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.
Office of Program Planning and Evaluation, US Environmental Protection Agency
Stefan, Heinz G.; Hondzo, M.; Sinokrot, Bashar; Fang, Xing.
A Methodology to Estimate Global Climate Change Impacts on Lake and Stream Environmental Conditions and Fishery Resources with Application to Minnesota.
St. Anthony Falls Hydraulic Laboratory.
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