Thermal stratification and annual heat budget of a Florida sinkhole lake

Summary

Aerial photographs of the Florida landscape, an area of Karst topography, show the country-side to be pockmarked by small lakes, many of which are nearly circular in surface outline. Lake Mize is quite typical of these sinkhole or doline lakes in its morphometric features, including its “morning glory” basin shape. The deeper portion of the basin occupies a relatively small fraction of the area and volume of the lake. Lake Mize becomes stably stratified at superficial depths in early spring and remains so until late fall or early winter. Even the violent winds of a hurricane are insufficiently strong to break up the stratification. Stratification disappears by December and the lake circulates through the winter months during which the water temperature drops to the winter low-generally near 11° C. The circulation pattern is typical of subtropical or warm monomictic lakes-a single, extended period of circulation with the minimum temperature always well above 4° C.

Lake Mize has an extremely small annual heat budget. Based upon empirical evidence this is due to a number of factors including latitude (ca 30° N latitude), altitude (ca 30 m above sea level), protected location of the lake, small surface area and restricted solar heating. However, the regression equations of GORHAM relating annual heat budgets to various morphometric parameters of larger temperate zone lakes are not useful for predicting the annual heat budget of a lake such as Lake Mize. Year to year variations in the annual heat budget were rather large, ranging from a low of 3767 cal/cm² to a high of 6003 calf cm², so that the highest annual heat budget was roughly 1.6X that for the lowest of the three years. One expects a fair amount of year to year variation in annual heat budgets based upon Hutchinson's discussion (1957). Since we are dealing with an extremely small annual heat budget small changes are magnified when viewed on a percentage basis.