A paleolimnological assessment of coldwater fish habitat quality in Lake Simcoe, Ontario

Paleolimnological techniques (Chironomidae-based inferences of hypolimnetic oxygen, Daphnia-based inferences of fish abundance) were used to infer historic fluctuations in coldwater fish habitat quality in Lake Simcoe, a large freshwater lake with a substantial fishery currently suffering from low natural fish recruitment. Paleolimnological inferences provide information on pre-European settlement (pre-1820 AD) ecological conditions in Lake Simcoe, and identify the timing and relative influence of long-term multiple anthropogenic disturbances on Lake Simcoe's ecosystem. Paleolimnological inferences suggest pre-disturbance hypolimnetic oxygen concentrations were above 7 mg O2·L-1, which are optimal conditions for coldwater fish populations. Fish habitat quality declined during initial watershed clearance (∼1820-1890 AD), however, the largest declines correspond to urban development (∼1960-1990 AD). Inferences indicate recent (post-2000 AD) modest improvements in water quality, which corresponds to the implementation of phosphorus loading reductions as part of a lake remediation plan, however water quality conditions are still degraded relative to pre-disturbance conditions.