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

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 P-31 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 P-31 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. (C) 2018 Elsevier Ltd. All rights reserved.