Response of plankton communities to whole-lake Ca(OH)(2) and CaCO3 additions in eutrophic hardwater lakes

1. The impact of whole-lake lime (slaked lime, Ca(OH)(2), and/or calcite, C aCO3) addition on plankton communities was evaluated in eutrophic hardwater lakes on the North American Boreal Plain. 2. Two lakes received a single treatment of lime (Ca(OH)(2) at 74 or 107 mg L-1), two lakes received multiple treatments with Ca(OH)(2) and/or CaCO3 ( 5-78 mg L-1), and four lakes were untreated and served as reference systems . 3. Over the long-term (> 1 year), phytoplankton biomass was reduced in mult iple-dose lakes, but not in single-dose lakes. Cyanobacteria typically domi nated the algal community in the years before, during and after lime treatm ent in both single- and multiple-dose lakes. 4. In the single-dose lakes, randomized intervention analysis showed no sig nificant change in the biomass of zooplankton after lime addition.