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, P-31 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. (C) 2018 Elsevier B.V. All rights reserved.