WATER QUALITY MONITORING TO ASSESS THE EFFECT OF NON-POINT SOURCE NUTRIENT AND OTHER POLLUTANT LOADS ON AN ESTUARINE WATERSHED

This study directly assesses the suburbanization impact of a major golf course/housing development on an estuarine watershed. Within the regional Delaware Bay watershed, three sites located in New Castle County, Delaware were selected for sampling: Beaver Branch and Hangman’s Run, both adjacent to the development site and Blackbird Creek, a control site.

Water quality monitoring includes the collection of field measurements and samples for laboratory analyses at two-week intervals. Additionally, a series of storm-event field and laboratory measurements are collected at the sampling sites. Field analyses include monitoring of: temperature, specific conductivity, salinity, dissolved oxygen, depth, pH, and turbidity. Laboratory analyses include concentration measurements of: dissolved and particulate forms of ammonium nitrogen, nitrate nitrogen, total Kjeldal nitrogen, orthophosphate, total phosphates, chemical oxygen demand, and solids. Additionally chlorophyll, pheophytin, and silicate are determined. Seasonal variability of nutrient utilization are determined for Beaver Branch and Hangman’s Run and compared to those at Blackbird Creek. Data are used to determine the extent to which nutrients accumulate in the water column and how the integrated nutrients in the study area respond to the loadings. Time series water quality data are analyzed on various time scales (from daily for storm discharges, to seasonal and annual for the biweekly sampling) for computation of nutrient loadings.

Preliminary results from 1.5 years of data collection reveal that nutrient concentrations are dependent on base flow discharge. As an example, biweekly grab sample levels of nutrients are generally lower during drought. In addition, nutrient concentrations in storm samples are dependent on the rate and duration of rainfall, as well as the spatial aspect of the tide cycle. As expected, Hangman’s Run has elevated nutrient levels compared to Beaver Branch and Blackbird Creek because of its relative restriction to tidal flow. Both Beaver Branch and Blackbird Creek demonstrate higher levels of nutrients in winter and spring. Spring levels may be associated with production and winter levels may be attributed to a reservoir effect.