A PRELIMINARY CALCIUM BUDGET FOR SENECA LAKE, NEW YORK: FLUVIAL INPUTS AND PROBABLE REMOVAL MECHANISMS

Various carbonate proxies preserved in the sediments of Seneca Lake, NY, have revealed a recently tapped record of Holocene climate change. On shorter timeframes, its hydrogeochemistry has significantly altered since the introduction of zebra mussels (D. polymorpha) in 1992 and quagga mussels (D. bugensis) in 1999. Fundamental to both is calcium. Fluvial input and output data is presented to initiate a preliminary calcium budget for the lake.

Seneca Lake, with a volume of 15.5 km³, and maximum depth of 186 m, is the largest and deepest of the 11 Finger Lakes in central New York State. Its watershed is an ideal natural laboratory to investigate the fluvial flux of calcium, because factors that might influence calcium delivery to the lake like subwatershed area, land use, bedrock, and soil types, systematically vary across the 19+ subwatersheds, and surface outflow is controlled by one outlet.

Weekly water samples were collected from 4 sites in the northern half of the lake and near the terminus of 6 second order and larger subwatersheds over the past few years; both were augmented with occasional samples from up to 10 additional subwatersheds. The water was analyzed for major ions by an ion chromatograph. Stream discharge was estimated by measuring the stream x-sectional areas and sectional mid-point water velocities of 5 or 10 equally spaced stream sections.

The results indicate that calcium influx is controlled by both stream discharge and concentration. Discharge correlates to subwatershed area (r²=0.43). Calcium concentration corresponds to bedrock composition (r²=0.77) and not agricultural land use (r²=0.00) as previously hypothesized. The soil composition relationship will be investigated in the future. Extrapolating these results to unsampled subwatersheds, the total fluvial influx of Ca to the lake is approximately 50,000 metric tons per year. A mass balance model using this flux and a water residence time of 18 years predicts a calcium concentration of 65 ppm in the lake. Yet, the actual lake concentration of 43 ppm is much lower than predicted, and suggests that a significant amount of calcium is removed from the water column and deposited on the lake floor as fine-grained calcite precipitated in summer whiting events, and zebra / quagga mussel shells.