Internal Phosphorus Loading In Lake Dianchi And Synthetic Material For Controlling Its Sediment-water Interface Flux

Eutrophation is a serious problem that has attracted worldwide attention fromscientists and government agencies. Internal P-loading, which is negligible for therestoration of shallow lakes, may delay the recovery of lakes following the reduction ofexternal P-loading sources. Determine and quantification the internal P-loading is essentialfor lake internal loading management. A novel sediment-water interface phosphorus fluxcontrol material (PFCM) was synthesized by use of the sediments of Lake Dianchi and itslocal red soil. The main results are as follows:1) The average content of total phosphorus in the surface sediment of Lake Dianchiwas around2184.39±579.09mg/kg, and there was5.2×104t phosphorus in the top15cmsediments. Calcium bound P (HCl-P) was the main fraction of sediment phosphorus, and itaccounted for40.63%of TP. The potential mobile phosphorus represented5.89~23.99%ofTP, among which，redox sensitive bound P (BD-P),metal oxide bound P (NaOH-rP) andorganic P (NaOH-nrP) was6.14%,20.45%and5.36%of TP respectively. In the surfacesediments, the rank order of P-fractions was HCl-P>NaOH-rP> NaOH-nrP>Res-P>BD-P.2) Diffusive flux of soluble reactive phosphorus(SRP) across the sediment-waterinterface (SWI) of Lake Dianchi was-0.296~0.489mg/(m2·d), and the dissolved organicphosphorus release flux was-1.605~3.644mg/(m2·d). Sediment was a significant source ofphosphorus in the annual budget for Lake Dianchi. Diffusive flux of phosphorus from LakeDianchi sediments contributes~9.39%of the annual P load, and the diffusive DOP fluxaccounted for97.07%of the internal P-loading. The results indicated that the internalP-loading of Lake Dianchi was serious.3) The bath experiments showed that the adsorption kinetics of phosphate insediments of Lake Dianchi was divided into three processes, namely fast adsorption, slowadsorption and equilibrium stage. The adsorption equilibrium time was24h. TheP-bounding capacity of both sediment and local red soil can be increased by calcination.The optimum calcination temperature was600℃.4) The addition of local red soil clay can reduce the equilibrium phosphorusconcentration of adsorption materials, the ideal mass ratio of sediment and mixture50%~90%. After the modification of polyaluminium chloride and corncob the adsorptioncapacity of phosphate was increased to3times of the origin material. 5) The adsorption process of Phosphorus by PFCM fits the Langmuir non-lineradsorption model greatly. Optimal operating conditions such as temperature, pH valuehave been determined. The phosphorus adsorption capacity of PFCM increased with theincreasing the calcination temperature, and the adsorption process was endothermic andthe reaction was spontaneous. The removal rate of phosphate decreased with the increaseof the pH in the solution.6) The laboratory incubation tests suggestted that the PFCM can enhance the redoxpotential (Eh) and dissolved oxygen (DO) in surface sediment, and it can be used forsediment–water interface phosphorus flux control. The dosage of PFCM applied in LakeDianchi was0.23~9.71kg/m2.