Phosphorus adsorption and release characteristics of surface sediments in Dianchi Lake, China

Phosphorus adsorption and release characteristics of surface sediments from Dianchi Lake were investigated through indoor simulation experiments. Kinetics and thermodynamics of adsorption and release of phosphorus in sediments were studied, and the influence of different phosphorus fractions on adsorption and release was analysed. Results show that the total phosphorus content in the sediments ranged from 843.96 to 8144.44 mg kg⁻¹, which was 2–8 times as much as those in other lakes in China (e.g. Erhai Lake and Taihu Lake). The average values of different phosphorus forms in the sediment samples were ranked in the order of organic P (OP), calcium-bound P (Ca-P), metal oxide-bound P (Al-P), residual P (Res-P), Fe-bound P (Fe-P) and weakly absorbed P(NH₄Cl-P). Compared with the case of other lakes in China, the sedimentary phosphorus adsorption capacity of Dianchi Lake was at a higher level, but its maximal release rate and release capacity were low, indicating a relatively low release risk. By comparing the equilibrium phosphate concentration in the sediments and the soluble reactive phosphorus in the overlying water, the risks of phosphorus release from sediments in Caohai, Lake Central and Southern Waihai were found to be relatively low in the short term, but were high in Northern Waihai. The release behaviour of sedimentary phosphorus in Dianchi Lake was mainly determined by NH₄Cl-P, Fe-P and Al-P, among which NH₄Cl-P and Fe-P served a greater function. Therefore, the contents of different fractions of phosphorus and their distribution characterization should be considered when characterizing the adsorption and release status of lake sedimentary phosphorus.