Zooplankton Communities In Precambrian Shield Lakes (Quebec, Canada): Responses To Spatial And Temporal Gradients In Water Chemistry And Climate

Zooplankton are relevant indicators of changes in lake water quality, used for monitoring the response of aquatic ecosystems to the combined effects of declining acidic deposition and rising air temperatures. First, the current landscape was defined from the recent (2017) spatial patterns of zooplankton communities in 73 Quebec lakes distributed over an 800-km SW-NE gradient, spanning a wide range of water quality, climate, and morphometric characteristics. On a large scale, we identified among-lake clustering of three types of zooplankton assemblages and variation in species composition at fine scale between lake pairs. Dissimilarity in zooplankton assemblages among lake pairs were best correlated (r > 0.400, p < 0.001) with their difference in air temperature, pH, and calcium, reflecting spatial gradients in climate and lake acid-base status. Second, to examine long-term response in the zooplankton community, we compared acidification indicators and abundance of taxa for a subset of 19 lakes sampled in 1982 and 2017. Despite an average threefold drop in sulfate concentration, changes in calcium and pH were relatively small, and consequently, no major changes in zooplankton assemblages were detected since 1982.