THERMAL STRUCTURE OF LAKES VARYING IN SIZE AND WATER CLARITY

The epilimnion depth of lakes is related both to lake size, which affe cts wind-induced mixing, and to water clarity, which affects the depth over which solar radiation heats the water. Here we attempt to isolat e the relative importance of these two variables by examining lakes th at have changed in water clarity with time (between years), by examini ng nearby lakes of comparable size, and by partitioning a large number of lakes into subsets with a restricted range in size or Secchi depth . Overall, results indicate that both lake size and water clarity are important determinants of epilimnion depth, but the absolute effect (i ndicated by slope) of Secchi depth is approximately constant in small (< 12.5 km2) as well as large lakes and the Laurentian Great Lakes, wh ile its relative importance (indicated by r2) appears to be restricted to the small lakes.