Impact of Lime on Sediment Phosphorus Release in Hard water Lakes: the Case of Hypereutrophic Halfmoon Lake, Alberta

Abstract

ABSTRACT Halfmoon Lake is a small, moderately deep, hypereutrophic, hardwater lake with a relatively small (2.4 km2), partially cleared drainage basin situated in the Boreal Mixedwood Ecoregion of central Alberta. The water is often thermally stratified, and average residence time is 60 years. During mid- to late summer 1988 and 1989, 188 metric tons of Ca(OH)2 and 58 metric tons of CaCO3 were applied to the surface of Halfmoon Lake to decrease total phosphorus (TP) concentration and algal biomass (estimated as chlorophyll a [Chl a]). Mean summer (July-September) Chl a and TP in the euphotic zone in 1989 and 1990 decreased to 53 and 63%, respectively, of the pretreatment year (1982). Similarly, sediment P release from June through August was 50% lower in 1989 and 1990 than in the pretreatment year. In contrast water quality deteriorated in three nearby reference lake basins, also hypereutrophic, so that average summer euphotic zone Chl a and TP were 217 and 116% higher, respectively, in 1989 and 1990 than...