RESEARCH: Projected Climate Change Effects on Winterkill in Shallow Lakes in the Northern United States.

/ Each winter, hundreds of ice-covered, shallow lakes in the northern United States are aerated to prevent winterkill, the death of fish due to oxygen depletion under the ice. How will the projected climate warming influence winterkill and the need to artificially aerate lakes? To answer this question, a deterministic, one-dimensional year-round water quality model, which simulates daily dissolved oxygen (DO) profiles and associated water temperatures as well as ice/snow covers on lakes, was applied. Past and projected climate scenarios were investigated. The lake parameters required as model input are surface area, maximum depth, and Secchi depth as a measure of radiation attenuation and trophic state. The model is driven by daily weather data. Weather records from 209 stations in the contiguous United States for the period 1961-1979 were used to represent past climate conditions. The projected climate change due to a doubling of atmospheric CO(2) was obtained from the output of the Canadian Climate Center General Circulation Model. To illustrate the effect of projected climate change on lake DO characteristics, we present herein DO information simulated, respectively, with inputs of past climate conditions (1961-1979) and with a projected 2 x CO(2) climate scenario, as well as differences of those values. Specific parameters obtained were minimum under-ice and lake bottom DO concentration in winter, duration of under-ice anoxic conditions (<0.1 mg/liter) and low DO conditions (<3 mg/liter), and percentage of anoxic and low DO lake volumes during the ice cover period. Under current climate conditions winterkill occurs typically in shallow eutrophic lakes of the northern contiguous United States. Climate warming is projected to eliminate winterkill in these lakes. This would be a positive effect of climate warming. Fish species under ice may still experience periods of stress and zero growth due to low DO (<3 mg/liter) conditions under projected climate warming.