Endogenous phosphorus release risks and functional pathway responses: a comparative study on plateau and plain representative lakes.

The regional characteristics of plateau and plain lakes are critical factors influencing endogenous phosphorus (P) release from sediments. This study focuses on two representative lakes: a plateau lake (YamdrokTso Lake) and a plain lake (Taihu Lake), to investigate differences in P release characteristics, risks, and fraction contributions in sediments between these two systems. The results showed that the sediments from the plateau lake (Sau) exhibited a higher P sorption capacity (2.24 mg g-1), with sediments in all regions acting as P sinks. In contrast, most sediments from the plain lake (Sin) functioned as P sources, with a few regions acting as P sinks. The mean value of P release risk index (ERI) of Sau was 30.10%, while the maximum ERI of Sin reached 86.80%, indicating lower P release risk in Sau and higher risk in Sin. Further analysis of P form contributions to overlying water across long-time (bottom sediment) and short-time (surface sediment) gradients revealed that in Sin, all P fractions in both bottom and surface sediments significantly contributed to P concentration in overlying water, NaOH-P being the dominant contributor. In Sau, organic P (OP) and HCl-P from surface sediment contributed moderately to P concentrations in overlying water, while HCl-P emerged as the primary contributor over the long-time gradient. Function prediction results showed that the activities of key pathways related to P activation, such as "inositol phosphate metabolism" and "phospholipase D signaling pathway", were suppressed in plateau sediments yet strongly enriched in plain lake sediments. This study links sediment P source-sink behaviors to microbial functional traits across plateau and plain lakes, providing theoretical support for regional endogenous lake pollution control.