Impact of Ca(OH)2 treatment on macroinvertebrate communities in eutrophic hardwater lakes in the Boreal Plain region of Alberta: in situ and laboratory experiments

Abstract

Ca(OH)2 treatment has been recently used to remediate water quality problems associated with eutrophication in lakes on the Boreal Plain of western Canada. This study examines how Ca(OH)2 treatment affects the survival of Hyalella azteca and larvae of Chironomus spp. in laboratory microcosms and the abundance and seasonal dynamics of macroinvertebrates in two eutrophic hardwater lakes. Macroinvertebrate data for three reference lakes sampled during the same time period are also presented. Additions of 225 and 295 g Ca(OH)2·m-2 (74 and 107 mg·L-1) to two lakes resulted in lake water pH remaining within its natural range (<10) and had no discernable effects on macroinvertebrate density or biomass up to 2 years after treatment. Macroinvertebrate response to Ca(OH)2 in hardwater lakes differed markedly from results reported for softwater lakes. After 4 days, no detectable influence was observed on survivorship of Chironomus spp. with laboratory dosages of 0-300 g Ca(OH)2·m-2 (0-1781 mg·L-1), but survivorship of H. azteca was reduced by >= 50% at dosages that raised water pH to >=10 (300 g Ca(OH)2·m-2). The sensitivity of H. azteca, but not Chironomus spp., could be a result of singular or combined effects of Ca(OH)2 levels, precipitate, or changes in pH. It may also reflect the greater dependence of H. azteca than Chironomus spp on the water above, rather than below, the sediment-water interface.