Radiochemical Analysis of Orthophosphate Concentrations and Seasonal Changes in the Flux of Orthophosphate to Seston in Two Canadian Shield Lakes

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Abstract
Seasonal changes in the concentration and dynamics of phosphate–phosphorus were studied in two small lakes, one oligotrophic and one artificially eutrophied. Because the molybdate blue phosphate technique frequently overestimates phosphate concentrations, three radiochemical assays were used. One, involving sephadex fractionation, was unsatisfactory because of the long period required for high molecular weight phosphorus fractions to reach isotopic equilibrium. The second method was unusable both for epilimnion waters within the Experimental Lakes Area, because of its low sensitivity, and for hypolimnion waters, due to interference from nonphosphate compounds. The third method, Rigler's bioassay, indicated that PO4-P in both lakes seldom exceeded 0.1 μg∙L−1, even under anoxic conditions. Organisms, and not mineral reactions, appeared to regulate the phosphate concentration at all depths in the lakes.Key words: phosphorus dynamics, orthophosphate

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