Simulated Fish Habitat Changes in North American Lakes in Response to Projected Climate Warming

Fish habitat is strongly constrained by water temperature and the available dissolved oxygen (DO). Fish habitat in small lakes of the contiguous United States was therefore determined from simulated daily water temperature and dissolved oxygen profiles. Twenty-seven types of lakes were simulated under past (1962–1979) climate conditions and a projected doubling of atmospheric carbon dioxide (2×CO2 climate scenario) at 209 locations in the contiguous United States. The 2×CO2 climate scenario was derived from the output of the Canadian Climate Centre's General Circulation Model for a doubling of atmospheric CO2. A verified, process-oriented, dynamic, one-dimensional (vertical) lake water quality model (MINLAKE96) was used for the temperature and DO simulations, which were run in a continuous mode over a 19-year simulation period. Water temperature and DO criteria for the survival and good growth of three fish guilds (cold-, cool-, and warmwater fish) were provided by the U.S. Environmental Protection Agency. Winterkill, which occurs in the eutrophic and mesotrophic shallow lakes of the northcentral and northeastern states under present climate conditions, is projected to disappear under the 2×CO2 climate scenario due to a shortening of the ice cover period. While coldwater fish habitat is projected to persist in deep lakes near the northern border of the United States, it is likely to be eliminated from almost all shallow lakes in the contiguous states. Climate warming is projected to reduce the number of locations in the contiguous United States where lakes have suitable coldwater and coolwater fish habitat by up to 45% and 30%, respectively. Summerkill under the 2×CO2 climate scenario is projected to have a significant negative influence on northern lakes and on coolwater fish in southern lakes where suitable habitat existed under historical conditions. The largest negative impact of climate warming on coldwater fish habitat occurs in medium-depth lakes (maximum depth of 13 m); the largest negative impact on coolwater fish habitat occurs in shallow lakes (maximum depth of 4 m). Warmwater fish habitat is projected to be extended in all lakes investigated. Under the 2×CO2 climate scenario, good-growth periods are projected to increase by 37 d (average of 209 locations) for coolwater fishes (with a standard deviation of 30 d depending on lake type) and by 40 d for warmwater fishes (with a standard deviation of 34 d).