Assessment of stream quality using biological indices at selected sites in the Delaware River basin, Chester County, Pennsylvania, 1981-97

Abstract

Introduction In 1970, the Chester County Water Resources Authority (Penn-sylvania) and the U.S. Geological Survey (USGS) established a long-term water-quality network with the goal of assessing the quality of streams in the county and understanding stream changes in response to urbanization using benthic-macroinvertebrate data. This database represents one of the longest continuous water-quality data sets in the country. Benthic macroinvertebrates are aquatic insects, such as mayflies, caddisflies, riffle beetles, and midges, and other invertebrates that live on the stream bottom. Benthic macroinvertebrates are useful in evaluating stream quality because their habitat preferences and low motility cause them to be affected directly by substances that enter the aquatic system. By evaluating the diversity and community structure of benthic-macroinvertebrate populations, a determination of stream quality can be made. Between 1981 and 1997, the water-quality network consisted of 43 sites in 5 major basins in Chester County—Delaware, Schuylkill, Brandywine, Big Elk and Octoraro, and Red and White Clay. Benthic-macroinvertebrate, water-chemistry, and habitat data were collected each year in October or November during base-flow condition. Using these data, Reif evaluates the overall water-quality condition of Chester County streams. This Fact Sheet summarizes the key findings from Reif for streams in the Delaware River Basin. These streams include Darby Creek (site 17), Crum Creek (site 19), Ridley Creek (sites 20 and 21), East Branch Chester Creek (sites 22-24, and 51), and Goose Creek (site 25). This summary includes an analysis of stream conditions on the basis of benthic-macroinvertebrate samples and an analysis of trends in stream conditions for the 17-year study period.