WEEKLY MONITORING OF RIVER CHEMISTRY IN ST. LAWRENCE COUNTY, NEW YORK

Four rivers in the northern Adirondack region flowing into the St. Lawrence River were sampled weekly for one year (June 2011 – June 2012) for 72 elements and 7 anions. From West to East, the rivers include the Oswegatchie (OSW), Grasse (GRA), Raquette (RAQ), and St. Regis (STR). The headwaters of all the rivers begin in the acidified Adirondack Highlands (crystalline acidic bedrock) and flow across the Adirondack Lowlands (marble-rich metasedimentary sequence) and early Paleozoic sedimentary rocks (sandstone and dolostone) of the St. Lawrence River Valley. Sampling was conducted close to US Geological Survey gauging stations in the St. Lawrence River Valley so that loading of the analytes could be determined. In general, the waters were dilute: OSW (128.0±37.4), GRA (125.3±40.6), RAQ (61.8±21.7), and STR (96.1±36.2) μS. Their mean pH was 7.11±0.52, 7.62±0.66, 7.22±0.50, and 7.33±0.50. The most abundant cations were Ca, Na, Si, Mg, and K. The chief anions were carbonate, chloride, and sulfate. Mean calculated ANC values in the four rivers are 43.1±6.4, 43.6±9.0, 17.2±5.4, and 31.5±7.2 (mg/L). The chemistry of the rivers varies from west to east and is influenced by the relative proportion of their path that goes through the various geologic terrains. Soluble di- and monovalent cations (Ca²⁺, Mg²⁺, Na⁺, and K⁺) do not change in concentration seasonally or with respect to discharge. Relatively insoluble trivalent cations (Al³⁺, Fe³⁺, REE³⁺) reached their highest concentration in early summer and decreased during the remainder of the year. The chemistry of the Raquette River is clearly anomalous and has the least amount of total dissolved solids and the least seasonal variability in nearly every analyte. This homogeneity is likely related to a number (n = 17) of hydropower reservoirs along its length; some of them of considerable size and depth. On three occasions anomalous alkalinity and related chemical constituents in the Raquette River were measured. These occur on dates of significant runoff and can be explained by discharge of waters from a dolostone quarry upriver. In all the rivers Ca, Mg, and K do not change much throughout the seasons, however, Al and Fe, drop in concentration within the rivers from summer to spring. Silica reached its greatest concentration during the winter months.