Characteristics of bioavailable organic phosphorus in sediment and its contribution to lake eutrophication in China

This study aims to establish the relative importance of sediment organic phosphorus (P_o) to the total P and the major classes of organic molecules that contribute to sediment P_o, determined by measuring their susceptibility to enzymatic hydrolysis, across a suite of lakes ranging from oligotrophic to eutrophic status. The results showed that P_o accounted for 21–60% of total P, and bioavailable P_o accounted for 9–34% of P_o in the sediments. The bioavailable P_o includes mainly labile (H₂O-P_o) and moderately labile (NaOH-P_o) P forms. For H₂O-P_o (accounting for only1.4% of P_o), 53% (average) was labile monoester P, 28% was diester P and 17% was phytate-like P. For NaOH-P_o (accounting for 9–33% of P_o), 32% was labile monoester P, 33% was phytate-like P and 18% was diester P. The composition of bioavailable P_o, determined by enzyme assays, was related to the lake nutrient levels, which implies that sediment bioavailable P_o could act as an effective indicator for lake eutrophic status. With the increase of lake nutrient levels, bioavailable P_o content and alkaline phosphatase activity in the sediment all increased, indicating that P_o represents an important and bioavailable source of P that increases with eutrophication, and could contribute to internal loading and resistance of eutrophic lakes to remediation. This implies that eutrophic lakes would maintain long-term eutrophic status and algal bloom phenomena even after the external input of P was controlled and the total P concentration of water has declined. Thus, in order to reduce the release risk of sediment P more efficiently and effectively, sediment P control technique should focus not only on reducing the total P and inorganic P, but should also pay close attention to the removal of bioavailable P_o. - Highlights: • Relationship between sediment P_o and lake nutrient levels. • Importance of sediments P_o and bioavailable P_o to the total P. • Composition of bioavailable P_o was related to the nutrient levels. • P_o represents an important and bioavailable source of P that increases with eutrophication. - The composition of bioavailable P_o in sediments was related to the lake nutrient levels and represents an important and bioavailable source of P that increases with eutrophication.