-2000. Nutrient loading and phytoplankton growth was low, even at the most anthropogenically-impacted stations. However, there was periodic hypoxia in warmer months, particularly
at a station draining lower Bayshore Drive (PC-BDDS -hypoxia on three of 12 sampling
occasions).
Smith Creek – Turbidity was not a major problem at the two stations sampled in this watershed, in contrast to previous years. Completion of highway construction and natural revegetation of ditched and drained wetlands near Smith Creek parkway were
likely mitigating factors to this reduction of turbidity. Nutrient concentrations were
elevated in the creek compared with most other nearby watershed sites, but algal blooms were not a problem in Smith Creek. However, fecal coliform bacterial counts exceeded the state standard for human contact waters at both sites on a number of occasions. Low dissolved oxygen problems were frequent in Smith Creek during 1999-
2000. Upper and Lower Cape Fear Watersheds – Water quality at the one station on the stream draining the Upper Cape Fear watershed (behind the Wilmington police station) had high nitrate concentrations, although they were lower than in previous years. Fecal
coliform concentrations exceeded the state standard for human contact waters at both
this station and the station draining Greenfield Lake during 1999-2000. Whiskey Creek – Whiskey Creek had relatively high nutrient loading but generally low chlorophyll a concentrations in 1999-2000. Most stations had acceptable dissolved
oxygen and turbidity concentrations. However, fecal coliform counts indicated unsafe
shellfishing waters throughout the creek, and unsafe water for human contact at the upper feeder stream stations. Use Support Ratings – The NC Division of Water Quality utilizes an EPA-based system
to determine if a water body supports its designated use (described in Appendix B). We applied these standards to the water bodies described in this report, based on 1999-2000 data. Our analysis shows that (based on fecal coliform standards for human contact waters) all of upper Barnards Creek was non-supporting while lower Barnard’s Creek is partially supporting. All of Burnt Mill Creek was non-supporting in 1999-2000.
Futch Creek is fully supporting for fecal coliform bacteria, including for shellfishing in the lower four stations. Greenfield Lake and its tributaries were non-supporting throughout. Upper Howe Creek was non-supporting while lower Howe Creek was fully supporting for human contact. Lower Motts Creek was non-supporting, one of the Smith Creek stations was non-supporting and the other was partially supporting. Both the Upper and
Lower Cape Fear stations were non-supporting. Whiskey Creek is fully supporting for human contact in the lower creek but non-supporting in the upper creek; this creek is non-supporting for shellfishing throughout. We also list support categories for dissolved oxygen and turbidity in Appendix B.
Table of Contents 1.0 Introduction 1
1.1 Methods 1 2.0 Barnards Creek 3
3.0 Bradley Creek 6
4.0 Burnt Mill Creek 9 5.0 Futch Creek 12
6.0 Greenfield Lake 15 7.0 Hewletts Creek 19
8.0 Howe Creek 22
9.0 Motts Creek 26 10.0 Pages Creek 29
11.0 Smith Creek 31 12.0 Upper and Lower Cape Fear 34
13.0 Whiskey Creek 36
14.0 Rainfall Effects on Silicate Loading to Tidal Creeks 40 15.0 References Cited 45
16.0 Acknowledgments 47 17.0 Appendix A: Selected N.C. water quality standards 48
18.0 Appendix B: Water Body Use Support Rankings
Based on DWQ Chemical Standards 49 19.0 Appendix C: UNCW reports related to tidal creeks 51
Cover: A Global View of Howe Creek (by Scott Ensign)
1.0 Introduction Since 1993, scientists at the UNC Wilmington Center for Marine Science
Research have been studying five tidal creeks in New Hanover County. This project,
funded by New Hanover County, the Northeast New Hanover Conservancy, and UNCW, yielded a comprehensive report detailing important findings from 1993-1997, and produced a set of management recommendations for improving creek water quality (Mallin et al. 1998a).
Additionally, in October 1997 the Center for Marine Science Research began a project (funded by the City of Wilmington Engineering Department) with the goal of assessing water quality in Wilmington City watersheds under base flow conditions. Additionally, certain sites were analyzed for sediment heavy metals concentrations
(EPA Priority Pollutants). In the past two years we have produced combined Tidal
Creeks – Wilmington City Watersheds reports (Mallin et al. 1998b; 1999). In the present report we present results of continuing studies from 1999-2000 in the tidal creek complex and the City of Wilmington watersheds.
The water quality data within is presented from a watershed perspective. Some
of the watersheds cross political boundaries (i.e. parts of the same watershed may lie in the County but not the City). Bradley and Hewletts Creeks are examples. Water quality parameters analyzed in the tidal creeks include water temperature, pH, dissolved oxygen, salinity/conductivity, turbidity, nitrate, ammonium, orthophosphate, chlorophyll
a, and in selected creeks fecal coliform bacteria. Similar analyses were carried out in
the City watersheds with the addition of total Kjeldahl nitrogen, total nitrogen (TN), total phosphorus (TP), and suspended solids. In 1999-2000 Whiskey Creek was added to the matrix of watersheds analyzed by our combined programs.
1.1 Methods
Field parameters were measured at each site using a YSI 6920 Multiparameter Water Quality Probe (sonde) linked to a YSI 610 display unit. Individual probes within the instruments measured water temperature, pH, dissolved oxygen, turbidity, salinity,
and conductivity. YSI Model 85 and 55 dissolved oxygen meters were also used on
occasion. The instruments were calibrated prior to each sampling trip to ensure accurate measurements. For the six tidal creeks, water samples were collected monthly, at or near high
tide. For nitrate+nitrite (hereafter referred to as nitrate) and orthophosphate
assessment, three replicate acid-washed 125 mL bottles were placed ca. 10 cm below the surface, filled, capped, and stored on ice until processing. In the laboratory the triplicate samples were filtered simultaneously through 1.0 micrometer pore-sized .0glass fiber filters using a manifold with three funnels. The pooled filtrate was stored
frozen until analysis. Nitrate+nitrite and orthophosphate were analyzed using a
Technicon AutoAnalyzer following EPA protocols. Samples for ammonium were collected in duplicate, field-preserved with phenol, stored on ice, and analyzed in the laboratory according to the methods of Parsons et al. (1984). Fecal coliform samples were collected by filling pre-autoclaved containers ca. 10 cm below the surface, facing
into the stream. Samples were stored on ice until processing (< 6 hr). Fecal coliform
concentrations were determined using a membrane filtration (mFC) method (APHA 1995). North Carolina water quality standards relevant to this report are listed in Appendix A.
The analytical method used to measure chlorophyll a is described in Welschmeyer (1994) and US EPA (1997). Chlorophyll a concentrations were determined directly from the 1.0 micron 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 for 24 hours. The acetone extracts the chlorophyll a from the glass filters into solution. Each solution was then analyzed for chlorophyll a concentrations using a Turner AU-10 fluorometer. This method uses an optimal combination of
excitation and emission bandwidths that reduces the errors inherent in the acidification
technique. Samples were collected monthly within the Wilmington City watersheds from August 1999 through July 2000. Field measurements were taken as indicated above.
Nutrients (nitrate, ammonium, total Kjeldahl nitrogen (TKN), total nitrogen (TN),
orthophosphate, and total phosphorus (TP)) and total suspended solids (TSS) were analyzed by a state-certified contract laboratory using EPA and APHA techniques. We also computed inorganic nitrogen to phosphorus molar ratios for relevant sites (N/P). Chlorophyll a was run at UNCW-CMS as described above.
For three detention ponds (Ann McCrary Pond on Burnt Mill Creek, Silver Stream Pond in the Greenfield Lake watershed, and the main pond on Echo Farms Golf Course in the Barnards Creek watershed) we were able to obtain data from input (control) and outfall stations. We used these data to test for statistically significant differences in
pollutant concentrations between pond input and output stations. The data were first
tested for normality using the Shapiro-Wilk test. Normally distributed data parameters were tested using the paired-difference t-test, and non-normally distributed data parameters were tested using the Wilcoxon Signed Rank test. Statistical analyses were conducted using SAS (Schlotzhauer and Littell 1987).
2.0 Barnards Creek The water quality of lower Barnard’s Creek is becoming an important issue as a
major housing development is commencing construction activities in the area east of
River Road and between Barnard’s and Mott’s Creeks. We report collected data at a station located on Barnard’s Creek at River Road (BC-RR) that drains part of this area. The BNC-TR site in Barnard’s Creek watershed drains a wooded area and had been considered a control site for nutrients and physical parameters (Fig.2.1). However, we
also note that the control is now near an active road and condominium construction
area on Titanium Road, or Independence Road Extension (Fig. 2.1). Fecal coliform bacterial counts at BNC-TR have increased considerably relative to the 1997-1998 period (Mallin et al. 1998b; 1999). The BNC-CB site is near Carolina Beach Road and drains an area hosting construction activities. Both BNC-TR and BNC-CB can be
considered impaired by fecal coliform loading (Table 2.1; Appendix B). During this
sampling period there was little difference between these two sites in concentrations of most parameters; however, TP and ammonia are higher at BNC-CB than at the control site.
The Barnard’s Creek watershed hosts the Echo Farms Country Club. Much of
the course drainage enters a large (1.75 acre) pond, which discharges through a wooded wetland. We sampled a pond input station draining a suburban area (BNC-EF) and the pond outflow exiting the riparian wetland (BNC-AW). A primary goal was to assess the efficacy of golf course nutrient removal by this pond during the period
August 1999 – July 2000. Golf course loading led to significant increases in
orthophosphate and TP, among nutrients (Table 2.2), whereas last year increases were seen only in orthophosphate. There were input-output increases in conductivity, as well (Fig. 2.2). We also point out that overall concentrations of inorganic nutrients in the output stream were low in comparison with output from other area golf courses (Mallin
and Wheeler 2000). The design of a wet detention pond followed by a natural wetland
area does a good job of keeping nutrient concentrations low in the course outfall. We report here water quality data from the estuarine site on River Road. BNC-RR had average salinity of 4.3 ppt with a range of 0.1-16.3 ppt. Lower Barnard’s Creek
had dissolved oxygen levels below 5 ppm on two occasions out of 12 samples in 1999-
2000, for a 17% non-compliance rate. Turbidity on average was moderately high (30 NTU), above the state standard for estuarine waters of 25 NTU. The standard was exceeded 50% of the time during 1999-2000. Fecal coliform counts exceeded the state standard three of 12 occasions for a 25% non-compliance rate. Thus, this station can
be considered impaired by turbidity and fecal coliform loading, with periodic low
dissolved oxygen problems.
Table 2.1. Mean and standard deviation of water quality parameters in Barnard’s Creek watershed, August 1999-July 2000. Fecal coliforms as geometric mean; N/P ratio as median.
_____________________________________________________________________
Parameter BNC-TR BNC-CB BNC-RR _____________________________________________________________________ DO (mg/L) 6.5 (1.6) 7.3 (1.5) 7.5 (1.9)
Turbidity (NTU) 7.7 (9.4) 10.5 (3.0) 29.8 (17.6)
TSS (mg/L) 3.9 (2.4) 3.9 (1.6) 29.4 (23.6) Nitrate (mg/L) 0.093 (0.106) 0.108 (0.077) 0.238(0.175) Ammon. (mg/L) 0.035 (0.029) 0.084 (0.058) 0.053 (0.053) TN (mg/L) 0.389 (0.219) 0.404 (0.194) 0.753(0.296)
Phosphate (mg/L) 0.023 (0.014) 0.018 (0.009) 0.078 (0.029)
TP (mg/L) 0.042 (0.030) 0.096 (0.241) 0.163 (0.068) N/P molar ratio 11.1 19.9 7.5
Chlor. a (µg/L) 0.7 (0.4) 1.7 (0.7) 2.6 (2.6)
Fec. col.(/100 mL) 336 238 102
_____________________________________________________________________ Table 2.2 Mean and standard deviation of water quality parameters in Barnard’s Creek watershed, including a comparison of pollutant concentrations in input (BNC-EF) and
output (BNC-AW) waters of wet detention pond on Echo Farms Country Club, August
1999-July 2000. _____________________________________________________________________ Parameter BNC-EF BNC-AW _____________________________________________________________________
DO (mg/L) 6.0 (1.6) 5.8 (2.1)
Cond. (µS/cm) 153 (25) 871 (1498)** pH 6.8 (0.6) 6.9 (0.4) Turbidity (NTU) 2.6 (1.5) 4.1 (2.4) TSS (mg/L) 5.0 (7.3) 4.8 (3.8)
Nitrate (mg/L) 0.101 (0.104) 0.126 (0.155)
Ammon. (mg/L) 0.032 (0.024) 0.043 (0.023) TN (mg/L) 0.382 (0.198) 0.662 (0.746) Phosphate (mg/L) 0.023 (0.014) 0.038 (0.023)** TP (mg/L) 0.030 (0.018) 0.072 (0.051)**
N/P molar ratio 12.0 6.9
Chlor. a (µg/L) 2.2 (2.1) 2.9 (3.3) Fec. col.(/100 mL) 128 137 _____________________________________________________________________
* Indicates significant difference between input and output concentration at p<0.05
**Indicates significant difference between input and output concentration at p<0.01
3.0 Bradley Creek The Bradley Creek watershed is of particular current interest as a principal
location for Clean Water Trust Fund mitigation activities, including the purchase and
renovation of Airlie Gardens by the County. This creek is one of the most polluted in New Hanover County, particularly by fecal coliform bacteria (Mallin et al. 2000). Seven stations were sampled in the past year, both fresh and brackish (Fig. 3.1).
In contrast to the previous two years, turbidity was not a problem during 1999-
2000 (Table 3.1). Completion of the wet detention pond and cessation of road construction (Eastwood Road) led to large decreases in turbidity in the north branch of the creek, particularly at BC-NBU (Table 3.1). In summer the downstream brackish stations periodically had hypoxic (< 5.0 mg/L) dissolved oxygen conditions. BC-CA had
substandard dissolved oxygen conditions on three of 12 sampling occasions. Only one
station was sampled for fecal coliform concentrations last year (BC-CA – the creek as it passes beneath College Acres). This station had a geometric mean concentration of 616 CFU/100 mL, with a range of 52 – 15,000. Fecal coliforms exceeded the state human contact standard of 200 CFU/100 mL on eight of 12 occasions, a 67% non-
compliance rate (Appendix B).
Table 3.1 Parameter concentrations at Bradley Creek sampling stations, 1999-2000. Data as mean (SD) / range. _____________________________________________________________________
Station Salinity (ppt) Turbidity (NTU) Dissolved Oxygen (mg/L)
_____________________________________________________________________ BC-76 31.6 (3.2) 6.2 (2.7) 6.7 (2.3) 23.8-35.6 1.9-12.9 2.9-10.3
BC-SB 8.3 (8.5) 11.6 (4.3) 6.9 (2.5) 0.2-23.1 3.6-20.5 3.0-10.3 BC-SBU 0.1 (0.0) 6.5 (3.0) 6.6 (1.8)
0.1-0.2 3.0-12.9 3.4-8.9
BC-NB 24.4 (9.3) 10.6 (3.8) 6.4 (2.5) 1.5-32.6 5.8-17.6 2.6-11.7
BC-NBU 0.1 (0.1) 6.4 (2.2) 7.6 (0.9)
0.1-0.2 1.4-10.0 6.2-9.8 BC-CR 0.1 (0.0) 7.7 (16.2) 7.2 (1.1) 0.0-0.1 0.5-58.0 4.9-8.7
BC-CA 0.1 (0.1) 10.7 (14.5) 6.1 (1.1) 0.1-0.1 3.0-55.0 4.7-7.9 _____________________________________________________________________
Nitrate concentrations were highest at stations BC-CR (draining a suburban residential area along Clear Run Drive) and BC-SBU (upper south branch) and BC-CA (draining apartment complexes, construction areas, and retail establishments
upstream). Particularly high orthophosphate levels were found at BC-CA, with
somewhat elevated orthophosphate levels at BC-SB, BC-SBU and BC-NB (Table 3.2). Ammonium was also elevated at BC-CA. In contrast to previous years (Mallin et al. 1998a; 1998b) Bradley Creek was relatively free of algal blooms in 1999-2000 (Table 3.2). Median inorganic molar N/P ratios were 5.9 for BC-76, 21.2 for BC-SB, and 9.1 for
BC-NB. This indicates that phytoplankton growth was likely nitrogen limited at BC-76
and BC-NB, but phosphorus limited at BC-SB. Last year (1998-1999) the ratios indicated that phytoplankton growth at all three stations was likely nitrogen-limited, but in 1997-1998 very high N/P ratios prevailed in the two tributary stations, indicating possible phosphorus limitation.
Table 3.2. Nutrient and chlorophyll a data at Bradley Creek sampling stations, 1999-
2000. Data as mean (SD) / range, nutrients in mg/L, chlorophyll a as µg/L. _____________________________________________________________________
Station Nitrate Ammonium Orthophosphate Chlorophyll a
_____________________________________________________________________ BC-76 0.010 (0.006) 0.018 (0.023) 0.008 (0.003) 1.3 (0.4) 0.005-0.023 0.005-0.063 0.004-0.016 0.6-2.1
BC-SB 0.072 (0.058) 0.036 (0.033) 0.011 (0.007) 8.4 (10.7) 0.001-0.176 0.007-0.114 0.005-0.033 1.0-36.0 BC-SBU 0.143 (0.064) NA 0.011 (0.011) 3.1 (4.1)
0.033-0.255 0.005-0.045 0.2-12.7
BC-NB 0.028 (0.051) 0.032 (0.028) 0.010 (0.005) 3.5 (5.4) 0.002-0.187 0.005-0.069 0.005-0.019 0.7-20.3
BC-NBU 0.128 (0.056) NA 0.004 (0.004) 2.1 (4.1)
0.072-0.281 0.001-0.016 0.1-14.7 BC-CR 0.268 (0.076) NA 0.007 (0.004) 1.4 (1.5) 0.176-0.480 0.003-0.017 0.1-4.8
BC-CA 0.222 (0.150) 0.098 (0.099) 0.038 (0.020) 7.8 (9.1) 0.005-0.490 0.005-0.390 0.010-0.090 1.6-27.3 _____________________________________________________________________
4.0 Burnt Mill Creek The Burnt Mill Creek watershed was sampled just upstream of Ann McCrary
Pond on Randall Parkway (AP1), along shore at mid-pond (AP2), about 40 m
downstream of the pond outfall (AP3), and in the creek from the bridge at Princess Place (BMC-PP - Fig. 4.1). Ann McCrary Pond is a large (28.8 acres) regional wet detention pond draining 1,785 acres, with a recently constructed apartment complex at the upper end near AP1. The pond itself usually maintains a thick growth of submersed
aquatic vegetation, particularly Hydrilla verticillata, Egeria densa, Alternanthera
philoxeroides, Ceratophyllum demersum and Valliseneria americana. A survey in late summer 1998 indicated that approximately 70% of the pond area was vegetated. There have been efforts to control this growth, including addition of triploid grass carp as grazers. Our survey also found that this pond is host to Lilaeopsis carolinensis, which is
a threatened plant species in North Carolina.
Turbidity and suspended solids concentrations were low, in contrast to earlier years (1997-1998), likely as a result of cessation of the extensive apartment construction and land-clearing activities that began early in this study. Fecal coliform
concentrations entering Ann McCrary Pond at AP1 were very high, however (Table 4.1),
possibly a result of increased pet waste runoff from the apartment complex. It is notable that as construction ceased and apartment habitation began, turbidity decreased while fecal coliform counts increased (Mallin et al. 1998b; 1999). The efficiency of this pond as a pollutant removal device was mixed. Fecal coliforms were significantly reduced
during passage through the pond (Table 4.1). Total suspended solids and turbidity
were low entering the pond this year and there was no significant difference in removal of these two parameters. There were no statistically significant increases or decreases in nutrients during passage through the pond this year (Table 4.1). As in previous years, it is likely that inputs of nutrients have entered the pond from suburban drainage
stream midway down the pond across from our AP2 site. Also, intensive waterfowl use
of the pond, particularly at a tributary near the outfall, may have contributed to nutrient loading in the pond and along its shoreline. This year highest nitrogen concentrations were found at AP1, and highest phosphorus concentrations at AP3 (Table 4.1). There was a significant decrease in conductivity through the pond. Dissolved oxygen
significantly increased through the pond, probably because of in-pond photosynthesis
and aeration by passage over the final dam at the outfall. There was a significant increase in pH as well, probably due to utilization of CO2 during photosynthesis in the pond.
The Princess Place location experienced some water quality problems during the sample period (Appendix B). Dissolved oxygen was substandard on five of 12 sampling trips, for a non-compliance rate of 42%. The most important issue, from a public health perspective, was the excessive fecal coliform counts, which maintained a geometric mean (585 CFU/100 mL) well in excess of the state standard for human contact waters
(200 CFU/100 mL). Fecal coliform counts were greater than 200 CFU/100 mL in nine of 12 samples, or 75% of the time. It is notable that phosphorus concentrations increased considerably along the passage from BMC-AP3 to the Princess Place location, and nitrogen concentrations were similar between the two stations (Table 4.1).
This creek was strongly impacted by fecal coliform loading as a result of Hurricane Floyd. Average counts for the four stations on September 22 1999 were 12,125 CFU/100 mL, with individual station counts as follows: AP1=22,000,
AP2=14,000, AP3=6,000 and BMC-PP=6,500. The count at AP1 was also the highest
individual station count in the entire Wilmington-New Hanover County watershed system during 1999-2000. Hurricane Irene elevated bacterial pollution as well, with average watershed counts of 3,600 CFU/100 mL and the highest individual station being BMC-PP with 13,000 CFU/100 mL. Some of this pollution may have derived from
overloaded sewage systems and some from heavy rainfall-driven urban runoff. This
creek has been targeted for stream restoration by the North Carolina Wetlands Restoration Program, with preliminary work beginning in late 2000. Table 4.1. Mean and (standard deviation) of water quality parameters in Burnt Mill
Creek watershed, 1999-2000. Fecal coliforms given as geometric mean; N/P ratio as
median. _____________________________________________________________________ Parameter BMC-AP1 BMC-AP2 BMC-AP3 BMC-PP _____________________________________________________________________
DO (mg/L) 6.7 (1.6) 8.3 (3.0) 9.6 (1.8)** 5.0 (2.0)
Cond. (µS/cm) 256 (20) 225 (35) 224 (45)* 333 (35) pH 6.4 (0.5) 6.9 (0.9) 7.2 (1.0)** 6.8 (0.5) Turbidity (NTU) 7.4 (4.2) 7.6 (4.6) 5.9(4.2) 17.1 (38.8)
TSS (mg/L) 2.5 (1.9) 5.0 (3.2) 3.2 (2.5) 4.9 (2.2)
Nitrate (mg/L) 0.350 (0.614) 0.159 (0.185) 0.300 (0.763) 0.277 (0.260) Ammonium (mg/L) 0.133 (0.229) 0.065 (0.058) 0.067 (0.079) 0.063 (0.032) TN (mg/L) 0.837 (0.948) 0.583 (0.318) 0.627 (0.744) 0.638 (0.352) Phosphate (mg/L) 0.018 (0.008) 0.018 (0.010) 0.024 (0.014) 0.038 (0.020)
TP (mg/L) 0.037 (0.020) 0.038 (0.018) 0.058 (0.051) 0.079 (0.033)
N/P molar ratio 32.1 24.4 10.5 20.2 Fec. col. (/100 mL) 569 197 114* 585
Chlor. a (µg/L) 1.2 (0.9) 3.3 (1.9) 3.4 (2.8) 2.9 (2.0)
_____________________________________________________________________
* Indicates statistically significant difference between AP1 and AP3 at p<0.05
**Indicates statistically significant difference between AP1 and AP3 at p<0.01
5.0 Futch Creek During 1995 and 1996 two channels were dredged in the mouth of Futch Creek
(Fig. 5.1) to improve circulation and hopefully reduce fecal coliform bacterial
concentrations. There was a statistically significant increase in salinity in the creek in the months following dredging, significantly lower fecal coliform counts, and the lower creek was reopened to shellfishing (Mallin et al. 2000b). During the past year’s sampling two stations, FC-2 and FC-20, were dropped from the sampling scheme.
None of the creek stations had average turbidity exceeding the state standard of 25
NTU, and there were seven incidents where readings exceeded the turbidity standard. The months of August 1999 and June 2000 were characterized by incidences of substandard dissolved oxygen at most of the stations.
Table 5.1. Physical parameters at Futch Creek sampling stations, 1999-2000. Data
given as mean (SD) / range. _____________________________________________________________________ Station Salinity (ppt) Turbidity (NTU) Dissolved oxygen (mg/L) _____________________________________________________________________
FC-4 33.3 (1.8) 10.8 (7.0) 7.3 (1.8) 29.1-35.9 3.3-21.2 4.3-10.5 FC-6 31.9 (1.7) 9.1 (4.1) 7.1 (2.0)
28.1-34.8 3.3-14.8 3.8-10.8
FC-8 30.6 (2.1) 14.2 (13.5) 6.8 (1.8) 27.1-33.2 5.7-46.7 3.3-9.7
FC-13 24.8 (2.9) 14.3 (10.2) 6.6 (1.9)
19.8-29.4 3.8-29.0 2.8-9.2 FC-17 19.8 (4.9) 16.0 (14.6) 6.6 (1.8) 10.1-26.6 5.3-43.7 3.0-8.5
FOY 24.3 (3.4) 8.5 (4.9) 6.9 (2.1) 18.4-29.4 3.6-17.6 3.4-9.8 _____________________________________________________________________
Nutrient concentrations in Futch Creek were generally low, with the exception of
periodic nitrate pulses in the upper stations FC-17 and FC-20 (Table 5.2). The source of these pulses has been identified as groundwater inputs entering the marsh in springs between FC-19 and FC-13 (Mallin et al. 1998b). The creek was free from algal blooms during our sampling visits (Table 5.2), even in the upper stations. Computed median
inorganic N/P molar ratios were 4.4 for FC-4 (indicating potential N limitation of
phytoplankton growth), but 21.6 and 23.0 for FC-17 and FOY, respectively (indicating potential P limitation of phytoplankton growth). N/P expressed no particular seasonality over the year.
Table 5.2. Nutrient and chlorophyll a data at Futch Creek sampling stations, 1999-
2000. Data as mean (SD) / range, nutrients in mg/L, chlorophyll a as µg/L.
_____________________________________________________________________
Station Nitrate Ammonium Orthophosphate Chlorophyll a _____________________________________________________________________ FC-4 0.006 (0.005) 0.027 (0.053) 0.006 (0.002) 1.2 (1.0)
0.001-0.013 0.001-0.140 0.003-0.010 0.3-3.6
FC-6 0.012 (0.009) NA 0.007 (0.002) 1.4 (1.3) 0.002-0.031 0.005-0.010 0.3-4.6
FC-8 0.018 (0.013) NA 0.008 (0.002) 1.7 (1.7)
0.004-0.050 0.006-0.011 0.3-5.7 FC-13 0.064 (0.046) NA 0.009 (0.004) 3.2 (3.4) 0.003-0.130 0.003-0.016 0.5-12.1
FC-17 0.107 (0.093) 0.022 (0.024) 0.013 (0.004) 13.3 (31.0) 0.019-0.272 0.001-0.068 0.007-0.018 0.5-106.1 FOY 0.052 (0.037) 0.028 (0.026) 0.009 (0.003) 3.0 (3.2)
0.007-0.127 0.001-0.070 0.003-0.012 0.4-10.7
_____________________________________________________________________ As reportedly previously (Mallin et al. 2000b) the dredging experiment proved to be successful and the lower portion of the creek was reopened to shellfishing. During
1999-2000 the lower creek maintained excellent microbiological water quality for
shellfishing (Table 5.3). The mid-creek areas had good microbiological water quality as well, although geometric mean fecal concentrations increased somewhat compared with the previous year (Mallin et al. 1999). The uppermost stations continued to have fecal coliform bacterial concentrations well below those of the pre-dredging period.
Table 5.3. Futch Creek fecal coliform bacteria data, including percent of samples exceeding 43 CFU per 100 mL, 1999-2000. _____________________________________________________________________ Station FC-4 FC-6 FC-8 FC-13 FC-17 FOY ALL
Geomean 3 4 6 22 63 20 24 % > 43 /100ml 0 9 9 45 82 36 30 _____________________________________________________________________
6.0 Greenfield Lake One of the major pollution mitigation features in the Greenfield Lake watershed is
an extensive wet detention pond along the Silver Stream branch (Fig. 6.1). The pond
drains approximately 280.5 acres, of which about 43% is impervious surface area. The pond is divided into a 1.25 acre upper and a 1.48 acre lower basin by a causeway pierced by three pipes connecting the flow. In early summer 1998 approximately 70% of the upper pond was covered by a mixture of floating and emergent aquatic
macrophyte vegetation, with about 40% of the lower pond covered by vegetation.
Principal species in the upper basin were alligatorweed Alternanthera philoxeroides, pennywort Hydrocotyle umbellate, water primrose Ludwigia leptocarpa and cattail
Typha latifolia, while the lower basin vegetation was dominated by alligatorweed, water primrose, and cattail. This pond functioned very well as a nutrient removal system
(Table 6.1). Removal of orthophosphate (61%), nitrate (58%), TN (56%), TP (47%) and
ammonium (40%) was achieved. The decreases in nitrate, ammonium, TN, orthophosphate, TP, and conductivity were all statistically significant. Turbidity and TSS were generally low at both locations this past year, but there was a significant increase through the pond, probably as a result of significant phytoplankton increases (Table
6.1). Dissolved oxygen significantly increased, probably in part because of aeration
while passing through the outfall. Increased oxygenation through photosynthesis was likely an important factor as well. Passage through the pond reduced fecal coliform counts by 52%, but this was not statistically significant (Table 6.1). Pollutant removal efficiencies were generally good all around, but not as good as last year (Mallin et al.
1999).
Table 6.1. Comparison of pollutant concentrations in input (SS1) and output (SS2) waters of regional wet detention pond on Silver Stream, in Greenfield Lake watershed, August 1999 – July 2000.
_____________________________________________________________________
Parameter SS1 SS2 _____________________________________________________________________
DO (mg/L) 6.1 (1.9) 7.9 (2.0)**
Cond. (µS/cm) 206 (79) 161 (30)* pH 6.5 (0.4) 6.5 (0.5) Turbidity (NTU) 4.7 (7.2) 5.5 (3.1)**
TSS (mg/L) 2.3 (2.0) 4.1 (1.7)**
Nitrate (mg/L) 0.366 (0.276) 0.152 (0.132)* Ammonium (mg/L) 0.156 (0.331) 0.093 (0.196)* TN (mg/L) 1.694 (2.895) 0.747 (0.952)* Phosphate (mg/L) 0.071 (0.053) 0.028 (0.018)**
TP (mg/L) 0.138 (0.091) 0.073 (0.042)*
Chlorophyll a (µg/L) 2.4 (3.1) 8.2 (9.8)* Fecal col. (CFU/100 mL) 564 273 _____________________________________________________________________ * indicates significant difference between input and output concentration at p<0.05
**Indicates significant difference between input and output concentration at p<0.01
Three tributaries of Greenfield Lake were sampled for physical, chemical, and biological parameters (Table 6.2, Fig. 6.1). Two of the tributaries suffered from extreme hypoxia, with both GL-LB (creek at Lake Branch Drive) and GL-LC (creek beside
Lakeview Commons) showing average concentrations below the state standard (DO <
5.0 mg/L). Dissolved oxygen levels were substandard four of 12 times at GL-JRB, six of 12 times at GL-LC, and 11 of 12 times at GL-LB (Appendix B). Turbidity and suspended solids were generally low in the tributary stations (Table 6.2). Like last year, nitrate concentrations were highest at GL-LC, moderate at GL-LB and lowest at GL-JRB
(Table 6.3). Ammonium concentrations were generally similar across the three tributary
stations. Orthophosphate concentrations were highest at GL-LB, followed by GL-LC and GL-JRB. Overall, GL-LC maintained the highest nutrient concentrations of any of the input streams tested. All three of these input streams maintained fecal coliform levels indicative of poor water quality, with fecal coliform counts exceeding the state
standard for human contact waters (200 CFU/100 mL) 11 of 12 times at GL-LB, eight of
12 times at GL-LC, and six of 12 times at GL-JRB. Chlorophyll a levels were generally low in these streams (Table 6.3). Table 6.2. Mean and (standard deviation) of water quality parameters in tributary
stations of Greenfield Lake, 1999-2000. Fecal coliforms as geometric mean; N/P ratio
as median. _____________________________________________________________________ Parameter GL-JRB GL-LB GL-LC _____________________________________________________________________
DO (mg/L) 5.2 (2.5) 2.4 (1.5) 4.4 (1.5)
Turbidity (NTU) 12.7 (25.7) 7.2 (7.1) 3.3 (2.6) TSS (mg/L) 5.1 (2.6) 4.0 (2.1) 2.0 (1.8) Nitrate (mg/L) 0.203 (0.192) 0.170 (0.187) 0.368 (0.365) Ammonium (mg/L) 0.085 (0.075) 0.094 (0.059) 0.098 (0.136)
TN (mg/L) 0.707 (0.568) 0.862 (0.725) 0.808 (0.616)
Phosphate (mg/L) 0.033 (0.016) 0.047 (0.012) 0.043 (0.031) TP (mg/L) 0.115 (0.138) 0.103 (0.047) 0.228 (0.435) N/P molar ratio 21.9 10.5 19.0 Fec. col. (/100 mL) 336 581 457
Chlor. a (µg/L) 3.6 (2.2) 3.7 (3.3) 4.5 (8.8) _____________________________________________________________________ Three in-lake stations were sampled (Table 6.3). Station GL-2340 represents an
area receiving a considerable influx of urban/suburban runoff, GL-YD is downstream
and receives some outside impacts, and GL-P is at Greenfield Lake Park, away from inflowing streams but in a high-use waterfowl area (Fig. 6.1). Low dissolved oxygen was not an important factor at these stations during the sampling period. Turbidity and suspended solids were low at all three sites, except during the algal blooms. Fecal
coliform concentrations were worse than last year, and problematic at all three stations.
The annual geometric mean exceeded the state standard at both GL-2340 and GL-P (Table 6.3). At GL-2340 the state standard was exceeded on nine of 11 occasions, at GL-YD it was exceeded on four of 12 occasions, and at GL-P it was exceeded on eight of 12 occasions in 1999-2000. We note that the large waterfowl populations frequently
utilize some areas of the lake and may be a source of fecal coliform bacteria. Highest
monthly counts occurred in September 1999 following Hurricane Floyd, with a
watershed average of 10,300 CFU/100 ml. Counts in October were also elevated by Hurricane Irene with a watershed average of 3,100 CFU/100 mL. Sanitary sewer overflows and heavy urban runoff were the likely causes of these high counts.
Nitrate concentrations were relatively high at GL-2340, reflecting the proximity of three tributary streams. Nitrate levels decreased considerably toward the park (Table 6.3). Total nitrogen, ammonium, and orthophosphate at GL-P were higher than or approximately equal to concentrations at the other lake stations (Table 6.3); possibly
this is a result of nutrient loading from the abundant local waterfowl community.
Inorganic N/P molar ratios can be computed from ammonium, nitrate, and orthophosphate data and can help determine what the potential limiting nutrient can be in a water body. Ratios well below 16 (the Redfield ratio) can indicate potential nitrogen limitation, and ratios well above 16 can indicate potential phosphorus limitation (Hecky
and Kilham 1988). Based on the median N/P ratios (Table 6.3), phytoplankton growth
in Greenfield Lake should be primarily nitrogen-limited. Our previous bioassay work indicated that this was indeed the case (Mallin et al. 1999). Phytoplankton blooms are periodically problematic in Greenfield Lake, and
usually consist of green or blue-green algal species, or both together. These blooms
have occurred during all seasons, but are primarily a problem in spring and summer. In 1999-2000 an extensive blue-green algal bloom consisting of Anabaena cylindrica
occurred in May and June 2000, with chlorophyll a ranging from 59 – 119 µg/L at
Stations GL-YD and GL-P. Another bloom occurred in August 1999 at GL-2340 and
GL-YD, with chlorophyll a concentrations ranging from 41 – 43 µg/L. As a reference,
NCDWQ chlorophyll a concentrations of 40 µg/L to be indicative of algal-impaired waters (NCDWQ 1996). Thus, Greenfield Lake proper is impaired by high fecal coliform
counts, algal blooms, and high sediment metals levels (Mallin et al. 1999); its tributary
stations are impaired by high fecal coliform counts and low dissolved oxygen. Table 6.3. Mean and (standard deviation) of water quality parameters in Greenfield Lake sampling stations. Fecal coliforms given as geometric mean, N/P ratio as median.
_____________________________________________________________________
Parameter GL-2340 GL-YD GL-P _____________________________________________________________________ DO (mg/L) 7.0 (1.7) 8.3 (2.8) 8.9 (2.9) Turbidity (NTU) 5.8 (5.5) 11.1 (15.3) 7.8 (10.1)
TSS (mg/L) 4.4 (2.7) 7.3 (8.8) 7.3 (6.9)
Nitrate (mg/L) 0.179 (0.181) 0.153 (0.201) 0.100 (0.084) Ammonium (mg/L) 0.039 (0.030) 0.056 (0.041) 0.123 (0.309) TN (mg/L) 0.706 (0.400) 0.959 (0.907) 1.422 (2.323) Phosphate (mg/L) 0.031 (0.029) 0.036 (0.032) 0.038 (0.030)
TP (mg/L) 0.101 (0.129) 0.110 (0.114) 0.093 (0.077)
N/P molar ratio 13.3 18.2 9.6 Fec. col. (/100 mL) 460 117 279
Chlor. a (µg/L) 7.2 (11.3) 22.7 (36.3) 19.7 (34.8)
____________________________________________________________________
7.0 Hewletts Creek Hewletts Creek was sampled at five tidally-influenced areas (HC-2, HC-3, NB-
GLR, MB-PGR and SB-PGR) and one freshwater runoff collection area draining Pine
Valley Country Club (PVGC-9 - Fig. 7.1). Physical data indicated that turbidity was excessive on some occasions at NB-GLR, but on average remained below the state standard for estuarine water (Table 7.1). There were several incidents of hypoxia in the spring and summer months at the three upper estuarine stations. Nitrate concentrations
were high in the middle branch (MB-PGR) which drains both Pine Valley and the
Wilmington Municipal Golf Courses (Fig. 7.1; Mallin and Wheeler 2000). Both NB-GLR and SB-PGR also periodically receive elevated nutrient loading as well. Median N/P molar ratios demonstrated that both HC-2 and HC-3 should be primarily nitrogen limited, while NB-GLR tends toward potential phosphorus limitation and SB-PGR could be
either. The chlorophyll a data (Table 7.1) showed that Hewletts Creek continues to host
periodic algal blooms, as it has in the past (Mallin et al. 1998a; 1999). Table 7.1. Selected water quality parameters at tidally-influenced stations in Hewletts Creek watershed as mean (standard deviation) / range, August 1999-July 2000.
_____________________________________________________________________
Parameter HC-2 HC-3 NB-GLR MB-PGR SB-PGR _____________________________________________________________________ Salinity 33.5 (3.1) 32.1 (1.8) 9.2 (8.8) 0.2 (0.3) 19.3 (6.9)
(ppt) 24.3-37.0 30.3-34.9 0.8-26.0 0.1-1.0 7.0-33.0
Turbidity 4.9 (2.0) 5.8 (3.0) 12.3 (8.5) 5.0 (6.7) 12.2 (4.6) (NTU) 1.1-7.5 1.6-10.0 5.4-35.3 0.8-25.3 4.3-17.7
DO 7.6 (1.6) 7.4 (1.9) 7.6 (3.7) 6.7 (1.7) 6.7 (2.4)
(mg/L) 5.5-10.9 5.1-10.4 3.5-16.5 4.3-10.1 3.5-11.4 Nitrate 0.007 (0.009) 0.004 (0.002) 0.131 (0.085) 0.311 (0.113) 0.057(0.034) (mg/L) 0.005-0.033 0.001-0.007 0.001-0.258 0.043-0.439 0.001-0.110
Ammonium 0.015 (0.029) 0.005 (0.006) 0.061 (0.051) NA 0.038 (0.039) (mg/L) 0.001-0.077 0.001-0.013 0.001-0.138 0.001-0.116 Phosphate 0.005 (0.003)0.005 (0.002) 0.018 (0.006) 0.026 (0.022) 0.012 (0.004)
(mg/L) 0.001-0.013 0.002-0.008 0.009-0.029 0.007-0.086 0.006-0.020
Mean N/P 10.3 3.1 (6 mo.) 24.3 NA 17.2 Median 3.8 2.7 25.7 17.1
Chlor a 1.4 (0.9) 1.9 (1.3) 13.5 (36.1) 0.7 (0.5) 5.5 (5.5)
(ug/L) 0.6-5.7 0.6-4.4 0.9-127.8 0.1-1.5 1.0-20.2 _____________________________________________________________________ Turbidity was generally low and dissolved oxygen adequate for the waters
draining the golf course (Table 7.2). Phosphate and nitrate were elevated leaving the
course, but nitrate increased even more downstream at MB-PGR (Tables 7.1 and 7.2). Inputs from Municipal Golf Course or suburban sources may have accounted for the increase. Fecal coliform bacteria counts exceeded state standards 42% of the time in
1999-2000 at PVGC-9. An earlier assessment (Mallin and Wheeler 2000) noted higher
fecal coliform counts entering the course from suburban neighborhoods upstream than counts at PVGC-9 leaving the course. The highest monthly count (13,600 CFU/100 mL) occurred in September after Hurricane Floyd. A collaborative effort among Pine Valley Country Club, New Hanover County, Cape Fear Resource Conservation and
Development, the Clean Water Management Trust Fund, the New Hanover County
Tidal Creeks Program, the N.C. State Cooperative Extension Service at North Carolina State University, the City of Wilmington and UNCW is effecting a stream restoration program on the course that is expected to improve downstream water quality in upcoming years.
Table 7.2. Selected water quality parameters at a freshwater station passing through a country club golf course in Hewletts Creek watershed, as mean (standard deviation) / range, fecal coliforms as geometric mean / range, August 1999-July 2000. _____________________________________________________________________
Parameter PVGC-9
_____________________________________________________________________ Turbidity (NTU) 5.1 (4.5) 1.3-17.5
DO (mg/L) 6.7 (1.8) 3.4-10.0 Nitrate (mg/L) 0.278 (0.274)
0.005-0.940
Ammonium (mg/L) 0.052 (0.039) 0.005-0.140
Phosphate (mg/L) 0.033 (0.022)
0.005-0.090 Mean N/P ratio 44.9 Median 18.1
Chlor a (ug/L) 1.3 (1.3) 0.4-4.3 Fecal coliforms (CFU/100 mL) 303
43-13,600
_____________________________________________________________________ 8.0 Howe Creek Water Quality
Howe Creek was sampled for physical parameters, nutrients, and chlorophyll a at five locations during 1999-2000 (HW-M, HW-FP, HW-GC, HW-GP and HW-DT, Fig. 8.1). Howe Creek, as in past years, portrayed a tidal creek with good water quality near
the ICW and poor water quality in the oligohaline to mesohaline regions. Turbidity was
low near the ICW but exceeded North Carolina water quality standards on five of 12 occasions upstream at HW-DT and on two occasions at HW-GP (Table 8.1; Appendix B). The upper Howe Creek watershed maintains several land clearing and construction projects that appear to affect the water quality by non-point source sediment runoff.
Dissolved oxygen concentrations were generally good in Howe Creek except for three
occasions at HW-GP where it fell below the state standard. Nutrient levels are low near the ICW but can be elevated in the creek near Graham Pond and especially farther upstream (Table 8.2). Algal bloom conditions
(chlorophyll a of 40 µg/L or higher) are rare downstream but occurred on four of 12 occasions at HW-DT (Table 8.1). Median inorganic molar N/P ratios are low to medium, indicating that nitrogen is probably the principal limiting nutrient at stations downstream of HW-GP and often at HW-DT, although periodic nitrate loading events will drive the
ratio upward at times in the upper stations (Table 8.2).
Fecal coliform concentrations demonstrate a creek ranging from good microbiological water quality near the ICW to poor quality above HW-GC (Table 8.1; Fig. 8.2; Appendix B). Both geometric mean fecal coliform counts, and the percent of
counts exceeding 43 CFU/100 mL indicate potentially safe shellfishing water at HW-M
and HW-FP, and unsafe waters at HW-GC and upstream. In fact, the upper stations are also of poor quality regarding human contact, as counts at HW-GP exceeded the state standard of 200 CFU/100 mL 33% of the time and counts at HW-DT exceeded the contact standard 67% of the time (Appendix B). The 1999 hurricanes did not noticeably
affect coliform loading in Howe Creek. A comparison of the three available sampling
years (1993-1994; 1996-1997; 1999-2000) shows virtually identical patterns with no evident major changes in fecal coliform concentrations.
Table 8.1. Water quality summary statistics for Howe Creek, August 1999-July 2000, as mean (st. dev.) / range, fecal coliforms as geometric mean (range) / % of counts
exceeding 43 CFU/100 mL.
Salinity Diss. oxygen Turbidity Fecal coliforms Chlor a
(ppt) (mg/L) (NTU) (CFU/100 mL) (µg/L) _____________________________________________________________________ HW-M 30.1 (3.6) 7.2 (1.7) 5.9 (2.1) 4 (1-51) 1.7 (1.7)
21.5-36.0 4.9-10.3 2.9-10.1 8% 0.3-5.7 HW-FP 27.2 (3.6) 7.2 (1.8) 18.3 (28.1) 6 (1-175) 1.4 (1.5) 13.6-36.6 4.9-10.6 3.0-101.7 8% 0.3-5.2
HW-GC 22.0 (5.3) 7.5 (2.0) 16.7 (12.7) 18 (3-1675) 2.0 (1.8) 1.6-32.0 5.1-11.9 3.9-41.5 25% 0.4-5.3 HW-GP 0.2 (0.3) 7.2 (1.0) 6.6 (2.5) 171 (76-2000) 5.9 (7.8) 0.1-1.0 5.9-9.4 4.5 (13.4) 100% 0.6-28.6
HW-DT 0.2 (0.2) 7.0 (1.7) 7.9 (7.1) 367 (97-2000) 23.3 (27.9) 0.1-1.0 4.8-9.9 3.1-28.5 100% 0.7-92.6
Table 8.2. Nutrient concentration summary statistics for Howe Creek, August 1999-July 2000, as mean (st. dev.) / range, N/P ratio as mean / median.
_____________________________________________________________________
Nitrate Ammonium Phosphate Molar N/P ratio (mg/L) (mg/L) (mg/L) _____________________________________________________________________
HW-M 0.006 (0.009) 0.007 (0.014) 0.006 (0.002) 4.8
0.005-0.033 0.001-0.047 0.003-0.010 2.1 HW-FP 0.006 (0.009) 0.013 (0.023) 0.006 (0.002) 6.9 0.001-0.032 0.001-0.072 0.002-0.009 1.6
HW-GC 0.013 (0.022) NA 0.008 (0.003) NA 0.001-0.076 0.004-0.018 HW-GP 0.025 (0.026) 0.018 (0.017) 0.008 (0.004) 11.7
0.001-0.094 0.001-0.056 0.003-0.018 13.3
HW-DT 0.070 (0.056) 0.028 (0.022) 0.013 (0.010) 20.1 0.001-0.158 0.001-0.069 0.005-0.041 24.7 _____________________________________________________________________
9.0 Motts Creek
Mott’s Creek near River Road has been classified by the State of North Carolina as a Natural Heritage Site because of the area’s biological attributes. These include the
pure stand wetland communities, including a well-developed sawgrass community and
unusually large flats dominated by Lilaeopsis chinensis and spider lily, with large cypress in the swamp forest. Thus, it is important that these attributes should be protected from land and water-disturbing activities. UNCW scientists sampled Mott’s Creek at the River Road bridge (Fig. 9.1). A large development is in the early stages of
construction upstream of the sampling site and between Mott’s and Barnard’s Creeks.
Dissolved oxygen concentrations were not problematic in 1999-2000, and there were no algal bloom problems (Table 9.1). Turbidity was periodically a problem, exceeding the state standard of 25 NTU on two of ten occasions. Fecal coliform
contamination was a problem in Mott’s Creek, with the geometric mean of 292 CFU/100
mL well exceeding the state standard of 200 CFU/100 mL, and monthly samples exceeding this standard on six of ten occasions (Appendix B). Thus, this creek already has some water quality problems. Development activities upstream, if not done in an environmentally-sound manner, will only lead to further degradation of both Mott’s and
Barnard’s Creeks.
Table 9.1. Selected water quality parameters at a station (MOT-RR) draining Motts Creek watershed before entering the Cape Fear Estuary, as mean (standard deviation) / range, October 1999-July 2000. Fecal coliforms as geometric mean / range.
_____________________________________________________________________
Parameter MOT-RR _____________________________________________________________________ Salinity (ppt) 2.6 (4.5)
0.1-14.3
TSS (mg/L) 13.8 (8.6) 5.0-32.0
Turbidity (NTU) 20.7 (7.2)
13.0-33.9 DO (mg/L) 7.0 (2.2) 3.2-10.6
Nitrate (mg/L) 0.167 (0.139) 0.050-0.450 Ammonium (mg/L) 0.062 (0.049)
0.005-0.170
Total nitrogen (mg/L) 0.615 (0.304) 0.200-1.210
Phosphate (mg/L) 0.050 (0.020)
0.020-0.080 Total phosphorus (mg/L) 0.081 (0.034) 0.040-0.150
Mean N/P ratio 11.2 Median 8.6
Chlor a (µg/L) 2.7 (1.1)
1.2-3.8 Fecal coliforms (CFU/100 mL) 292 39-2000
_____________________________________________________________________
10.0 Pages Creek Pages Creek was sampled at three stations, two of which receive drainage from
developed areas (PC-BDUS and PC-BDDS) and a well-flushed one near the ICW (PC-
M - Fig. 10.1). There has been recent drainage system modification in the vicinity of PC-BDUS. During the past sample year turbidity was low to moderate with only one incident of turbidity exceeding the state standard of 25 NTU (Table 10.1). However, there were a few incidents of hypoxia during summers of 1999 and 2000, including
three at the station draining lower Bayshore Drive (BC-BDDS). Nutrient concentrations
were normally low, and phytoplankton biomass was low (Table 10.1). Inorganic nitrogen-to-phosphorus molar ratios were below 16, indicating that phytoplankton growth in this creek is probably nitrogen limited. This is one of the least-polluted tidal creeks in New Hanover County (Mallin et al. 1998a; Mallin et al. 2000a).
Table 10.1. Selected water quality parameters in Pages Creek as mean (standard deviation) / range, August 1999-July 2000. _____________________________________________________________________ Parameter PC-M PC-BDDS PC-BDUS
_____________________________________________________________________
Salinity 34.2 (1.3) 24.5 (11.8) 21.2 (7.5) 32.7-36.3 1.4-35.4 1.1-27.9
Turbidity (NTU) 7.1 (3.2) 13.3 (12.2) 10.2 (4.0)
1.5-11.7 3.1-44.4 4.0-15.5 DO (mg/L) 7.0 (1.9) 6.5 (2.6) 5.8 (2.0) 4.5-10.2 1.6-10.3 2.4-8.4
Nitrate (mg/L) 0.006 (0.006) 0.021 (0.017) 0.017 (0.008) 0.001-0.025) 0.004-0.065 0.005-0.030 Ammonium (mg/L) 0.014 (0.015) 0.022 (0.018) 0.041 (0.028)
0.001-0.035 0.001-0.053 0.001-0.053
Phosphate (mg/L) 0.006 (0.002) 0.010 (0.005) 0.014 (0.005) 0.004-0.009 0.003-0.021 0.004-0.023
Mean N/P Ratio 6.9 10.8 9.4
median 5.4 8.9 10.3
Chlor a (µg/L) 1.3 (0.9) 3.2 (2.8) 4.4 (4.0)
0.3-3.3 0.3-7.8 0.4-13.0
_____________________________________________________________________
11.0 Smith Creek Sampling of Station SC-GT, a tributary of Smith Creek draining a highway
construction area (Smith Creek Parkway) was ceased this year following completion of
that area of the Smith Creek Parkway. Two estuarine sites on Smith Creek proper, SC-23 and SC-CH (Fig. 11.1) were sampled. Dissolved oxygen concentrations were below 5.0 ppm on four of 12 occasions at SC-CH and four of 12 occasions at SC-23. Thus, low dissolved oxygen continued to be a water quality problem in Smith Creek. The
North Carolina turbidity standard for estuarine waters (25 NTU) was exceeded on two of
12 occasions at SC-CH and only one of 12 occasions at SC-23. Both Smith Creek stations had overall mean turbidities below the standard (Table 11.1). One reason for the decrease in turbidity and suspended solids concentrations in Smith Creek was the cessation of construction activities and subsequent opening of the Smith Creek
Parkway to traffic. Also, a ditched wetland area along the Smith Creek Parkway was
naturally revegetating, retarding runoff-driven sedimentation into the creek. On average, most nutrient concentrations were unremarkable, with no defined spatial pattern (Table 11.1). Fecal coliform bacteria levels exceeded the North Carolina
standard for human contact waters (200 CFU/100 mL) four times at SC-23 and three
times at SC-CH during the twelve sample trips; thus, fecal coliform pollution is a problem in Smith Creek (Appendix B). The geometric mean fecal coliform concentration was below the human contact standard at both stations but well above the shellfishing standard (14 CFU/100 mL) in the estuarine portion of the creek (Table 11.1). The
highest monthly counts occurred in September 1999, following Hurricane Floyd. Station
SC-23 yielded 2,500 CFU/100 mL and SC-CH 240 CFU/100 mL. October’s counts may have been affected by Hurricane Irene with counts of 450 CFU/100 mL at both sites. However, in November high counts also occurred with 800 CFU/1000 ml at SC-23 and 400 CFU/100 mL at SC-CH. Smith Creek has been targeted for restoration by the
North Carolina Wetlands Restoration Program.
Table 11.1. Selected water quality parameters in Smith Creek watershed as mean (standard deviation) / range. August 1999-July 2000. _____________________________________________________________________
Parameter SC-23 SC-CH
_____________________________________________________________________ Salinity (ppt) 0.5 (0.7) 1.5 (2.5) 0.1-2.1 0.1-6.7
Dissolved oxygen (mg/L) 6.4 (2.0) 6.8 (2.4) 2.9-8.8 3.1-9.9 Turbidity (NTU) 16.6 (8.2) 17.1 (6.6)
7.0-34.9 9.0-28.0
TSS (mg/L) 11.0 (5.8) 13.4 (5.1) 1.0-21.0 6.0-16.0
Nitrate (mg/L) 0.056 (0.073) 0.143 (0.181)
0.05-0.260.1 0.005-0.560 Total nitrogen (mg/L) 0.610 (0.333) 0.583 (0.409) 0.140-1.310 0.025-1.130
Ammonium (mg/L) 0.052 (0.031) 0.048 (0.032) 0.005-0.110 0.005-0.100 Phosphate (mg/L) 0.038 (0.019) 0.058 (0.036)
0.10-0.80 0.010-0.120
Total phosphorus (mg/L) 0.108 (0.113) 0.109 (0.030) 0.050-0.460 0.070-0.160
Chlor. a (µg/L) 4.3 (5.2) 1.8 (1.8) 0.3-15.1 0.3-5.5 Fecal col. /100 mL 196 116
(geomean / range) 48-450 23-4000
_____________________________________________________________________
12.0 Upper and Lower Cape Fear Within the Wilmington City limits drainage directly to the Cape Fear River (CFR)
was sampled at one location each in the Upper and Lower Cape Fear Watersheds. The
stream draining the Upper CFR was sampled behind the Wilmington Police Station between 2nd and 3rd Streets (Fig. 12.1). Concentrations of most physical, chemical and biological constituents were low to moderate except for nitrate (Table 12.1), which was elevated at times. We note that overall nitrate decreased from 1997-98 to 1998-99, and
again from 1998-1999 to 1999-2000. The geometric mean fecal coliform count for UCF
was 486 CFU/100 mL for the past year, an increase from last year’s 259 CFU/ 100 mL and well in excess of the state standard of 200 CFU/100 mL. Drainage from the Lower CFR was sampled from the stream draining Greenfield
Lake (Fig. 12.1). Processing within the lake served to keep concentrations of most
constituents relatively low (Table 12.1). Most parameters were below state water quality standards during the sampling period. However, fecal coliform counts exceeded the state standard 58% of the time sampled, demonstrating again the fecal coliform pollution problem in Greenfield Lake (Appendix B).
Table 12.1. Water quality summary statistics (mean (standard deviation) / range) for Wilmington Upper (UCF) and Lower (LCF) Cape Fear Watersheds, 1999-2000. _____________________________________________________________________
Station DO (mg/L) Turbidity (NTU) TSS (mg/L) Fecal col (CFU/100 mL)
_____________________________________________________________________ UCF 8.2 (0.6) 2.0 (1.9) 2.1 (1.7) 486 7.4-9.4 0.1-6.2 0.5-6.0 49-4000
LCF 7.1 (2.9) 5.8 (5.5) 8.0 (14.0) 184 2.1-10.6 1.2-16.0 0.5-51.0 6-6000 _____________________________________________________________________
Nitrate (mg/L) Ammonium (mg/L) Phosphate (mg/L) Chlor a (µg/L) _____________________________________________________________________ UCF 0.981 (0.872) 0.094 (0.206) 0.031(0.015) 0.3 (0.2)
0.080-3.100 0.005-0.740 0.010-0.050 0.0-0.6
LCF 0.275 (0.673) 0.153 (0.180) 0.041 (0.050) 7.6 (11.3) 0.005-2.400 0.020-0.650 0.005-0.190 1.3-42.7 _____________________________________________________________________
13.0 Whiskey Creek Sampling of Whiskey Creek began in August 1999. Five stations were chosen;
WC-M (at the marina near the creek mouth), WC-AB (off a private dock upstream), WC-
MLR (from the bridge at Masonboro Loop Road), WC-SB (in fresh to oligohaline water along the south branch at Hedgerow Lane), and WC-NB (in fresh to oligohaline water along the north branch at Navajo Trail – Fig. 13.1). Dissolved oxygen concentrations were generally good in Whiskey Creek (Table 13.1). Turbidity was normally within state
standards for tidal waters except for a couple of occasions at Station WC-MLR
(Appendix B). There were no excessive algal blooms during this period; chlorophyll a concentrations were usually low (Table 13.1). Nitrate concentrations were highest upstream at WC-NB, followed by WC-SB (Table 13.2). However, phosphate concentrations were similar among all stations. Phosphate and nitrate at WC-MB were
highest among all creek mouth stations in the tidal creek system.
The most problematic pollution parameter was fecal coliform contamination (Table 13.1; Fig. 13.2). Based on geometric mean fecal coliform counts and the percent of the time that the counts exceeded 43 CFU/100 mL, the whole creek is of poor
microbiological condition for shellfishing (Table 13.1). The north branch station also
exceeded the standard for human contact waters 67% of the time and the south branch station 42% of the time (Appendix B). We also note that the creek mouth station at the marina had geometric mean counts considerably higher than creek mouth stations in both Howe and Futch Creeks (Fig. 13.2). Hurricane Floyd led to the highest monthly
counts, with a creek average of 1,600 CFU/100 mL in September 1999.
Table 13.1. Water quality summary statistics for Whiskey Creek, August 1999-July 2000, as mean (st. dev.) / range, fecal coliforms as geometric mean (range) / % of counts exceeding 43 CFU/100 mL.
Salinity Dissolved oxygen Turbidity Chlor a Fecal col.
(ppt) (mg/L) (NTU) (µg/L) (CFU/100 mL) _____________________________________________________________________ WC-MB 30.1 (3.6) 7.2 (1.7) 5.9 (2.1) 1.9 (1.9) 12 (1-200) 21.5-36.0 4.9-10.3 2.9-10.1 0.4-7.6 25%
WC-AB 27.2 (3.6) 7.2 (1.8) 18.3 (28.1) 2.5 (2.3) 36 (4-1275) 13.6-36.6 4.9-10.6 3.0-101.7 0.4-7.6 33% WC-MLR 22.0 (5.3) 7.5 (2.0) 16.7 (12.7) 4.8 (6.3) 93 (18-2000)
1.6-32.0 5.1-11.9 3.9-41.5 0.6-19.8 75% WC-SB 0.2 (0.3) 7.2 (1.0) 6.6 (2.5) 0.8 (0.6) 179 (25-2000) 0.1-1.0 5.9-9.4 4.5 (13.4) 0.1-1.9 84%
WC-NB 0.2 (0.2) 7.0 (1.7) 7.9 (7.1) 0.8 (0.9) 408 (62-2630) 0.1-1.0 4.8-9.9 3.1-28.5 0.0-2.9 100%
Table 13.2. Nutrient concentration summary statistics for Whiskey Creek, August 1999-July 2000, as mean (st. dev.) / range, N/P ratio as mean / median. _____________________________________________________________________
Nitrate Ammonium Phosphate Molar N/P ratio
(mg/L) (mg/L) (mg/L) _____________________________________________________________________ WC-MB 0.017 (0.018) 0.019 (0.024) 0.011 (0.006) 7.8
0.002-0.061 0.001-0.082 0.005-0.027 5.5
WC-AB 0.022 (0.021) 0.021 (0.024) 0.012 (0.006) 7.7 0.002-0.071 0.001-0.085 0.006-0.030 8.4
WC-MLR 0.027 (0.024) 0.024 (0.018) 0.011 (0.005) 10.8
0.002-0.070 0.003-0.056 0.003-0.024 10.5 WC-SB 0.091 (0.049) 0.082 (0.054) 0.013 (0.025) 171.8 0.048-0.234 0.004-0.208 0.001-0.090 65.3
WC-NB 0.151 (0.086) 0.081 (0.056) 0.010 (0.007) 169.1 0.018-0.246 0.005-0.212 0.001-0.029 59.8 _____________________________________________________________________
The overall geometric mean fecal coliform concentration for Whiskey Creek was
79 CFU/100 mL. Comparing this count to the rest of the New Hanover County Tidal Creeks, only Bradley Creek has a greater overall geometric mean (Mallin et al. 2000a). We used the regression equation that was developed in our earlier four-year (1994-1998) study (Mallin et al. 1998a) to estimate average watershed fecal coliform counts
(FC = 5.4 (% impervious surface coverage) – 29.1). Based on the 20.9% impervious
surface coverage (provided by the New Hanover County Planning Department) for 1997 in Whiskey Creek, the predicted fecal coliform mean for the creek should have been 84 CFU/100 mL. Our actual count (79 CFU/100 mL) was extremely close. This provides validation of the usefulness of our model for tidal creek watersheds.
14.0 Rainfall Effects on Silicate Loading to Tidal Creeks
Lawrence B. Cahoon
Department of Biological Sciences UNC Wilmington Introduction
New Hanover County’s tidal creeks receive freshwater input from local watersheds through two pathways: surface runoff of precipitation and groundwater discharge. The conventional view is that storm water runoff carries elevated levels of nutrients, whereas base flows in streams, driven largely by groundwater discharge into
stream channels, carry very low nutrient concentrations and total loads into the tidal creeks. This view may be largely correct when considering the nutrients nitrogen and phosphorus, but another important nutrient, silicate (SiO3-2), may behave very differently.
Silicate is an important nutrient for many estuarine plants. Benthic and planktonic diatoms, which are important microscopic primary producers in local estuarine waters, have cell walls made of silica derived from uptake of dissolved silicate (Sigmon, 1995). Marsh grasses, including the widely distributed and important species of Spartina, contain a significant amount of silica (Norris and Hackney, 1999). Although several roles
for this silica have been suggested, it is clear that silica is an important constituent of marsh grasses (Hackney et al., 2000). A few estuarine animals also contain significant amounts of silica, including sponges. Dissolved silicate is derived from the chemical weathering of silicate minerals.
Consequently, groundwater tends to have high concentrations of silicate. Silicate is not volatile, so there is little of it in the atmosphere. Consequently, rainfall contains relatively little dissolved silicate. These two sources of surface water therefore represent the ends of a spectrum of silicate concentration.
Urbanization of New Hanover County’s tidal creek watersheds has altered the hydrological cycle by increasing impervious surface, channelizing streams, ditching and draining wetlands, changing the mix of well-water and municipal water usage, changing the mix of central and on-site sewage treatment systems, reducing forested cover of the landscape, etc. These alterations have likely increased the surface runoff of
precipitation while reducing groundwater flows and discharges. Therefore, one possible result of urbanization in New Hanover County’s tidal creek watersheds is to reduce silicate loading to estuarine waters while increasing loadings of nitrogen and phosphorus in stormwater runoff. The resulting change in the ratios of delivery of these major nutrients may alter the composition and health of estuarine plant communities.
This study focused on determining the response of silicate concentration to precipitation events in a stream draining into a local tidal creek.
Methods The study area was located in the Clear Run Branch drainage area of Bradley
Creek (see Fig. 3.1). This tidal creek’s basin is among the most heavily urbanized in
New Hanover County. The basin drains large areas of impervious surface and is extensively developed with a mixture of residential, commercial, and other establishments (Mallin et al., 2000). The basin is served entirely by central sewer, which reduces groundwater recharge from septic tanks.
Rainwater was sampled at 5322 Clear Run Drive (<50 m from Clear Run Branch) using a 6.5 cm plastic funnel in a replaceable 50 ml polypropylene centrifuge tube mounted at an elevation of 2 m. The nearest trees were >5 m away, so only direct precipitation was sampled. Samples were collected and the sample tube replaced after
each rain event or as the tube was filled during heavy rain events. Sample tubes were
labeled and refrigerated after collection. A datalogging digital rain gauge (Onset Applications) was deployed at the same location and downloaded periodically using BoxCar® software. Rainfall data were
expressed as inches per day for the 24 period beginning at 0900. Rainfall data from a
few missing days were obtained from the local National Weather Service, which uses the same daily reporting period. Stream water samples were collected daily or, in the case of major runoff events,
twice daily from Clear Run Branch, a major tributary to Bradley Creek, at the same
address above. Samples were collected manually by dipping a clean, 50 ml polypropylene centrifuge tube into the stream. Sample tubes were labeled and refrigerated after collection.
Dissolved reactive silicate was measured in rainwater and stream water samples
using the molybdenum-blue spectrophotometric method (Parsons et al., 1984). Previous studies established that freezing alters silicate concentrations measured subsequently, so samples were refrigerated in the dark until analysis in approximately monthly batches.
Results This project measured silicate concentrations in rainwater and stream water during a six month period (August 8, 1999 – February 13, 2000) that encompassed
relatively wet/dry and warm/cold periods and included several major rain events, including Hurricanes Dennis, Floyd, and Irene and Tropical Storm Harvey. Silicate concentrations in rainwater were typically very low, averaging 0.8 uM
(std. dev. = 1.8, n=30, range = 0.0 to 9.9 uM; or 22 µg/L + 50 µg/L, range 0-277 µg/L).
Reactive silicate was detected in most rainwater samples, most likely owing to siliceous dust captured in precipitation. Silicate concentrations in water from Clear Run Branch varied in direct response
to rain events (Fig. 14.1). Detectable rain events corresponded with dips in silicate
concentrations. The largest rain events correlated with substantial drops in silicate
concentrations. Flooding associated with Hurricane Floyd, which yielded >17” of rain at the study location over 36 hours (days 77-78), correlated with a decline in silicate
concentration to 0 µM. Silicate concentrations returned to pre-rain event levels usually
within 1-2 days after rain stopped. Silicate concentrations in Clear Run Branch during non-rain periods averaged
approximately 70-80 µM (1960-2240 µg/L). The “background” silicate concentration
during rain-free periods appeared to vary slightly over the sampling time. Silicate
concentrations in the stream during non-rain periods was slightly lower after the large rain events associated with the hurricanes and tropical storm on days 61, 77-78, 90-91, and 108, and appeared to rise several weeks after these large events.
Discussion Low silicate concentrations in rainfall and rapid runoff of precipitation drive large flows of low silicate water through Clear Run Branch during precipitation events. In contrast, base flow in the stream, which is fed by groundwater discharge, flushes much
lower volumes of water with much higher concentrations of silicate downstream. If conditions in Clear Run Branch are similar to those in other streams feeding the tidal creeks in New Hanover County, then a spectrum of silicate loadings and concentrations is expected in response to varying weather conditions. Wet weather
periods may fill tidal creeks with relatively fresh, low silicate water, while dry periods would permit lower flows of fresh water with much higher silicate concentrations to enter. Flow volume calculations are necessary before the total silicate loadings under these two contrasting weather conditions can be compared. These calculations are underway using data from a stream level gauge in Clear Run Branch.
The likely alterations in the hydrology of Bradley Creek’s watershed and others in New Hanover County may also affect silicate loading. Higher storm water runoff volumes and lower groundwater flux rates may act to reduce the net loading of silicate to the estuaries in this region compared to earlier conditions. Human impacts on
hydrology may, therefore, have altered the balance of silicate vs. other macronutrients in these estuarine ecosystems. If so, changes in estuarine communities may result from more subtle human impacts than previously thought.
References Norris, A.R., and C.T. Hackney. 1999. Silica content of a mesohaline marsh in North
Carolina. Estuarine Coastal and Shelf Science 49:595-601.
Hackney, C.T., L.B. Cahoon, C. Preziosi, and A. Norris. 2000. The links between tidal marshes and estuarine fisheries: A new paradigm. Concepts and Controversies in Tidal Marsh Ecology Symposium. (In press).
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.
Parsons, T.R., Y. Maita, and C.M. Lalli. 1984. A manual of chemical and biological
methods for seawater analysis. Pergamon Press, New York. Sigmon, D.E. 1995. The effects of benthic microalgae on sediment nutrient fluxes. Unpublished M.S. Thesis, Dept. of Biological Sciences, UNC Wilmington, 33 pp.
Figure Legend Fig. 14.1. Plot of silicate concentration (top plot, uM reactive dissolved silicate) and daily
rainfall (bottom plot, inches/day) vs. date (Day #1 = July 1, 1999) in Clear Run Branch,
Bradley Creek watershed.
15.0 References Cited APHA. 1995. Standard Methods for the Examination of Water and Wastewater, 19th ed.
American Public Health Association, Washington, D.C.
Hecky, R.E. and P. Kilham. 1988. Nutrient limitation of phytoplankton in freshwater and marine environments: A review of recent evidence on the effects of enrichment. Limnology and Oceanography 33:796-822.
Mallin, M.A., L.B. Cahoon, J.J. Manock, J.F. Merritt, M.H. Posey, R.K. Sizemore, W.D. Webster and T.D. Alphin. 1998a. A Four-Year Environmental Analysis of New
Hanover County Tidal Creeks, 1993-1997. CMSR Report No. 98-01, Center for Marine Science Research, University of North Carolina at Wilmington, Wilmington,
N.C.
Mallin, M.A., L.B. Cahoon, J.J. Manock, J.F. Merritt, M.H. Posey, T.D. Alphin, D.C. Parsons and T.L. Wheeler. 1998b. Environmental Quality of Wilmington and New
Hanover County Watersheds, 1997-1998. CMSR Report 98-03. Center for Marine Science Research, University of North Carolina at Wilmington, Wilmington, N.C.
Mallin, M.A., S.H. Ensign, D.C. Parsons and J.F. Merritt. 1999. Environmental Quality of
Wilmington and New Hanover County Watersheds, 1998-1999. CMSR Report No. 99-02. Center for Marine Science Research, University of North Carolina at Wilmington, Wilmington, N.C.
Mallin, M.A. and T.L. Wheeler. 2000. Nutrient and fecal coliform discharge from coastal North Carolina golf courses. Journal of Environmental Quality 29:979-986. Mallin, M.A., K.E. Williams, E.C. Esham and R.P. Lowe. 2000a. 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. 2000b. Restoration of shellfishing waters in a tidal creek following limited dredging.
Journal of Coastal Research 16:40-47.
NCDEHNR. 1996. Water Quality Progress in North Carolina, 1994-1995 305(b) Report. Report No. 96-03. North Carolina Department of Environment, Health, and Natural Resources, Division of Water Quality. Raleigh, N.C.
Parsons, T.R., Y. Maita and C.M. Lalli. 1984. A Manual of Chemical and Biological Methods for Seawater Analysis. Pergamon Press, Oxford. 173 pp. Schlotzhauer, S.D. and R.C. Littell. 1987. SAS system for elementary statistical
analysis. SAS Institute, Inc., SAS Campus Dr., Cary, N.C.
U.S. EPA. 1997. Methods for the Determination of Chemical Substances in Marine and Estuarine Environmental Matrices, 2nd Ed. EPA/600/R-97/072. National Exposure Research Laboratory, Office of Research and Development, U.S. Environmental
Protection Agency, Cincinnati, Ohio.
Welschmeyer, N.A. 1994. Fluorometric analysis of chlorophyll a in the presence of chlorophyll b and phaeopigments. Limnology and Oceanography 39:1985-1993.
16.0 Acknowledgments Funding for this research was provided by New Hanover County, the Northeast
New Hanover Conservancy, the City of Wilmington and the University of North
Carolina at Wilmington. For project facilitation and helpful information we thank Paul Foster, Dexter Hayes, Matt Hayes, Patrick Lowe, David Mayes, Chris O’Keefe, Rick Shiver and Dave Weaver. For field and laboratory assistance we thank Jesse Cook, Heather CoVan, Matt McIver and Brad Schroeder.
17.0 Appendix A. North Carolina Water Quality standards for selected parameters (NCDEHNR 1996). _____________________________________________________________________
Parameter Standard _____________________________________________________________________ Dissolved oxygen 5.0 ppm (mg/L)
Turbidity 25 NTU (tidal saltwater) 50 NTU (freshwater) Fecal coliform counts 14 CFU/100 mL (shellfishing waters), and more than 10% of
the samples cannot exceed 43 CFU/100 mL.
200 CFU/100 mL (human contact waters)
Chlorophyll a 40 ppb (µg/L)
_____________________________________________________________________
CFU = colony-forming units mg/L = milligrams per liter = parts per million
µg/L = micrograms per liter = parts per billion
18.0 Appendix B. Use support of Class C surface waters in Wilmington and New Hanover County watersheds based on August 1999 – July 2000 data (where available) for chlorophyll a, dissolved oxygen, turbidity, and fecal coliform based on
North Carolina state standards**.
_____________________________________________________________________ FS (fully supporting) – state standard exceeded in < 10% of the measurements PS (partially supporting) – state standard exceeded in 11-25% of the measurements NS (non supporting) – state standard exceeded in >25% of the measurements
_____________________________________________________________________
Watershed Station Chlor a DO Turbidity Fecal coliforms*
Barnard’s Creek BNC-TR FS PS FS NS BNC-CB FS FS FS NS BNC-EF FS PS FS NS
BNC-AW FS NS FS NS
BNC-RR FS PS NS PS Bradley Creek BC-CA FS PS FS NS BC-CR FS FS FS -
BC-SB FS PS FS -
BC-SBU FS PS FS - BC-NB FS PS FS - BC-NBU FS FS FS - BC-76 FS PS FS -
Burnt Mill Creek BMC-AP1 FS PS FS NS BMC-AP2 FS PS FS NS BMC-AP3 FS FS FS NS BMC-PP FS NS FS NS
Futch Creek FC-4 FS PS FS FS FC-6 FS PS FS FS FC-8 FS PS PS FS FC-13 FS PS NS FS
FC-17 FS PS PS FS FOY FS PS PS FS Greenfield Lake GL-SS1 FS PS FS NS GL-SS2 FS FS FS NS
GL-LC FS NS FS NS GL-JRB FS NS FS NS GL-LB FS NS FS NS GL-2340 FS FS FS NS GL-YD PS PS FS NS
GL-P PS FS FS NS
Hewletts Creek PVGC-9 FS PS FS NS MB-PGR FS PS FS - NB-GLR FS PS FS -
SB-PGR FS PS FS -
HC-3 FS FS FS - HC-2 FS FS FS - Howe Creek HW-DT NS PS NS NS
HW-GP FS PS FS NS
HW-GC FS PS FS FS HW-FP FS FS FS FS HW-M FS FS FS FS
Motts Creek MOT-RR FS FS PS NS
Pages Creek PC-BDUS FS PS FS - PC-BDDS FS PS FS - PC-M FS PS FS -
Smith Creek SC-23 FS NS FS NS SC-CH FS NS PS PS Upper and Lower UCF-PS FS FS FS NS
Cape Fear LCF-GO FS PS FS NS
Whiskey Creek WC-NB FS PS FS NS WC-SB FS FS FS NS WC-MLR FS FS PS PS
WC-AB FS FS FS FS
WC-MB FS FS FS FS _____________________________________________________________________ * fecal coliform category used here is based on the human contact standard of 200 CFU/100 mL, not the shellfishing standard of 14 CFU/100 mL.
** NCDWQ only lists fecal coliform contaminated waters as NS if five samples are
collected in a 30-day period and standard is exceeded > 25% of the time; thus, this appendix should be considered a guide for polluted waters rather than a legal standard.
19.0 Appendix C. University of North Carolina at Wilmington reports and papers concerning water quality in New Hanover County’s tidal creeks.
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., E.C. Esham, K.E. Williams and J.E. Nearhoof. 1999. Tidal stage variability
of fecal coliform and chlorophyll a concentrations in coastal creeks. Marine Pollution
Bulletin 38:414-422. Mallin, M.A. and T.L. Wheeler. 2000. Nutrient and fecal coliform discharge from coastal North Carolina golf courses. Journal of Environmental Quality 29:979-986.
Mallin, M.A., K.E. Williams, E.C. Esham and R.P. Lowe. 2000. Effect of human development on bacteriological water quality in coastal watersheds. Ecological
Applications 10:1047-1056.
Mallin, M.A., L.B. Cahoon, R.P. Lowe, J.F. Merritt, R.K. Sizemore and K.E. Williams.
2000. Restoration of shellfishing waters in a tidal creek following limited dredging.
Journal of Coastal Research 16:40-47.
Mallin, M.A., 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.
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.