Dependence of water quality and fish habitat on lake morphometry and meteorology

The dependence of lake water temperatures, dissolved oxygen concentrations and associated fish habitat characteristics on weather parameters and lake morphometry has been quantified from the output of verified water quality models. The models were applied to 27 Minnesota lake classes Lake survey data for 3,002 lakes in the Minnesota Lakes Fisheries Database were used as a basis for the classification. The one-dimensional, deterministic, process-based water quality models used 25 years of daily meteorological data (1955-79) as input. The simulated characteristics of daily water temperatures, dissolved oxygen concentrations, and fish habitat during the open water season are correlated selectively with lake surface area, maximum depth, Secchi depth, annual normal air temperature, and saturated dissolved oxygen concentration. Annual 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 water temperatures. Saturated dissolved oxygen concentration evaluated at maximum daily normal surface water temperature and lake geometry ratio were found to be good predictors 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 fish habitat as long as the upper good growth water temperature limit is not exceeded. Lakes with geometry ratios A_s^0.25/H_max < 2 are seasonally stratified, have low dissolved oxygen concentrations near the bottom in summer, and only a fraction of their total lake volume available 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 formulated from the simulation results.