Characterization of Organic Phosphorus in Lake Sediments by Sequential Fractionation and Enzymatic Hydrolysis

The role of sediment-bound organic phosphorus (P-o) on lake eutrophication was studied using sequential extraction and enzymatic hydrolysis by collecting sediments from Dianchi Lake, China. Bioavailable Po species including labile monoester P, diester P, and phytate-like P were identified in the sequential extractions by H2O, NaHCO3, and NaOH. For the H2O-P-o, 36.7% (average) was labile monoester P, 14.8% was diester P, and 69.9% was phytate-like P. In NaHCO3-P-o, 19.9% was labile monoester P, 17.5% was diester P, and 58.8% was phytate-like P. For NaOH-P-o, 25.6% was labile monoester P, 7.9% was diester P, and 35.9% was phytate-like P. Labile monoester P was active to support growth of algae to form blooms. Diester P mainly distributed in labile H2O and NaHCO3 fractions was readily available to cyanobacteria. Phytate-like P represents a major portion of the Po in the NaOH fractions, also in the more labile H2O and NaHCO3 fractions. Based on results of sequential extraction of P-o and enzymatic hydrolysis, lability and bioavailability was in decreasing order as follows: H2O-P-o > NaHCO3-P-o > NaOH-P-o, and bioavailable P-o accounted for only 12.1-27.2% of total P-o in sediments. These results suggest that the biogeochemical cycle of bioavailable Po might play an important role in maintaining the eutrophic status of lakes.