Assessment of stream conditions and trends in biological and water-chemistry data from selected streams in Chester County, Pennsylvania, 1981-97

Biological, chemical, and physical data were collected from a network of 43 sites in Chester County,
Pa., from 1981 to 1997. The goal of the network is to assess stream conditions and determine trends in
benthic-macroinvertebrate and water-chemistry data. Most sites in the network were assessed as
nonimpacted or slightly impacted on the basis of biological metric analysis of benthic-macroinvertebrate
data. Sites assessed as impacted were affected by habitat degradation, organic pollution, or toxins.
Analysis of calculated biological metrics indicates that most sites were assessed as nonimpacted or slightly
impacted between 1981 and 1997. Sites in the Pigeon, French, Pickering, and upper East Branch
Brandywine Creek Basins generally were assessed as nonimpacted with stable physical and chemical data
through the 17-year period. Sites in the Darby, Crum, Ridley, Valley, and lower East Branch Brandywine
Creek Basins are being degraded from the reference conditions, primarily because of habitat alteration.
The areas with the poorest stream quality were sites with greater than 50 percent agricultural land use,
sites with greater than 10 percent impervious surface, and sites affected by wastewater-treatment plant
discharges. These sites are being degraded by erosion, sedimentation, and nutrient enrichment. Trend
analysis indicates that calculated biological metrics at most sites improved or remained unchanged
between 1981 and 1997. Trend analysis on chemical constituents indicated that concentrations of nitrate
and chloride were increasing, and concentrations of phosphorus and ammonia were unchanged or
declining across Chester County from 1981 to 1997. The highest concentrations of ammonia and chloride
were at locations affected by wastewater-treatment plant discharges. Concentrations of pesticides and
other organic compounds in stream-bottom sediments decreased between 1983 and 1997 but these
compounds still are present at low concentrations throughout Chester County.