INTRUSION OF SALINE GROUNDWATER INTO SENECA LAKE, NEW YORK

Seneca Lake has chloride levels 2 to 10 times higher than the other Finger Lakes of central New York State despite a similar pattern of land use throughout the region. Wing et al. (1995) hypothesized that the excess salts (~170 x 10⁶ kg / year) enter Seneca Lake from below, originating from the Silurian Evaporites (rock salt) below the present lake floor. In support, Wing noted that (1) the bedrock floor is deep enough in Seneca Lake to intersect the rock salt formation under the lake but not deep enough in the other Finger Lakes, (2) the deep water mass in Seneca Lake gets saltier from the bottom up during the stratified months of the year, and (3) sediment pore waters contain larger salt concentrations with burial depth below the sediment water interface in selected sediment cores.

Here we present chloride and sodium ion analyses of lake and stream samples periodically collected over the past few years to determine if sodium concentrations support the Wing hypothesis. Sodium concentrations determined to date parallel chloride trends and strongly suggest a common hydrogeochemistry. For example, individual sodium concentrations are stoichiometrically equal to chloride on 1:1 molar basis. Seneca Lake has approximately four times more sodium ions than the local streams and the other Finger Lakes (average of 82 ± 2 ppm vs. 20 ± 11 ppm, respectively). Finally, chloride data collected over the past decade reveal similar lake concentrations over time, suggestive of a long-term, steady state situation. We plan to continue the stream and water analyses, and analyze sediment pore waters of a number of cores this fall.