Study On The Distribution Of Phosphorus Fractionations And The Flux From Sediments In Erhai Lake

The study on the behavior of phosphate in the sediment-water interface is of great significance to illustrate the mechanism of Lake eutrophication, of which the study on the speciation, the adsorption-desorption characteristics and the endogenous emission flux of phosphate in the sediments further reveal the mechanisms of phosphate transport and transfer in sediment-water interface and provide favorable supporting data for the estimate of the release risk of phosphate in the sediments. Erhai Lake is currently in the infancy of eutrophication development; however, the generally high contents of organic matter, total nitrogen and total phosphate in the sediments from Erhai Lake pose a high risk to phosphate release. Thus the study on the speciation, the adsorption-desorption characteristics and the endogenous emission flux of phosphate in the sediments from Erhai Lake which are selected as research object are analyzed, meanwhile, try to provide scientific basis for the treatment of eutrophication in Erhai LakeThe conclusions based on above analysis are drawn:(1) The TP contents in sediments of study area ranged from 418.7-1750.6 mg/kg, with the mean value was 921.1±233.1mg/kg. The TP content in Erhai Lake sediments of the northern, central lake and Haidong bay was higher than other areas. The TP content in west bank sediments was higher than east bank. The rank order of phosphorus fractionation in sediments of Erhai Lake was HCl-P(Apatite and CaCO3 bound P)>Res-P(Organic refractory P),NaOH-rp(Metallic oxide bound P)>BD-P (Reductant soluble P)>NaOH-nrp(Organically bound P)> NH4Cl-P(Loosely bound P). The BD-P, NaOH-rp, HCl-P and Res-P contents in Erhai Lake sediments were significantly positively correlated with TP (p<0.01). These phosphorus fractionations were the major phosphorus composition in sediments. The BAP(Bioavailable P) content was significantly positively correlated with BD-P, NaOH-rp and TP (p<0.001). The high BAP content in sediments showed high internal phosphorus loading and release risk.(2) The process of phosphorus release kinetics of the surface sediments in Erhai Lake were divided into the rapid release stage, the slow release stage and the release of balance stage. With the large variances of release phosphorus rates in diffident periods, the release rates was maximum in 0-0.5h that ranged from 5.38～20.47 mg/(kg h). After 15h later, the release rates was approximately 0.0097～0.0856 mg/(kg h). The phosphorus release rate in the initial stage was about 240 times to the final. The Elovich equation was well used to describe the kinetics of phosphorus release process (p<0.001).(3) The phosphate releasing flux of the sediments from different layers declined gradually from north to south.The phosphate releasing flux of the sediments in the top surface of Erhai Lake was significantly lower than that in the depth away from the surface. The variation of the phosphate release rates in four sampling sites that appeared to ascend beginning with a relatively low release rate on the surface and followed by a decrease gradually to plateau with depth were basically the same. As a whole, the relation of phosphate releasing flux of the sediments from Erhai Lake was Ea> Eb> Ed> Ec.(4) The process of phosphate adsorption kinetics of the surface sediments in Erhai Lake were divided into the rapid adsorption stage and the slow adsorption stage, which mainly occurred in the first 0.5 h and in 0.5～5h respectively. The phosphate adsorption of all the sediments reached equilibrium within 5 h. The phosphate adsorption capacity (Qmax,904.60～1420.34 mg/kg) and maximum buffer capacity (MBC,477.33～2300.95 L/kg) of the sediments in different sites of the east bank were significantly higher than those in the west bank; but the comparison of adsorption-desorption equilibrium concentrations (EPC0,0.015～0.068 mg/L) in different sites showed an opposite trend. The total calcium and total organic matter contents of the sediments were significantly positively correlated with Qmax and the maximum adsorption rate (Vmax), but were significantly negatively correlated with EPC0. The phosphate adsorption parameters of the surface sediments Qmax and Vmax were significantly higher, while EPC0 was lower, than the corresponding parameters of the shallow lakes in the middle and lower reaches of Yangtze River catchment. Therefore, the high contents of total calcium and total organic matter in sediments might account for the high risk but low amount of phosphate release in the sediments of Erhai Lake.