Effects of winter surface aeration on pelagic zooplankton communities in a small boreal foothills lake of Alberta, Canada

Winter aeration is often used to prevent fish winter-kill among lakes supporting recreational fisheries and is often used in conjunction with trout stocking as trout are sensitive to hypoxia. We collected limnological data as well as pelagic microcrustacea and rotifers one year before and one year after aeration was initiated in Birch Lake, located in the boreal foothills ecozone of Alberta, Canada. Using a Before-After-Control-Impact design, we compared changes in Birch Lake to those in two nearby and similarly mesotrophic, stocked control lakes (one aerated for more than six years, one unaerated). During winter, surface aeration increased the depth of well-mixed water in Birch Lake, maintaining levels of dissolved oxygen suitable for supporting stocked trout. Linear mixed model analyses indicated that among May–August water quality parameters, only phosphorus concentrations showed a marginally significant treatment × year interaction, increasing only in the unaerated control lake. Aeration did not affect the spring–summer abundance, biomass, or sizes of Birch Lake's zooplankton community. Once aerated, the microcrustacean community in Birch Lake showed partial overlap with the community in the aerated control, although this could not be statistically linked to changes in specific taxa. Ours is the first study to investigate impacts of winter surface aeration on zooplankton communities despite the numerous lakes managed under this strategy.