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Description
A preliminary study addresses the sensitivities to acidification of four lakes in San Diego County, California and Lake Tahoe. Addition of strong acids to those lakes does not necessarily result in a concomitant drop in pH of the water-sediment systems. Buffering reactions which release cations from the sediment in exchange for the incoming acidic protons possess both immediate and long term time scales and can conceivably create pH rises after acidification of the lake systems. Two of the lakes, Hodges and Cuyamaca, contain abundant expandable clays derived from gabbroic rocks, which allow substantial acid-buffering via the release of magnesium and iron. Lake Murray, devoid of clay-size sediments, contains a large proportion of carbonates, in the form of calcite mollusks, as well as calcic and sodic plagioclases which supply the water-sediment system with abundant cations for the buffering of influxing acidic protons. In Lake Tahoe, alkalinity values of the lake-water, in combination with that lake's large volume, and low sediment to water ratios, suggest that alkalinity buffering is a viable method of acid neutralization. Lake Morena, whose sediments contain less than one percent expandable clays, and may be the most susceptible to acidification of the lakes studied, nevertheless is observed to release significant quantities of calcium and potassium upon acidification. Lake Morena's water fraction contains sufficient alkalinity to provide further buffering capacity. Hence, Lake Morena may possess its own distinct acid-neutralizing capacity. In all the lakes studied, however, heavy metals, such as iron and aluminum, are likely to be released in the event of acidification to pH's of approximately 3.0. Therefore, while acidification of these systems may not pose a threat to the lake ecosystems in the form of dangerous pH-level changes, a danger may exist in the release of toxic heavy metals.
