DECREASING SALINITY IN SENECA LAKE, NEW YORK

Seneca Lake is more saline than the other glacially excavated Finger Lakes (e.g., Cl at 140 ppm vs. 40 ppm). Wing et al. (1995) suggested that Seneca, and to a lesser extent Cayuga Lake, has an additional groundwater source of saline water to compliment typical fluvial sources because they are deep enough to intersect the Silurian beds of commercial grade rock salt located ~450-600 m below the surface. Mass-balance arguments by Halfman et al. (2006) indicated that sodium is stoichiometrically consistent with chloride. Finally, Jolly (2006) showed that the chloride concentration has not been constant over the past century. Chloride concentrations were ~40 ppm in 1900, rose to ~170 ppm by the 1960's, and subsequently decreased since 1980 to the present day concentration of ~120 ppm. Here we focus on the decrease in concentration over the past decade.

Water samples were analyzed from 4 sites at the northern end of Seneca Lake from 2001 to present on a weekly basis during the spring-summer-fall seasons. A CTD profile of temperature, specific conductance, and other parameters versus water depth was collected at each site. In addition, filtered surface and bottom water samples were analyzed by ion chromatography for major ions (Cl, SO4, Na, K, Ca, Mg).

The CTD data revealed that surface and bottom water specific conductance were the same during the early spring and late fall when the lake was isothermal. Surface water specific conductance decreased through the year then rose at the end of the year during thermal stratification. It also showed that bottom water remained unchanged until end of the year, and decreased slightly. Surface and bottom water ion concentrations revealed similar trends. Surface and bottom water mixing during overturn resulted in a uniform lake concentration that was slightly smaller than previous bottom water and larger than previous surface water concentrations. The largest change in ion concentrations was in those ions with the largest difference between lake and tributary concentrations, e.g., chloride and sodium. A reduction of road salt use, salt mining activities or closure of salt pathways through the sediment column are the probable causes in the annual scale salinity decrease but more work is required to determine the exact cause.