Occurrence and distribution of phosphorus fractions in sediments of Liangzi Lake under typical hydrodynamic conditions.

Understanding the transformation and chronological accumulation of phosphorus (P) forms under typical hydrodynamic conditions of a lake is important for clarifying the process of lake evolution and eutrophication. The occurrence and distribution of sediment P fractions (total, TP; inorganic, IP; and organic, OP), phytate content, and phytase activity at different profile depths (0-8 m) and parent material ages (0.8-11 ka BP) were examined at different ecological locations (inlet, outlet, and center) of the freshwater Liangzi Lake in Hubei Province, China. Sediment P-forms at locations of different hydrodynamic conditions increased from the inlet to the outlet. IP constituted ∼40-71% of TP, whereas the OP content was generally lower in the sediment. The two forms of IP extracted by HCl and NaOH varied quantitatively with depth and location: HCl-P ≈ NaOH-P (above 0.8 m) or HCl-P > NaOH-P (below 0.8 m) at the inlet; HCl-P > NaOH-P (above 0.8 m) and HCl-P ≈ NaOH-P (below 0.8 m) at the outlet; and HCl-P < NaOH-P at the center of the lake. Compared with labile and moderately resistant OP, moderately labile OP exhibited substantial quantitative changes and occurred at high levels. The variation trend in the phytate content coincided with that of TP, whereas phytase activity varied inversely with location. Low levels of P forms occurred in the sediment below 4.5 m and before 8.6 ka BP, consistent with the oligotrophic period of the lake. During 2-4 ka BP, the P forms first increased rapidly and then stabilized thereafter. From that time period until modern times, TP and phytate increased, whereas IP and OP decreased significantly. The results indicate that the hydrodynamic conditions of the water bodies and the sediments of different ages strongly influenced the occurrence and distribution of sediment P forms, and the sediment TP and phytate contents would be candidate indices to reflect the P input and eutrophication history of freshwater lakes.