DEPENDENCE OF WATER-QUALITY AND FISH HABITAT ON LAKE MORPHOMETRY AND METEOROLOGY

The dependence of lake water temperatures, dissolved oxygen concentrat ions, and associated fish habitat characteristics on weather parameter s and lake morphometry has been quantified from the output of verified water quality models. The models were applied to 27 Minnesota lake cl asses, Lake survey data for 3,002 lakes in the Minnesota Lakes Fisheri es Database were used as a basis for the classification. The one-dimen sional, deterministic, process-based water quality models used 25 year s of daily meteorological data (1955-79) as input. The simulated chara cteristics of daily water temperatures, dissolved oxygen concentration s, and fish habitat during the open water: season are correlated selec tively with lake surface area, maximum depth, Secchi depth, annual nor mal air temperature, and saturated dissolved oxygen concentration. Ann ual normal air temperature and lake geometry ratio (the fourth root of lake surface area A, divided by the maximum lake depth H-max; A(s)(0. 25)/H-max) were found to be good predictors for simulated daily normal (25-year average) surface water temperatures, water temperatures near lake sediments, and volume-averaged wafer temperatures, Saturated dis solved oxygen concentration evaluated at maximum daily normal surface water temperature and take geometry ratio were found to be good predic tors for simulated daily normal surface and volume-averaged dissolved oxygen concentrations. Lakes with geometry ratios A(s)(0.25)/H-max > 8 are well mixed, have high dissolved oxygen concentrations, and good f ish habitat as long as the upper good growth water temperature limit i s not exceeded. Lakes with geometry ratios A(s)(0.25)/H-max < 2 are se asonally stratified, have low dissolved oxygen concentrations near the bottom in summer, and only a fraction of their total lake volume avai lable for good growth of fishes. Empirical formulas for indicators of lake water temperatures, dissolved oxygen, and associated fish habitat as functions of weather and morphometric lake parameters are formulat ed from the simulation results.