|Name||Miss Kathleen McCormac|
|Organization or Institution||University of Central Florida|
Extraction and Quantification of Phosphorous in Lake Sediments
Kathleen R. McCormac and Melanie J. Beazley
University of Central Florida
Understanding the bioavailability of phosphorus (P) in freshwater lakes is important to controlling algal blooms and meeting environmental regulation requirements. The chemical speciation of P in lake sediments plays an important role in determining whether P will remain buried or diffuse back into the water column and become bioavailable for algae. A chemical sequential extraction technique for sediment P will be presented with quantification by ion chromatography (IC) and inductively coupled plasma mass spectrometry (ICP-MS). Changes in the seasonal P speciation within lake sediments was determined including organic, precipitated, and adsorbed forms of P. Lake water column depth and sediment type played an important role in P speciation and concentration. Shallow sediments contained a higher fraction of adsorbed P in sandy, silty grains compared to higher fractions of organic P in deeper, more organic-rich sediments. Additionally, reduction/oxidation reactions within lake sediments played an important role in P chemical speciation. Iron and manganese concentrations determined from porewater ICP-MS measurements demonstrated a redox active zone within the top 4 cm below the sediment-water interface. Reduction of iron (III) oxyhydroxides to iron (II) oxides released adsorbed orthophosphate from iron surfaces filling sediment pore spaces with bioavailable P, which was not observed to be released back into the water column. The occurrence of aluminum phosphate solid-phase minerals in x-ray diffraction (XRD) patterns of sediments suggest that released P from iron surfaces re-adsorbed to non-redox active aluminum mineral surfaces.