Abstract: The adsorption-desorption between phosphorus and suspended sediment particles in rivers or lakes would influence the cycling process of water quality components. In this research, the calculation formulas for particulate phosphorus (PP) and dissolved phosphorus (DP) concentrations were deduced based on the classic Langmuir equation and the modified Langmuir equation, respectively. Furthermore, the experimental data and in-situ observed data of phosphorus and suspended sediment in Xiangxi River were used to verify the deduced formulas, and the calculated results were well consistent with the observed data. When suspended sediment concentration was low, the linear equation could work well, but when suspended sediment concentration was relatively high, the deduced formula needs be used, especially when adsorption and desorption coexisted, the formula deduced by modified Langmuir Equation needs be used. The research results could be applied for water quality and ecological modeling.

Key words: suspended sediment, particulate phosphorus, dissolved phosphorus, concentration, adsorption-desorption, Xiangxi River