Since 1969, the U.S. Geological Survey and the Chester County Water Resources Authority have conducted a cooperative program to evaluate stream ecology and water-quality conditions using benthic macroinvertebrates and stream-water chemistry. The Stream Conditions of Chester County Program has sampled streams every fall for over 30 years. The initial goals of the program were to evaluate stream-water quality and to further the understanding of changes in the stream ecosystem in response to urbanization. The current goals of the program are to use the data to monitor current conditions and determine trends. Data from the program have been used to help support Chester County Landscapes by providing information on biological diversity and water-quality conditions. Without monitoring it is impossible to determine if changes in land use or environmental policies and regulation are having a positive affect on water quality.
Benthic macroinvertebrates are macroscopic animals that inhabit the bottoms of aquatic habitats. Freshwater forms include aquatic insects and other invertebrates including clams, crustaceans, snails, and worms. Factors such as streamflow, food availability, habitat, temperature, and water quality determine the makeup of the macroinvertebrate community. By sampling in similar habitats with similar physical conditions, water quality becomes the determining factor controlling community structure. Changes in abundance, diversity, species richness, and presence or absence of pollution tolerant or intolerant species can be measured and related to water quality. Trends in water quality can be determined by sampling at a single location over several years and observing changes to the community structure.
Benthic macroinvertebrates are well suited as water-quality indicators because of their biology and availability. They are present in most aquatic systems and are relatively easy to collect. They are indicators of overall water quality and can be used to identify specific types and sources of degraded water quality. Benthic macroinvertebrates have limited mobility and cannot avoid poor water-quality conditions. They are sensitive to a wide range of environmental impacts including chemical and physical impairments.
Biological samples collected for the Stream Conditions of Chester County Biological Monitoring Network consist of benthic macroinvertebrates collected from a riffle area of the stream. A riffle habitat is used because macroinvertebrate diversity and abundance is usually highest there.
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Sample collection and identification methods remained consistent from 1970 through 1997. Benthic macroinvertebrates were collected by taking 10 rocks (45-90 millimeters in diameter) at random. Water-quality conditions were determined by analysis of the community structure and calculation of Brillouin's Diversity Index. In this index, diversity is high if a community contains many organisms that are evenly distributed; diversity is low if there are few organisms that are unevenly distributed. Brillouin's diversity index values greater than 3.0 are associated with waters receiving little or no organic wastes. Values between 1.0 and 3.0 are associated with waters receiving moderate organic wastes, and values below 1.0 are associated with waters receiving heavy organic wastes.
A new sampling protocol for the Stream Conditions of Chester County Biological Monitoring Network was established in 1998 to update the program and meet the county's current needs. The new sampling protocols are based on Rapid Bioassessment Protocols (RBP) established by the U.S. Environmental Protection Agency. Samples are collected from areas of various velocities from within a riffle. Water-quality conditions are determined by analysis of the community structure and calculation of various metrics including total individuals, taxa richness, Brillouin's Diversity Index, Hilsonhoff Biotic Index, EPT taxa richness, percent EPT taxa, and percent dominate taxa. This sampling method will allow the county to compare results with those from the Pennsylvania Department of Environmental Protection, universities, local watershed associations, and other federal agencies that are using RBP's.
Sampling locations were adjusted in 1998 to relocate the sampling sites to better meet the county's needs. Twenty-seven sites are samples each year. Eighteen sites are fixed integrator or reference sites. These fixed integrator sites are sampled every year. Nine sites are selected each year to assess the water quality in areas of interest to the county. The realignment of sampling sites provides better spatial coverage while increasing flexibility. The increased flexibility allows for the placement of sites to study the effects on water-quality of specific events such as road construction or residential and business developments. This makes the program capable of both short-term and long-term evaluation of stream-water quality.
The Stream Conditions of Chester County Program has determined that the quality of Chester County streams has greatly improved since 1970. Current benthic macroinvertebrate communities are more diverse and contain more pollution sensitive species compared to communities sampled at the beginning of the program. Forty-five of forty-six sites analyzed between 1970 and 1986 had a statistically significant increase in diversity.
macroinvertebrate indices, stream chemistry, pennsylvania, christina river, brandywine creek,
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Citation for This Dataset
USGS, Chester County Water Resources Authority, [year], accessed [date], at URL [http://pa.water.usgs.gov/projects/assessments/chesco/bio_chemical.php]
Citation for This Webpage
USGS; Chester County Water Resources Authority (2013). "CZO Dataset: Chester County, PA - Stream Water Chemistry, Stream Ecology (1998-2013) - USGS." Retrieved 19 Feb 2019, from http://criticalzone.org/national/data/dataset/2515/
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