Simulation and validation of fish thermal DO habitat in north-central US lakes under different climate scenarios

Fish habitat in lakes is strongly constrained by water temperature and available dissolved oxygen (DO). Suitable fish habitat for three fish assemblages (cold-, cool-, and warm-water) in Minnesota (US) lakes was therefore determined from simulated daily water temperature and dissolved oxygen profiles. A total of 27 types of lakes were simulated under past (1961–1979) and a projected 2×CO2 climate scenarios. The projected climate scenario was derived from the output of the Canadian Climate Center General Circulation Model for a doubling of atmospheric CO2. A verified, process-oriented, unsteady and one-dimensional (vertical) year-round lake water quality model (minlake96) was used for the temperature and DO simulations, which were run in a continuous mode over 19 years. Water temperature and DO criteria for survival and good-growth of each fish guild were provided by the United States Environmental Protection Agency. Simulated suitable fish habitats were compared with fish observations in 3002 Minnesota lakes. Winterkill was simulated to occur in shallow eutrophic and mesotrophic lakes under past climate conditions, and predicted to disappear under the projected 2×CO2 climate scenario due to a shortening of the ice cover period. Sensitivity of the simulated winterkill to three DO survival limits was analyzed. A lower DO (less than 0.5 mg/1) limit for winterkill produced better agreement with a fish observation database than higher limits. Dependence of the simulated good-growth habitat areas (GGHA) and volumes (GGHV) on the geometry (surface area and maximum depth) and trophic state of a lake was also examined. Fish habitat parameters were found to depend more strongly on geometry and less on trophic state. Climate change is projected to increase GGHA in seasonaly stratified (medium-depth and deep) lakes on the average by 50 and 115% for cool-water and warm-water fish guilds, respectively. It is also projected that cold-water fish species will have a small percentage loss in weakly stratified (medium-depth) lakes, but a small percentage gain of GGHA in deep, strongly stratified lakes.