. Chemical composition of rivers and lakes. Water -- Composition; Rivers; Lakes. CHEMICAL COMPOSITION OF RIVERS AND LAKES G9 EXPLANATION. Fioube 3.—Seasonal changes in the chemical composition of Imikpuk, a small lake in Alaska near the Arctic Ocean. After Boyd (1959). Reprinted by permission of Ecology. Such seasonal changes are of rather restricted extent. In most lakes the major ions, except the components of the carbonate buffer system, remain relatively constant in amount, and large changes in water chemistry are restricted to the scarcer biologi- cally important substances. There are als
. Chemical composition of rivers and lakes. Water -- Composition; Rivers; Lakes. CHEMICAL COMPOSITION OF RIVERS AND LAKES G9 EXPLANATION. Fioube 3.—Seasonal changes in the chemical composition of Imikpuk, a small lake in Alaska near the Arctic Ocean. After Boyd (1959). Reprinted by permission of Ecology. Such seasonal changes are of rather restricted extent. In most lakes the major ions, except the components of the carbonate buffer system, remain relatively constant in amount, and large changes in water chemistry are restricted to the scarcer biologi- cally important substances. There are also diurnal changes in water chemistry, but these are known to involve only the dissolved gases, oxygen and carbon dioxide. During the day, photosynthetic plants remove carbon dioxide from the water and use it in the manufacture of carbohydrate, giving up oxygen at the same time. During the night the respiration of plants and animals reverses the process. In very productive lakes, under the control of carbo- nate buffer systems, uptake of carbon dioxide by photosynthesizing plants occasionally may cause very dramatic changes in pH, as first the free C02, then the HC03, and finally carbonate is used in photosynthesis. The latter step is accomplished by the hydrolysis of calcium carbonate, and leaves calcium hydroxide in the water. An example is given in figure 4. Oxygen is easily and accurately measured, and forms part of a great number of chemical analyses of lake waters and of river waters as well. Most of these have been spot analyses taken at a single and unspecified time of day, and yield very little information of value about the oxygen content of the water over a period of 24 hours. Eecently there has been much interest among limnologists in using diurnal oxygen change as a measure of biological productivity (fig. 5), and one may expect a great increase in the amount of informa- tion about the magnitude of changes in this gas. At present it is evident that the change is g
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