The Exchange of Dissolved Substances Between Mud and Water in Lakes

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Abstract
Report of a study of the physical-chemical changes which take place at the mud-water interface in the hypolimnion of lakes and the resulting contributions of various nutritive substances to the water from the bottom deposits. Regular observations were made on Esthwaite Water, with laboratory expts. and data on other lakes obtained for comparison. 4 physical and 16 chemical factors were studied. Particular attention was given to the chemical changes taking place in the lower water after the onset of thermal stratification. As the season advanced the reduction of the O2 produced reducing conditions in this stratum as shown by the change in redox potential. Under these reducing conditions certain substances in the mud dissolved and these solutes moved upward into the water, due chiefly to eddy diffusion. Assuming that all of the solutes came from the mud, it was estimated that the mean eddy diffusion coeff. for selected levels was 20 to 2000 times the respective molecular coeffs. of heat conduction and chemical diffusion; even in winter when the lake was covered with ice, the eddy diffusion coeff. was > 200 times the molecular coeff. The reduction of the mud surface and the associated increase in the supply of solutes to the water depend upon the reducing power of the mud and the amt. of O2 supplied to the mud surface. At the time of the autumnal overturn in Oct., the solutes are distributed throughout the lake and thus become available to the phytoplankton.

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