Abstract

Sediments from a hypereutrophic sludge-disposal lake (Mitchell Lake, Texas) were analyzed for total, inorganic, organic, and bioavailable phosphorus. Total phosphorus was analyzed using two methods, the Environmental Protection Agency SW 3050B method for analyzing sludge samples and the traditional ignition method for analyzing soil samples. Both methods yielded comparable results. The ignition method generally extracted less phosphorus than the 3050B method, but the high degree of correlation between the two methods indicate that they are extracting phosphorus from the same pool. There was clear evidence of spatial variability in sediment-phosphorus concentrations caused by indiscriminant disposal of sewage sludge over time. Four chemical extraction techniques were employed to assess readily desorbable phosphorus, algae-available phosphorus (AAP), Olsen phosphorus, and Mehlich III phosphorus. Although the Mehlich III method extracted the greatest amount of phosphorus, this acid extraction method is quite possibly overestimating the bioavailable fraction caused by dissolution of the alkaline phosphate precipitates. Readily desorbable phosphorus and AAP extracted the least amounts and yielded the poorest correlations with both total and inorganic phosphorus. The Olsen method, which employs an alkaline extraction scheme, was deemed most suitable for determining phosphorus bioavailability under the specific geochemical conditions of Mitchell Lake. Hence, careful evaluation of the physicochemical properties of sediments is necessary prior to deciding on the optimal bioavailability procedure.

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