Anthropogenic stressor impacts on hypolimnetic dissolved oxygen in Lake Erie: A chironomid-based paleolimnological assessment

The central basin of Lake Erie is annually subject to hypolimnetic hypoxia, which affects biochemical processes and aquatic biota. Since European settlement, water quality in Lake Erie has degraded due to land-use changes within its catchment, cultural eutrophication, climate change, and the effects of invasive species. As limnological monitoring data for Lake Erie are largely unavailable prior to the 1970s, paleolimnological methods were used to infer long-term trends in hypolimnetic dissolved oxygen. Changes in lake water quality affect benthic community composition, and those communities can be used as indicators of long-term environmental changes, particularly those that affect hypolimnetic oxygen concentrations. Chironomid subfossil remains preserved in dated sediment cores indicated that the hypolimnion of the central basin was exhibiting low oxygen conditions prior to major Euro-American settlement impacts, and it has been mesotrophic to eutrophic since ∼1850. The disappearance of oxic-type taxa and a transition towards anoxic-tolerant chironomid communities by the 1950s suggest that the severity and duration of hypolimnetic anoxia has increased in recent decades. Variance partitioning analysis (VPA) indicated that both land use and climate variables were significant drivers of these changes in chironomid assemblages in the central basin.