Sample Collection and Processing
Macroinvertebrate sampling occurred at 18 sites located throughout the White Clay Creek watershed. For most sites, sampling occurred annually from 1991 to 2008 in March or April (no samples were taken in 2002, 2006, or 2007).
Samples were taken in riffle habitat using a Surber sampler (250-µm mesh, 0.093m2). This is a quantitative method of determining the numbers and kinds of macroinvertebrates found on the stream bottom. To dislodge attached organisms rocks within the sampler were scrubbed using a brush and sediments were disturbed. Four samples were taken at each location, except in 1991 and 1992 when two samples were taken. Samples were rinsed through a 1-mm mesh sieve, transferred to a labeled jar, and preserved with 95% ethanol.
Eight sites on the East Branch in the Avondale area were sampled in October 2005 by Avondale High School student, Dylan Kee, under the direction of Stroud Water Research Center. Data was collected and processed in comparable way to other Stream Watch data with the exception of two composite samples instead of four individual samples. In addition, Trout Run (Site 25), a tributary that joins the East Branch in Avondale, was sampled a single time in March 2005.
In the laboratory, a microscope was used to remove ≥200 organisms from detritus material and these individuals were identified usually to family (except in 1991-1993 when many taxa were identified to order), counted, and recorded. In years when samples contained many individuals, only a portion of each sample (e.g., 50%) was processed. Sampling procedures were designed and described in a matter that volunteers with minimal training could collect and process the samples. These protocols are available by contacting the education department at Stroud Water Research Center.
Water chemistry was examined in 1994-1997, 2003-2005, and 2008 (i.e., 8 of the 15 years). Nitrate, ammonium, and soluble reactive phosphorus were measured in all 8 years, but other variables were sampled less often.
|Year||Nitrate||Ammonium||Total Phosphorus||SRP||Sulfate||Alkalinity||pH||Conductivity||Dissolved Organic Carbon|
Sampling sites were located with a handheld Garmin 60CS GPS unit and geographic data was mapped with ArcMap (version 9, Environmental Systems Research Institute, Redlands, CA). Watershed boundaries were obtained from the Delaware Valley Regional Planning Commission and a Delaware topoquad obtained from U.S. Geological Survey. Some additional digitizing was done using 7.5 minute digital topoquads. Data layers (land use/cover, imperviousness, and canopy cover) were obtained from the 2001 National Land Cover Data at a resolution of 30-m. Population data (1990 and 2000 Census data) were obtained from the National Historic Geographic Information System. Data layer of PA DEP impaired sites was obtained from www.pasda.psu.edu (accessed 28 Sept 2010).