GEOCHEMICAL CHARACTERIZATION OF POLLUTED (?) TRIBUTARY WATER DRAINING INTO BLACK LAKE, ST. LAWRENCE COUNTY, NEW YORK

Black Lake, located in western St. Lawrence County, is the largest lake (8349 acres) in the county and a popular year-round recreational (fishing, swimming, boating) spot. The land surrounding the lake is underlain by Precambrian calcitic or dolomitic marble, granitic gneiss, and Cambrian sandstone, and overlain by Quaternary silt, clay, glacial till, rock debris, and lacustrine and marine sediments. Several tributaries drain into Black Lake from watersheds containing forest, wetlands, farms, and/or developed (urbanized) areas.

Black Lake is currently classified as stressed due to the high nutrient (phosphate) levels in the lake that support massive populations of invasive weeds (Eurasion Watermilfoil) yet the exact source(s) of nutrients within the lake have not been identified. Possible sources include runoff from nearby farm fields, urbanized areas, or leaking septic systems from shore side camps.

This preliminary study focused on geochemically analyzing water within eight tributaries (ZK08-BL1, ZK08-BL3 to -BL9) that drain into Black Lake to ascertain if they are partially or wholly responsible for the elevated nutrient load in the lake. One sample of lake water (ZK08-BL2) was also analyzed. Our data show that analyte concentrations (nitrate, 5.8-16.0 mg/L; nitrite, <0.20 mg/L; sulfate, 5.8-16.0 mg/L; phosphate, <0.05-0.09; surfactants, <0.025 mg/L; Na, 2-12 mg/L; Cl, <1-20 mg/L) and pH (7.6-8.1), conductivity (80-218 mg/L) and temperature (7.9-10.8°C) for each tributary water sample are generally similar to one another, except for elevated concentrations of Na (21 mg/L) and Cl (44 mg/L) in sample ZK08-BL6 and phosphate (0.33 mg/L) in sample ZK08-BL9.

Compared to averaged concentrations of phosphate (0.04 mg/L) and nitrate (0.02 mg/L) in Black Lake water from the last 19 years, the tributary waters contain slightly elevated concentrations of each (0.09 and 0.5 mg/L, respectively). This work is ongoing as additional annual tributary and lake water samples are necessary over a several-year span to pinpoint the exact source(s) of the nutrients in the lake.