Phosphorus release in response to pH variation in the lake sedimentswith different ratios of iron-bound P to calcium-bound P

Phosphorus released from the sediment may render lakes eutrophic under appropriate pH and redox conditions. Phosphorus speciation in lake sediments was investigated by a Standard Measurements and Testing (SMT) protocol in three shallow lakes: Taihu Lake, Chaohu Lake and Longganhu Lake in the middle and lower reaches of the Yangtze River in China. Twelve lake sediment samples with different ratios of iron-bound phosphorus (Fe-P) content to calcium-bound phosphorus (Ca-P) content were collected and exposed to various pH conditions. These sediment samples showed different patterns of P release responding to pH variations under an oxic condition. The sediments with Fe-P/Ca-P ratios less than 0.5 released more phosphorus under acidic conditions, while the sediments of higher Fe-P/Ca-P ratios released more phosphorus under alkaline conditions. The various patterns of phosphorus release from these lake sediments are dependent on the concentrations of the reactive Al and Fe forms and organic matter, which mainly contribute to the different Fe-P/Ca-P ratios. Therefore, a ratio of Fe-P content to Ca-P content in the sediment might be regarded as a simple index for the risk assessment of acidity-related or alkalinity-related release of phosphorus.