Cultural eutrophication, anoxia, and ecosystem recovery in Meretta Lake, High Arctic Canada

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Abstract
We studied the effects of four decades of cultural eutrophication on Meretta Lake, in the Canadian High Arctic, through a multiproxy analysis of its sediments, including sedimentary pigments, metal concentrations, stable isotope ratios, chironomids, and diatoms. While Meretta Lake's biota clearly responded to nutrient inputs, the manner in which the changes differed from those expected in temperate lakes underlined the profound effects in Arctic lakes of extended ice and snow cover on light penetration, mixing, and interactions with the atmosphere. Hypolimnetic anoxia developed rapidly in Meretta Lake in response to sewage enrichment and was accompanied by the appearance of photosynthetic sulfur bacteria. Benthic communities responded rapidly to sewage inputs, but phytoplankton biomass did not increase until eutrophication was accompanied by climate warming, further reinforcing the importance of ice cover in controlling biotic processes in high Arctic lakes. With climate‐mediated ice cover reductions in Meretta Lake, the response to eutrophication began to more closely resemble temperate processes. Recent trajectories indicate that slightly more than a decade after the cessation of sewage inputs, Meretta Lake is recovering toward pre‐enrichment conditions.

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