DIATOMS AS WATER QUALITY INDICATORS IN THE HEADWATERS OF FISHING CREEK (COLUMBIA AND SULLIVAN COUNTIES), PENNSYLVANIA

The headwaters of Fishing Creek in central Pennsylvania are a major source of fresh drinking water for downstream communities, they are also a site of historically high water acidity, attributed to atmospheric deposition (acid rain), breakdown of dissolved organic carbon, and the low buffering capacity of local geology. This situation led to a 2007 action plan to provide liming to the area to maintain a pH suitable for fish. The purpose of the present study was to use a combination of in-situ measurements and the presence or absence of algal diatoms (Class Bacillariophyceae) to assess the effectiveness of said action plan after 10 years.

In-situ data on pH, temperature, conductivity and dissolved oxygen were collected from 8 sample sites in the Fishing Creek watershed: four from the East Branch (EBFC) and four from the West Branch (WBFC). Large volume water samples were also collected for alkalinity and acidity analysis and diatoms collected from each sample site using a rock-scrape technique. Among study sites pH ranged from 4.77 – 7.37, water temperature from 13.7 – 15.2 °C, conductivity from 20.9 – 50.0 µS/cm, and dissolved oxygen from 6.00 – 9.54 mg/L. Alkalinity was low at all sites, ranging from 0 – 5.6 mg/L as CaCO3: acidity ranged from 2.7 – 5.6 mg/L as CaCO₃. Forty-one different diatom genera were observed, the most prevalent of which were Eunotia spp.

A diverse range of diatom species at one headwater stream suggest that treatments to the headwaters of Fishing Creek were beneficial to at least that stream. Low alkalinity and moderate acidity as well as high abundance of acid resistant diatom species indicate acidic conditions may be still problematic to fish in several other headwater streams. Some degree of naturally low pH resulting from dissolved organic carbon breakdown rather than acid deposition was indicated in at least one stream based on the diatom assemblage.