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Preliminary Results from a Study of the Impact of Walker Lake on the North Branch of Middle Creek Using Metrics Generated by Diatom Biofilm Communities

Shannon Ryan and Jack Holt, Jack Holt, Department of Biology, Susquehanna University, 514 University Avenue, Selinsgrove, PA 17870

      Middle Creek is a tributary of the main stem of the Susquehanna River, and its watershed is confined mostly to Snyder County. The upper reaches of the stream are defined by two major branches, the North Branch and the West Branch, each of which is interrupted by a reservoir, Walker Lake and Faylor Lake, respectively.  Walker Lake is an impoundment of a deep V-shaped valley and is 9-10 meters deep at the dam, which allows it to be stratified in the summer and winter.  During September of 2019 and 2020, the hypolimnion of Walker Lake became anoxic and its outflow below the dam had a strong odor of hydrogen sulfide and deposits of iron (III) oxide-hydroxide covered the cobbles and small boulders.  The purpose of this preliminary investigation is to explore the impact of the bottom outflow below the dam and at sample sites before and after fall turnover and use them as proxies for the state of the stream.  We examined four sites on the North Branch: above the lake, Walker Lake, below the dam at its outflow, and a site downstream called Old Bridge. Field measurements with a YSI 556 multimeter were taken. The loss of alkalinity and conductivity were particularly noticeable.  The alkalinity decreased by 35% between the above site and below the dam. Before turnover, at the below site, biofilm diatoms were scarcely found such the phytoplankter, Asterionella formosa, was the most abundant diatom species encountered from the stones collected.  Following turnover, the biofilm community was dominated by Achnanthidium minutissumum in November 2019. Preliminary metrics based on diatom community analysis before and after turnover suggest the above lake site was impaired by agriculture, but the reservoir didn't function as a sediment or nutrient trap.  The downstream sites showed higher impairment than the above lake site. 




Additional Abstract Information

Presenter: Shannon Ryan

Institution: Susquehanna University

Type: Poster

Subject: Ecology

Status: Approved


Time and Location

Session: Poster 5
Date/Time: Tue 12:30pm-1:30pm
Session Number: 4101