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Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, 2002
in Food Webs
COMMUNITY STRUCTURE OF BIOTA IN AN URBANIZED WATERSHED IN THE PHILADELPHIA AREA.
L.Y. Steffy and S.S. Kilham. School of Environmental Science, Engineering and Policy, Drexel University, Philadelphia, PA 19104
Valley Creek is an urbanized watershed near Philadelphia, PA, and a designated Pennsylvania Exceptional Value stream. Urbanization is most pronounced in the headwaters and decreases downstream toward Valley Forge National Historic Park before the stream enters the Schuylkill River. Valley Creek has two main stems and the watershed is 64 sq. km. in area. It is spring fed in a fractured karstic basin. The watershed has an historical record spanning 300 years, being primarily agricultural in the early years and now having 17% impervious surface and numerous identified toxic waste sites. Fifteen stations were sampled on a seasonal basis (Fall 2000 to present) both upstream and downstream of identified contaminant sources. Stable isotopes were used to identify position in the food web and C:N:P ratios were also determined. Community structure was complex and related to land use. For example, nitrogen isotope signatures were generally elevated in all parts of the food web in the whole system and particularly elevated near housing developments in the Valley Creek branch. C:N ratios in the food web were generally more elevated in Valley Creek than in Little Valley Creek.
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