Response of sediment organic phosphorus composition to lake trophic status in China

Organic phosphorus (P_o) constitutes the most important fraction of P in lake sediments, and the compositional properties of P_o affect its behavior in lake ecosystems. In this study, ³¹P NMR, FT-IR spectroscopy, and UV-visible absorbance spectroscopy were combined to identify the dynamic composition of sediment P_o across two sets of lakes in China ranging from oligotrophic to eutrophic, and their possible effects on lake eutrophication were evaluated. The results showed that sediment P_o content (accounting for 24-75% of TP) was positively correlated with trophic status in both Eastern Plain and Yun-Gui Plateau lakes of China, and the linear relationship was more stable compared to total P (TP), implying that sediment P_o may be a superior indicator of trophic status than TP. The P_o component, phosphonate accounted for only 0.4% or less of P_o, while the monoester P and diester P, accounted for 2-24% and 0.5-5% of P_o, respectively, and were the main factors causing P_o to increase with the increasing trophic status. The factors were closely related to the enhanced organic sewage load and intensification of contemporary sedimentation of phytoplankton. As trophic status increased, sediment P_o might integrate into larger amounts of aromatic substances and functional groups, which could enhance the stability of P_o in sediments. Furthermore, sediments from lakes with higher trophic status exhibited a higher degree of humification and molecular weights, which impart resistance to biodegradation, and therefore, reduced the risk of sediment P_o release. However, the massive accumulation of bioavailable P_o (monoester and diester P) allows possible degradation, supporting algal growth and maintains eutrophic status because there is abundant alkaline phosphatase in eutrophic lakes. Thus, to control lake eutrophication more effectively, targeted actions are urgently required to reduce the accumulation and degradation of P_o in lake sediment.