PRELIMINARY HYDROGEOCHEMICAL BUDGETS FOR SENECA LAKE, NY

Seneca Lake, located in central New York State, is the largest (15.5 km³) and deepest (186 m) of the 11 Finger Lakes. It is an ideal natural laboratory for hydrogeochemical studies because individual subwatersheds contain different land use, bedrock and physiographic characteristics. Weekly samples from the non winter months were used to construct a preliminary hydrogeochemical budget for the major ions. Over the past three years, samples were collected from four lake sites and less frequently from up to eighteen streams within the Seneca Lake watershed. They were measured for Cl, Na, SO₄, K, Ca and Mg, using an ion chromatograph, and other limnological parameters following standard techniques. The major ion concentrations in the lake are constant over time and location, suggesting that the ions are probably at equilibrium.

Stream ion concentrations, however, change slightly over time, between streams, and between the streams and the lake. Ion concentrations in each stream typically increase in summer, and relate to minimal stream discharge. Between streams, calcium, magnesium, and sulfate concentrations are higher in streams underlain by limestone than those underlain by shale. This association will be the focus of future research that will determine the mineral composition of the bedrock by XRD.

Comparisons between the lake and stream data reveal three ion groups. Chloride, sodium, and sulfate concentrations are larger in the lake than the streams, especially for chloride and sodium. This trend is consistent with groundwater inputs that leach Silurian evaporites below the lake floor as hypothesized for chloride by earlier researchers. Conversely, calcium and magnesium concentrations are smaller in the lake than the streams. Both ions are probably removed from the lake by zebra and quagga mussel shell formation and inorganic precipitation of calcite during summer whiting events. Potassium concentrations are essentially the same between the lake and streams which suggest no extra sources or sinks.