The potential role of sediment organic phosphorus in algal growth in a low nutrient lake

The role of sediment–bound organic phosphorus (Pₒ) as an additional nutrient source is a component of internal P budgets in lake system that is usually neglected. Here we examined the relative importance of sediment Pₒ to internal P load and the role of bioavailable Pₒ in algal growth in Lake Erhai, China. Lake Erhai sediment extractable Pₒ accounted for 11–43% (27% average) of extractable total P, and bioavailable Pₒ accounted for 21–66% (40%) of Pₒ. The massive storage of bioavailable Pₒ represents an important form of available P, essential to internal loads. The bioavailable Pₒ includes mainnly labile monoester P and diester P was identified in the sequential extractions by H₂O, NaHCO₃, NaOH, and HCl. 40% of H₂O−Pₒ, 39% of NaHCO₃−Pₒ, 43% of NaOH−Pₒ, and 56% of HCl−Pₒ can be hydrolyzed to labile monoester and diester P, suggesting that the bioavailability of Pₒ fractions was in decreasing order as follows: HCl−Pₒ > NaOH−Pₒ > H₂O−Pₒ > NaHCO₃−Pₒ. It is implied that traditional sequential fractionation of Pₒ might overestimate the availability of labile Pₒ in sediments. Furthermore, analysis of the environmental processes of bioavailable Pₒ showed that the stabler structure of dissloved organic matter (DOM) alleviated the degradation and release of diester P, abundant alkaline phosphatase due to higher algal biomass promoted the degradation of diester P. The stability of DOM structure and the degradation of diester P might responsible for the spatial differences of labile monoester P. The biogeochemical cycle of bioavailable Pₒ replenishs available P pools in overlying water and further facilitate algal growth during the algal blooms. Therefore, to control the algal blooms in Lake Erhai, an effective action is urgently required to reduce the accumulation of Pₒ in sediments and interrupt the supply cycle of bioavailable Pₒ to algal growth.