AN INVESTIGATION OF STREAM CHEMISTRY VARIABILITY IN WATERSHEDS OF CENTRAL ST. LAWRENCE COUNTY, NEW YORK

Sixty water samples from five small watersheds (<250 km²) in northern New York, were analyzed for major and trace element chemistry, major anions, acid-neutralizing capacity (ANC), and various physicochemical parameters in an effort to understand the geochemical variability in the headwaters of the Oswegatchie, Grasse, and Raquette Rivers. The data suggests that lithology, elevation, land use, wetlands/lakes, and mine drainage are locally important factors in small streams. Major lithological and land-use changes occur across the Carthage-Colton Mylonite Zone which separates Meso-Proterozoic rocks of the NW Adirondack Lowlands from the Adirondack Highlands to the SE. The Lowlands are underlain primarily by metasedimentary rocks, including abundant marble and calc-silicate gneisses, whereas the Highlands contain mostly acidic metaigneous rocks with minimal buffering capacity. ANC values were experimentally determined for all rocks types in each drainage basin, including quaternary deposits, and ranged from 82 mg CaCO₃/kg (Grenville marble) to 20.5 mg CaCO₃/kg (Cambrian Potsdam sandstone). The ANC value of each rock type was normalized to its areal extent and the relative acid neutralization capacity of each subbasin was determined. Average values for the five drainage basins ranged from 24.4 to 38.1 from the Highlands to the Lowlands and were strongly influenced by the presence of marble. The largely forested (74-84%), sparsely populated, southern portion of the county is highly impacted by acid precipitation but even within this area the extent of acidification and Al concentrations are variable and primarily a function of bedrock lithology and elevation. The effects of drainage from tailings of an abandoned iron mine strongly influence the geochemistry of several tributaries, particularly concentrations of TDS, Fe, Mn, and REEs. Stream waters draining the Adirondack Lowlands, with considerable agricultural land-use activities (19-37%), have higher pH, ANC, TDS values, and are dominated by Ca and Mg, and other soluble elements.