The Phosohorus Adsorption-desorption Equlibirum And Regulation Mechanism Between Sediment Particles And Water In Shallow Lakes

In shallow lakes,sediment P（P）is the main source of P available to cyanobacteria in high temperature season,and contributes significantly to the peak of P concentration in water.In the process of cyanobacteria proliferation,p H increased,resulting in the release of a large amount of P in surface sediments,forming a"pumping"effect,which continued to support the growth of cyanobacteria and led to the increase of P concentration in water.Therefore,it is very important to clarify the balance mechanism of sediment-water phosphorus and quantify the response relationship between them,which can provide a theoretical basis for scientific evaluation of the contribution of sediment phosphorus pollution load to water phosphorus.Based on this,this paper carries out relevant research.In this study,Chaohu Lake and Taihu Lake,two eutrophic shallow lakes,were selected as representatives to collect surface sediments.According to the mechanism of algae pumping P,the response of sediment particles to P pollution concentration,particulate concentration and p H was studied.The main research results are as follows:（1）The total phosphorus（Ext-TP）concentration of the samples collected from Taihu Lake and Chaohu Lake ranges from 300 to 1800 mg kg^-1,weakly adsorbed phosphorus（Ex-P）ranges from 0 to 12 mg kg^-1,and iron-bound phosphorus（Fe-bound P,Fe-P）ranges from 50 to 550 mg kg^-1.Aluminum bound P（Al-bound P,Al-P）ranges from 50 to 700 mg kg^-1,calcium bound P（Cabound P,Ca-P）ranges from 70 to 200 mg kg^-1,and residue phosphorus（Res-P）ranges from 25 to 60 mg kg^-1.Wateractivated bed P on the lake by Fe/Al oxide-activated P was reduced from the upper reaches to the lower reaches by 100to 700 mg kg^-1.（2）For samples with different P pollution levels,different concentrations of particulate matter were set and the adsorb-desorption experiments were carried out under different pH conditions.And Logistic empirical equation of the response of P equilibrium concentration（C_e）to P load（C_m）and p H of Sediment Water Interface（SWI）in the equilibrium system is put forward as follows:C_e（pH）（28）C_m/^{[1（10）e-k（p H-p H1/2）]}.The concentration of C_ewas 0.001～0.771 mg L^-1,C_mwas 0.008～0.786 mg L^-1,k was 1.9～2.5p H^-1.The normalization result showed that Fe/Al-P was the main source of the release of p H activated P.The linear equation was:C_m（28）0.99*[Fe/Al（hydr）oxide-adsorbedP].（3）Further select three representative iron oxides ferrihydrite,goethite and hematite,and carry out adsorption P balance experiments under different P loads.It shows that the P balance in Fe mineral-water body and sediment-water body responds to P load and p H in the same way.（4）Based on the theory of surface complexation and the geochemical simulation software（Visual MINTEQ 3.1）,a two-phase distribution model of sediment particle-water P in shallow lake was constructed to further explain the balance and regulation mechanism of sediment particle-water P in shallow lake:The equilibrium concentration of P in sediment-water increases with the increase of Fe/Al-P concentration,particulate concentration,and p H.On this basis,a conceptual model of P equilibrium between sediment and water body in shallow lake is proposed,that is,the P equilibrium concentration of sediment in shallow lake depends on P load of interface layer and p H value of water body.The research methods and results are of great significance for analyzing the change of phosphorus concentration in shallow lakes and indicating the change of phosphorus pollution in sediments.