Effects of Calcite Treatment on Primary Producers in Acidified Adirondack Lakes. II. Short-Term Response by Phytoplankton Communities

The effects of calcite addition on two acidic Adirondack lakes were studied by investigators participating in the Lake Acidification Mitigation Project. Changes in phytoplankton biomass, productivity, and species composition were monitored during the ice-free period prior to and following lake treatment. Changes in water chemistry following limestone addition were largely restricted to the upper water column since calcite particles applied to the lake surface did not effectively penetrate the thermocline. Increased phytoplankton production and biomass were observed during the posttreatment period. Phytoplankton densities and rates of production were similar in both the neutralized (pH > 7.5) and acidic (pH < 5.5) portions of the water column; however, species composition was markedly different. The phytoplankton assemblage of the upper water column was largely comprised of chlorophytes and chrysophytes which had not been observed prior to treatment. In contrast, the deep-water assemblage comprised many of the same taxa that had been dominant during the pretreatment periodsss.