Phosphorus release from the sediment of a drinking water reservoir under the influence of seasonal hypoxia

Seasonal sediment internal phosphorus (P) release may cause water eutrophication and impair water quality in drinking water reservoir. During a year-long field investigation, the effects of the microenvironment on the release of internal phosphorus were meticulously analyzed using high-resolution peepers technique and microelectrode system. The release mechanisms of P fractions from the reservoir sediments were also explored. The results showed that seasonal fluctuations in temperature, dissolved oxygen, redox potential, and pH at the sediment-water interface impacted the release of P fractions from the studied reservoir sediment. Higher diffusive fluxes of soluble reactive PO43− and Fe2+ across the sediment-water interface (SWI) were observed in the warmer season and were approximately 14.5 times and 16.5 times than those in winter, respectively. Driven by seasonal hypoxia, the reservoir sediment functioned as a P sink in winter and became a P source in summer and autumn. The reduction of Fe-bound P and mineralization of organic P were the primary mechanisms driving sediment P release, which explains the increased P flux in the warmer season and lower P flux in winter. The findings indicated that elevated temperatures and anaerobic conditions were conducive to the activation of P in sediments, whereas lower temperatures and aerobic conditions promoted the immobilization of P. This study provided new insights into seasonal P cycling in reservoirs that can contribute to the formulation of targeted reservoir management strategies.