IMPACT OF OVERFLOWS ON ACID-BASE CHEMISTRY IN LIMED LAKES

During the winter ice-cover an inverse thermal stratification arises in dimictic lakes because cold surface water overlays the warmer and deeper lake water owing to differences in density. This condition can create so-called overflows in lakes, with the result that cold inflow water will only mix with the surface water immediately below the ice-cover. Changes in acid-base chemistry in limed lakes in SW Sweden showed that these overflows occurred in the winters of 1983-1986, creating acidifying surges in surface and outflow water. A comparative study of the course of dilution and measured Ca-concentrations/alkalinity in the outflows indicates that the overflows occurred down to depths of 1.5-2 m below the ice, apart from two brief periods. In April 1985 and January 1986 the overflow depth was estimated to be 0.5 m. The impact of acid overflows on surface water chemistry in limed lakes depends on the depth of the overflow as well as the retention time and mean depth of the lake. “Complete abstract not presented.”