Phosphorus sink-source function of a lakeside surface flow wetland
表流湖滨湿地磷素汇-源功能研究

Laboratory experiments under static conditions were performed on the sediment of a lakeside wetland,the Maliaohe river wetland of Fuxianhu lake,to investigate the Equilibrium Phosphorus Concentration(EPC0) of the sediment-water interface.The EPC0 is used as an indicator of the source or sink function of the sediment for soluble reactive phosphorus(SRP).In-situ observations of SRP and flow rate were also carried out for the Maliaohe river wetland to verify the laboratory experiments.The field observations showed that the function of the sediment as a source or sink for SRP depends mainly on the flow rate and the phosphorus concentration of the wetland inflow.During storms,the SRP concentration of the effluent is lower than that of the influent due to dilution by rainwater.When the flow rate is low,the SRP concentration of the influent plays an important role in determining the function of the sediment.When the SRP concentration of the influent is greater than the EPC0,the sediment functions as a sink for phosphorus,but otherwise it functions as a source.A simple mathematical model was used to estimate the interaction between the sediment and the overlying water column and the SRP flux across the sediment-water interface.In the model,the sediment-water interface was assumed to be the top 10 cm of the sediment,and processes of SRP adsorption and release were assumed to occur within this layer.The model showed that the rates of adsorption and release of SRP by the sediment were quite high when the water and the sediment were in a complete mixing condition.A large proportion of the SRP flux across the interface occurs within the first one hour.The adsorption or release of SRP by the sediment is mainly subject to the EPC0 and the concentration gradient of the SRP of the influent.