On the Kinetics of Phosphorus Exchange in Lakes

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Abstract
One thousand millicuries of radioactive phosphorus, 32P, were added to the surface of an unstratified, primitive lake of area 4 ha. (10 acres) and depth 7 m., situated near Halifax, Nova Scotia. There was a rapid loss from the water, and uptake by aquatic life and mud. As the added phosphorus increased the normal water content by only 0.25%, a mechanism of removal does not explain the results. Instead, an active exchange is postulated, between the water phosphorus and participating phosphorus in the lake solids, which together make up a single system. An equation is given to describe the equilibrium reached by an exponential decline of water phosphorus, balanced by a return from the solids, also exponential. The turnover time for the water phosphorus is calculated as 5.4 days; for the solids 39 days. The equation is applied to several other lakes where radio-phosphorus or fertilizer has been added and followed by water analyses, and also to the decline in phosphorus, following the spring maximum. The results of adding fertilizer to two marine ponds are also examined. The turnover times for water vary from 2.4 to 30 days or more, and for the solids from 37 days to at least 176 days. The relation of the results to the general problem of eutrophication is discussed.