Phosphorus assessment in a sludge disposal lake.

摘要

Sediments from a hypereutrophic sludge-disposal lake (Mitchell Lake, TX) were analyzed for total, inorganic, organic, and bioavailable phosphorus. Total phosphorus was analyzed using two methods, the EPA SW 3050-B 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 they are extracting phosphorus from the same pool. There was clear evidence of spatial variability in sediment phosphorus concentrations due to indiscriminant disposal of sewage sludge over time. Four chemical extraction techniques were employed to assess readily desorbable phosphorus (RDP), algal 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 possibly overestimating the bioavailable fraction due to dissolution of alkaline phosphate precipitates. RDP and AAP extracted the least amounts and yielded the poorest correlations with both total and inorganic phosphorus. The Olsen method was deemed most suitable for determining phosphorus bioavailability under the specific geochemical conditions of Mitchell Lake. The majority of P extracted by the sequential extraction method was in the HCl fraction, i.e., Ca/Mg-bound form. Very little P was extracted in either the NH4Cl (i.e., exchangeable) or NaOH (i.e., Fe/Al-bound) fractions. Sediment resuspension results showed that the majority of SRP was released within the first 12 hours. Substantially more SRP was released at moderate wind speed compared to calm simulated wind speed.