To reveal the characteristics of organic phosphorus release from lake sediments and its potential impact on water quality, six lake sediments from Yunnan Plateau and the middle and lower reaches of the Yangtze River in China were selected. We studied the differences in the kinetics of dissolved organic phosphorus (DOP) and dissolved inorganic phosphorus (SRP) release from sediments. The effects of organic phosphorus morphology and dissolved organic matter (DOM) characteristics on sediment phosphorus release were investigated, and the water quality risks of sediment DOP release were discussed. The results showed that:① the release kinetics of sediment DOP and SRP were similar; both followed the second-order kinetic model, starting with a rapid release phase, followed by a slow release, and the release curve gradually leveled off and reached the maximum release. ② The release of organic phosphorus was related to organophosphorus morphology and organic matter. Active organic phosphorus (LOP) and medium active organic phosphorus (MLOP) were the DOP forms mainly released into the overlying water during the rapid release phase. The proportion of LOP and MLOP to total organic phosphorus (DTP) decreased in the late release stage, whereas the proportion of non-active organic phosphorus (NLOP) increased; further, the degree of humification and aromaticity of organic matter gradually increased with phosphorus release, and its activity decreased, resulting in a slower release rate at the later stage. ③ Compared with that of SRP, the risk of DOP release was higher, accounting for 47%-77% of the total amount of DTP. It was also found that the higher the nutrient level of the lake, the greater the release of DOP and the higher the water quality risk. Therefore, not only the release of inorganic phosphorus but also that of organic phosphorus should be of concern in the process of phosphorus release from lake sediments to prevent the underestimation of phosphorus release and water quality risk.
Keywords: organic phosphorus; phosphorous forms; release kinetics; sediment; water quality risks.