MAJOR ION CHEMISTRY OF LAKES ON THE KENAI PENINSULA, ALASKA

We characterized the major ion chemistry of over 800 lakes on the Kena i Peninsula, Alaska, from a probability sample of 59 lakes (August 198 8). There were two groups: alkalinity < 300 mueq/L (78% of the lakes) and alkalinity > 700 mueq/L. Low-alkalinity lakes had significantly lo wer concentrations of base cations and silica and significantly higher average concentrations of dissolved organic carbon (DOC) than high-al kalinity lakes. Despite widespread acidic soils and bog vegetation, an d resulting high DOC concentrations, none of the lakes sampled was aci dic. Sulfate concentrations (approximately 3 mueq/L) were similar in t he two groups, as were Cl- concentrations, which decreased with distan ce from the coast. High-alkalinity lakes were similar chemically to ri vers and shallow aquifers in the region, suggesting that the high alka linity is a product of the major weathering reactions in this terrain; the substantially different ratios of base cations in the two groups also indicate quantitative and qualitative weathering differences. Low -alkalinity lakes were at higher elevations than high-alkalinity lakes , presumably in groundwater recharge zones. Consequently, the chemical differences between the two lake groups appeared to be controlled by relatively small differences in local hydrologic setting, and possibly by differences in mineralogy along the groundwater flowpaths.