Organic P poses high releasing risk from sediments in lake with long history of eutrophication and algal blooms

Organic phosphorus (P_o) is an important component of sediment P in eutrophic lakes and may play a crucial role in maintaining eutrophication, but this is often overlooked. This study analyzed the contents, various chemical forms of P_o in surface sediments collected from the Dianchi Lake in China, with long history of eutrophication and algal blooms. The simultaneous release of P_o and inorganic P (P_i) from the collected sediments under varied pH, temperatures, and oscillation simulation conditions was also investigated. The results showed that: (1) P_o accounts for 42.3 %–49.3 % of the total P (P_t), and contributs almost equally to P_i toward sediment P load. Organic residues such as endophytic algae are likely the main source of P_o in sediments; (2) P_o in sediments was primarily in the forms of NaHCO₃-P_o, HCl-P_o, and residual-P_o (Res-P_o) (over 90 % of P_o). The labile P_o (LP_o) and moderately labile P_o (MLP_o) components accounted for about 60 % of total P_o, indicating its significant potential for participation in the P biogeochemical cycles; (3) The simultaneous release of P_o and P_i from the sediments was significantly affected by pH, temperature, and oscillation simulation conditions. Especially the simultaneous release of P_o relative to P_i becomes consistently higher and shows a significant positive correlation with the release of P_t (P < 0.01), indicating P_o poses high releasing risk from sediments in the Dianchi Lake. Our findings suggest that against the backdrop of increasing eutrophication worldwide, the control of internal P_o pollution in closed water systems (e.g., lake) is urgently needed.