Biological Impacts of Urbanization in Valley Creek, PA

Dr. Susan Kilham
Department of Biosciences
Drexel University
kilhams@drexel.edu

General results:
        * There is decreasing fish diversity with increasing impervious surface cover, but this is ameliorated to some degree by areas of groundwater influx.
        * Fish communities are very patchy in Valley Creek, with adjacent stations having an average of 50% similarity.
        * From 1993 to 2001/2002, percent similarity of fish communities was only 68% for the watershed, and 50% for Little Valley Creek.
        * Since 1993, brown trout have declined in abundance and distribution in Valley Creek, from 25% to 12% of total fish abundance.
        * Brown trout have very limited ranges of movement in the stream.    
        * Increased stream temperature from urban runoff is of increasing concern, especially for trout, with summer temperatures reaching the low end of the lethal range.
        * Increasing fine particulate matter from urbanization degrades habitat for many organisms.
        * Stable nitrogen isotope analyses revealed an elevated d¹⁵N at all food web levels at stations downstream of the septic/sewer divide in the Valley Creek Branch. This is a useful management tool for evaluating human sewage inputs in urban areas.
        * PCBs are biomagnified in the food web in Little Valley Creek.

Valley Creek watershed is no longer in "an excellent state of health" and conditions will likely worsen as urbanization continues. It is in jeopardy of losing its "Exceptional Value" status based on the decline of the brown trout. Strong efforts should be made to control stormwater run-off, restore riparian areas, and protect springs.

Print page                                                                                                              Last updated: 09/03/2004