The Heat Budget of Lakes

Abstract

One of the most important and interesting characteristics of a lake is its thermal structure. The heat content of a body of water is of vital importance in limnology. The metabolism, physiology, and behavior of aquatic organisms are related directly to the temperature of the aquatic environment. Extreme temperatures restrict the growth and distribution of plants, animals, and microbes. Because of the high specific heat of water, large volumes of water change temperature relatively slowly. Therefore, large lakes tend to moderate local climates, provide longer growing seasons for aquatic life, and serve as integrated recorders of recent climatic phenomena. For these and other reasons, the thermal structure and heat content of a body of water must be known with some degree of accuracy in limnological studies.

Temperature is related to the heat content of a body of water but does not measure it. Tem­perature is a measure of the intensity of heat stored in a volume of water, not a measure of the amount of heat stored. Heat (H) is mea­sured in calories and is a function of the mass (M) of the substance in grams, temperature (t) in °C, and the specific heat (s) in cal/g-°C;^†

$$ H = M \times t \times s $$

A bathtub filled with water at 0.5°C has a much greater heat content than does a glass filled with water at a temperature of 25°C.

The use of the word “budget,” as normally defined, is incorrect but the term is firmly entrenched in the literature of limnology. Reference is to the heat storage capacity of a lake.