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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.

Multivariate methods of trend analysis offer the potential for higher power in detecting gradual water quality changes as compared to multiple applications of umvariate tests. Simulation experiments were used to investigate the power advantages of multivariate methods for both linear model and Mann-Kendall based approaches. The experiments focused on quarterly observations of three water quality variables with no serial correlation and with several different intervariable correlation structures. The multivariate methods were generally more powerful than the univariate methods, offering the greatest advantage in situations where water quality variables were positively correlated with trends in opposing directions. For illustration, both the univariate and multivariate versions of the Mann-Kendall based tests were applied to case study data from several lakes in Maine and New York which have been sampled as part of EPA's long term monitoring study of acid precipitation effects.(KEY TERMS: trend analysis; multivariate analysis; statistics; lake water quality; acid precipitation.)

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