DOI: 10.1306/eg.10200303021

Phosphorus bioavailability in sediments of a sludge-disposal lake

¹ Earth and Environmental Science Department, University of Texas at San Antonio, 6900 N Loop 1604 West, San Antonio, Texas
² Earth and Environmental Sciences Department, University of Texas at San Antonio, 6900 N Loop 1604 W, San Antonio, Texas

John R. Branom is a graduate student in the Department of Earth and Environmental Sciences at the University of Texas at San Antonio (UTSA). Branom received his B.S. degree in marine biology from Southwest Texas State University. Branom is currently working in the Environmental Geochemistry Laboratory at UTSA with a research assistantship from the Center for Water Research. His interests are in biogeochemistry of nutrients in water and sediments and their effects on environmental quality.

Dibyendu Sarkar is an assistant professor and the director of the Environmental Geochemistry Laboratory at the University of Texas at San Antonio. Sarkar received his Ph.D. from the University of Tennessee and did his postdoctoral training at the University of Florida. His areas of expertise include soil chemistry, environmental quality and remediation, and risk assessment. Sarkar is also an associate editor of Environmental Geosciences.

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