A Methodology to Estimate Global Climate Change Impacts on Lake and Stream Environmental Conditions and Fishery Resources with Application to Minnesota

Abstract

The effects of global climate were projected on the distribution and growth potential of common freshwater fishes in 5 streams and 27 classes of lakes in Minnesota. The method developed for, this analysis uses laboratory growth and mortality data, and a stream temperature-fish distribution database, to define temperature responses for 32 fish species. Sensitivity to depressed dissolved oxygen concentrations was derived from information presented in the U.S. EPA ambient water quality criteria document on oxygen. Stream and lake water temperatures and lake dissolved oxygen concentrations are simulated by one-dimensional, unsteady heat and oxygen transport models operating on a timestep of one day. Simulations are made for a 25-year historical period (1955.-80) and projected steady-state future climate simulated by general circulation models assuming a doubling of atmospheric CO2• Water temperature and dissolved oxygen (D.O.) concentrations simulated for streams and lakes are then compared to "critical" values for presence (survival ) or "good" growth (time of exposure to temperatures permitting rapid growth) of a fish species or guild. The results project expected impacts on representative Minnesota streams, while the lake results represent a regional analysis for the state as a whole. The following conclusions stand out among the many study results. In wide, essentially unshaded streams, global warming is expected to contribute to elimination of coldwater fishes and some coolwater fishes in many habitats where they were formerly present. Warmwater fishes will gain substantially more potential for good growth than existed previously. Coldwater fishes will have a chance for continued existence only in those streams with adequate shading by riparian trees. Coldwater fishes will have the best chance to survive in deep lakes located in the northern half of the state, but there will be a loss in habitat for good growth. Warmwater fishes will gain habitat for good growth in virtually all types of lakes. Coolwater fishes will gain habitat enabling good growth in most types of lakes. Losses or gains in good growth potential due to global warming are projected to be larger in deep lakes than in shallow ones. The trophic state of the water body will also have an influence on the response of indigenous fishes to climate change. In shallow lakes, trophic state is projected to have little effect on the influence of global warming on habitat suitability for fishes. In deeper, seasonally stratified eutrophic lakes losses or gains of habitat for good growth are projected to be smaller than in oligotrophic lakes of the same size and depth. Lake size and depth are of importance as they affect seasonal stratification of water temperature and dissolved oxygen. Dissolved oxygen limitations are more serious in eutrophic lakes than in oligotrophic lakes. They are also more apparent in deep lakes than in shallow ones. Climate change is projected to worsen availability of habitats for good growth due to oxygen limitations. For the state as a whole, the potentital for good growth of lake dwelling, coolwater fishes is projected to increase by 20 percent and for warmwater fishes by 53 percent. Coldwater species will lose 40 percent of their habitat suitable for good growth. The total habitat for good growth of Minnesota lake fishes, regardless of guild designation, is projected to increase by 6 percent.