Bioavailability and preservation of organic phosphorus in lake sediments: Insights from enzymatic hydrolysis and 31P nuclear magnetic resonance

Abstract Bioavailability and preservation of organic P (P o ) in the sediment profiles (DC-1 and DC-2) from Lake Dianchi, a eutrophic lake in China, were investigated by a combination of enzymatic hydrolysis and solution 31 P nuclear magnetic resonance (NMR) spectroscopy. Results showed that large of P o could be extracted by NaOH-EDTA (NaOH-EDTA P o ), with little P o in residues after extraction with NaOH-EDTA. Bioavailability and preservation of NaOH-EDTA P o provide key information for biogeochemical cycling of P o in sediments. The details of P species and their bioavailability in NaOH-EDTA P o showed that 54.8–70.4% in DC-1 and 54.6–100% in DC-2, measured by 31 P NMR, could be hydrolyzed by the phosphatase. Whereas, some proportion of NaOH-EDTA P o could not be hydrolyzed by the phosphatase, and decreased with sediment depth. Interaction between P o and other organic matter (e.g., humic acids) is likely an important factor for preservation of these P o in the sediment profiles. Simulation experiments of hydrolysis of model P o compounds adsorbed by minerals, such as goethite and montmorillonite, further indicated that adsorption to minerals protected some P o , especially phytate-like P, from enzymatic hydrolysis, thus preserving these forms of P o in sediments. Interactions of P o with organic matter and minerals in the sediments are two important factors determining biogeochemical cycling of P o in lakes. Intervention to break the cycle of Fe P and bioavailable P o (e.g., labile monoester P) in the history of eutrophication is important way to control algal blooming.