1.1 Methods           

            Field parameters were measured at each site using a YSI 6920 Multiparameter Water Quality Probe (sonde) linked to a YSI 610 display unit.  Individual probes within the instruments measured water temperature, pH, dissolved oxygen, turbidity, salinity, and conductivity.  YSI Model 85 and 55 dissolved oxygen meters were also used on occasion.  The instruments were calibrated prior to each sampling trip to ensure accurate measurements.

            For the six tidal creeks, water samples were collected monthly, at or near high tide.  For nitrate+nitrite (hereafter referred to as nitrate) and orthophosphate assessment, three replicate acid-washed 125 mL bottles were placed ca. 10 cm below the surface, filled, capped, and stored on ice until processing.  In the laboratory the triplicate samples were filtered simultaneously through 25 mm Millipore AP40 glass fiber filters (nominal pore size 1.0 micrometer) using a manifold with three funnels.  The pooled filtrate was stored frozen until analysis.  Nitrate+nitrite and orthophosphate were analyzed using a Technicon AutoAnalyzer following EPA protocols.  Samples for ammonium were collected in duplicate, field-preserved with phenol, stored on ice, and analyzed in the laboratory according to the methods of Parsons et al. (1984).  Fecal coliform samples were collected by filling pre-autoclaved containers ca. 10 cm below the surface, facing into the stream.  Samples were stored on ice until processing (< 6 hr).  Fecal coliform concentrations were determined using a membrane filtration (mFC) method (APHA 1995).  North Carolina water quality standards relevant to this report are listed in Appendix A.

            The analytical method used to measure chlorophyll a is described in Welschmeyer (1994) and US EPA (1997).  Chlorophyll a concentrations were determined from the 1.0 micrometer glass fiber filters used for filtering samples for nitrate+nitrite and orthophosphate analyses.  All filters were wrapped individually in aluminum foil, placed in an airtight container and stored in a freezer.   During the analytical process, the glass filters were separately immersed in 10 ml of a 90% acetone solution.  The acetone was allowed to extract the chlorophyll from the material for two hours, after which the material was centrifuged, leaving the solution containing the extracted chlorophyll.  Each solution was then analyzed for chlorophyll a concentration using a Turner AU-10 fluorometer.  This method uses an optimal combination of excitation and emission bandwidths that reduces the errors inherent in the acidification technique.

            Samples were collected monthly within the Wilmington City watersheds from August 2002 through September 2003.  Field measurements were taken as indicated above.  Nutrients (nitrate, ammonium, total Kjeldahl nitrogen (TKN), total nitrogen (TN), orthophosphate, and total phosphorus (TP)) and total suspended solids (TSS) were analyzed by a state-certified contract laboratory using EPA and APHA techniques.  We also computed inorganic nitrogen to phosphorus molar ratios for relevant sites (N/P).  Chlorophyll a was run at UNCW-CMS as described above, except filters were ground using a teflon grinder prior to extraction.

            For two wet detention ponds (Ann McCrary Pond on Burnt Mill Creek and Silver Stream Pond in the Greenfield Lake watershed) we were able to obtain data from input (control) and outfall stations.  We used these data to test for statistically significant differences in pollutant concentrations between pond input and output stations.  The data were first tested for normality using the Shapiro-Wilk test.  Normally distributed data parameters were tested using the paired-difference t-test, and non-normally distributed data parameters were tested using the Wilcoxon Signed Rank test.  Statistical analyses were conducted using SAS (Schlotzhauer and Littell 1987).