Water quality monitoring to assess the effect of non-point source nutrient and other pollutant loads on estuarine waters, southern New Castle County, Delaware tributaries of the Delaware Bay
Date
2010
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University of Delaware
Abstract
This study established water quality monitoring baseline values for the discharge of nutrient and non-pollutant loads from two drainage basins prior to suburban housing with golf course development. The drainage basins studied were the Beaver Branch and Hangman’s Run in southern New Castle County, Delaware. Beaver Branch drains directly into the upper portion of the Blackbird Creek, the principal waterway within one component of Delaware’s National Estuarine Research Reserve. Water quality monitoring included the collection of field measurements and samples for laboratory analyses at two-week intervals for the duration of this two-year project. In addition, a series (~2-3 per season) of storm-event, field, and biweekly laboratory measurements were collected at the sampling sites. Field measurements included specific conductivity, temperature, pH, depth, turbidity, salinity, and dissolved oxygen. Laboratory measurements of total dissolved and suspended solids, chlorophyll a, b, and c, pheophytin a, silicate, and dissolved and particulate constituents of ammonium-nitrogen, nitrate-nitrogen, total Kjeldahl nitrogen, orthophosphate, total phosphates, total dissolved phosphorus, and chemical oxygen demand. These data were collected to analyze the loading rates of nitrate species, phosphorus species, silicate, and total solids on streams at the three sites. Stream flow data from the USGS gauge station on Blackbird Creek was used to model flow in the creeks without gauges. This study examined the data on various time scales: annual, seasonal, and storm events. Annual data showed loading rates attributable to local meteorological events on a large temporal scale. The stream flow data (observed and modeled) shows higher loading rates associated with high rates of precipitation. Annual loading rates of nitrogen species vary with rates of precipitation, plant production and decay of plant material. Phosphate species loading rates are associated with amounts of total suspended and dissolved solids. Silicate loading rates are linked to groundwater discharge to streams and precipitation. Similar to annual results, seasonal loading data for nitrogen species reflects the nitrogen cycle (oxidation / reduction). Phosphates are associated with suspended and dissolved solids and silicates follow groundwater discharge. The seasonal data follows climate. Storm events show signals that were not observed in the longer time-scale seasonal and annual data. For example, silicate loads were higher during the July 2003 storm than the October 2002 storm event. The storm data also showed an increased load for nitrogen species during periods of intense rain and after a prolonged steady rain. Storm events also show increased phosphate loads. This study has shown that variability in loading rates of small systems occur on a scale of hours to days. A signal that could not be detected if longer temporal measuring scales were used. This result has implications for the timing intervals of measurements in future studies aimed at measuring changes in loading rates within smaller tidal systems.
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Keywords
Estuarine Waters