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Effects of hypolimnetic aeration on functional components of the lake ecosystem Ashley, Kenneth Ian


The whole-lake experimental approach was used to examine the effect of hypolimnetic aeration on several key components of the lake ecosystem. These included circulation and decomposition processes, major nutrient, ion and-pH interactions as well as phytoplankton and zooplankton populations. A small (3.9 ha, Z max.=9.0 m) naturally eutrophic lake was divided into experimental and control halves by a plastic curtain, and a hypolimnetic aerator installed in the experimental half and operated from April 1978 to March 1979. Hypolimnetic aeration had no effect on thermal stratification during the ice-free season but circulated the entire experimental half under ice cover. Aeration increased hypolimnetic turbidity but did not affect epilimnetic transparency. Hypolimnetic oxygen levels were increased along with a ten fold rise in oxygen consumption. Hypolimnetic ammonia levels were reduced and sufficient oxygen was added for nitrification to occur. Internal phosphorous loading and hypolimnetic orthophosphate levels were also reduced however aerobic P regeneration, increased. Aeration vented accumulated CO₂ from the hypolimnion and decreased its calcium, magnesium, bicarbonate and orthophosphate content via calcium carbonate coprecipitation. Phytoplankton abundance and species composition (averaged over the water column) were not affected by hypolimnetic aeration. The zooplankton community exhibited similar vertical distribution on both halves of the lake however greater numbers were found on the experimental half after several months aeration. Management implications of hypolimnetic aeration are also discussed.

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