Chemical Response of Lakes Treated with CaCO₃ to Reacidification

Abstract

The reacidification of two lakes in the Adirondack region of New York treated by CaCO 3 application was evaluated. Base treatment resulted in a very high immediate dissolution efficiency in both lakes (78–82%), increasing acid neutralizing capacity (ANC) to values of 450–550 μeq∙L −1 . During the fall following manipulation, completely mixed water columns and elevated hydrologic inputs greatly facilitated reacidification, decreasing pH and diluting Ca 2+ concentrations. Cranberry Pond effectively reacidified within 7 mo of treatment, while the ANC of Woods Lake decreased to near 0 μeq∙L −1 15 mo after application. In Cranberry Pond, pH values decreased below 5.5 resulting in transport of elevated concentrations of inorganic Al through the lake. Annual ANC budgets suggest that little CaCO 3 penetrated to the sediments, limiting long-term release of ANC from sediment dissolution. Hydrolysis of Al, due to the elevated lake pH, served to consume ANC and there is evidence to indicate limited exchange of water column Ca 2+ with sediments shortly after treatment followed by release of this Ca 2+ during reacidification. However these processes did not significantly accelerate or attenuate the rate of reacidification. The rate of acidification could largely be explained by the flushing of ANC from the lakes by hydrologic inputs.