Major Ion Chemistry of Lakes on the Kenai Peninsula, Alaska

Abstract

We characterized the major ion chemistry of over 800 lakes on the Kenai Peninsula, Alaska, from a probability sample of 59 lakes (August 1988). There were two groups: alkalinity < 300 μeq/L (78% of the lakes) and alkalinity > 700 μeq/L. Low-alkalinity lakes had significantly lower concentrations of base cations and silica and significantly higher average concentrations of dissolved organic carbon (DOC) than high-alkalinity lakes. Despite widespread acidic soils and bog vegetation, and resulting high DOC concentrations, none of the lakes sampled was acidic. Sulfate concentrations (~3 μeq/L) were similar in the two groups, as were Cl− concentrations, which decreased with distance from the coast. High-alkalinity lakes were similar chemically to rivers and shallow aquifers in the region, suggesting that the high alkalinity 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.