Multiple stressor effects on water quality in Poplar Bay, Lake of the Woods, Canada: a midge-based assessment of hypolimnetic oxygen conditions over the last two centuries

Chironomid and Chaoborus (midge) remains preserved in a dated sediment core from Poplar Bay, Lake of the Woods (LOW), Ontario, Canada, were used to assess the effects of multiple stressors (e.g., recent warming and shoreline development) on water quality over the past ~200 years. As monitoring data for LOW do not extend beyond recent decades, paleolimnological methods are used to reconstruct long-term limnological trends and to establish pre-disturbance conditions. The effects of recent warming and shoreline development on Poplar Bay water quality are examined using an index of hypolimnetic oxygen (O2) status based on the ratio of Chaoborus to chironomid remains (chaob:chir) and a midge-inferred volume-weighted hypolimnetic oxygen (VWHO) model. Our paleolimnological data indicate that hypolimnetic [O2] in Poplar Bay have been historically hypoxic (1-4 mg O2 L-1) but have declined further (generally