Lime Treatment of a Hardwater Lake to Reduce Eutrophication

ABSTRACT

Lime addition was evaluated as a lake rehabilitation technique in Frisken Lake, a naturally eutrophic hardwater lake in British Columbia. Adding 39 tonnes of calcium hydroxide in 1983 and 1984 precipitated more than 85 to 95 percent of the chlorophyll a and 89 to 96 percent of the soluble reactive phosphorus from the epilimnion. The lake was not treated in 1985 but chlorophyll a concentrations were less than those observed prior to lime treatment. Apparently lime addition did not induce phosphorus limitation; soluble reactive phosphorus concentrations in 1984 were never less than 35 μg/L. After lime treatment, phosphorus was adsorbed to calcite in the epilimnion but not in the hypolimnion; moreover, the monitoring data indicated all the precipitated phosphorus redissolved. The additional calcium carbonate precipitate may redissolve and reprecipitate as conditions change; thus, a long-term mechanism for continual algal removal was established.