Dynamics of phosphorus composition in suspended particulate matter from a turbid eutrophic shallow lake (Lake Chaohu, China): Implications for phosphorus cycling and management.

Particulate phosphorus (P) dominates the total P (TP) content in lacustrine water columns and is a primary source of dissolved P in turbid eutrophic shallow lakes. However, the spatiotemporal variability of P compositions in suspended particulate matter (SPM) remains poorly understood. In this study, we applied chemical extraction and solution 31P nuclear magnetic resonance (31P NMR) to assess the seasonal variations of SPM P compositions from a shallow turbid lake (Lake Chaohu, China) and its main river tributaries. P fractionation analysis indicated that mobile P (the sum of labile-P, iron-bound P, and organic P) accounted for >60% of the TP in SPM and showed high spatiotemporal variability throughout the year-long field investigation. In most seasons, riverine SPM (in urban rivers or rivers with high flow) contained a higher mobile P content than that of the lake and was therefore a dominant source of lacustrine mobile particulate P. Solution 31P NMR identified five types of P compounds in SPM, with highest contributions from orthophosphate. Organic P components and concentrations showed high seasonal variability, and elevated p values occurred during the summer algal bloom. The correlation analysis between organic and inorganic P fractions inferred the possible degradation of organic P into reactive inorganic components of SPM. Consequently, biological or chemical processes would further transform the labile inorganic P into soluble reactive phosphorus, which is readily utilized by lacustrine algae. Our results suggest that the labile forms of P in SPM were highly dynamic and significantly contributed to the eutrophication of the turbid shallow lake.