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Westlock County AB

The influence of trophic state, thermal structure and winterkill on littoral macroinvertebrate communities in boreal plain lakes

Author(s): Langlois, P. W.

Year: 2000

Littoral macroinvertebrates were sampled from seven lakes varying in trophic state and thermal structure in north-central Alberta's Boreal Mixedwood ecoregion. Across the seven lakes, macroinvertebrate taxonomic richness was inversely related to total phosphorus concentration, and community diversity was positively related to thermal stability. Macroinvertebrate communities in less nutrient-rich, thermally stratified lakes, generally had higher relative biomass and density of amphipods and lower relative biomass and density of dipterans than communities in nutrient-rich, polymictic lakes. Total macroinvertebrate biomass was positively associated with total phosphorus concentration in stratified lakes only, suggesting that factors such as low dissolved oxygen availability negatively influence community structure in polymictic lakes. In the four study lakes with pike ( Esox lucius ) and perch (Perca flavescens ) assemblages, including one that experienced a winterkill during the study, the density of Gammarus sp. and Hyallela sp. varied inversely with fish density (either measured or projected) over time, suggesting that benthivorous fish may directly influence the density of larger, common macroinvertebrate prey. Observed relationships between littoral macroinvertebrate community structure, total phosphorus concentration, and water column thermal stability suggest that enhanced eutrophication or climatic warming could negatively affect benthic food webs in boreal lakes.