The Phosphorus Distribution And Transformation In Water And Sediment Of Qingcaosha Reservoir

The Qingcaosha (QCS) reservoir is locted on the Yangtze estuary, which is one of importantdrinking water resources in Shanghai. The Yangtze estuary is well-watered and good water quality,and also is deposition of suspended matter on the sediment. However, saltwater intrusion into theYangtze Estuary is mainly affected by the fresh water discharge from the Yangtze River. Thecurrent of water from the Yangtze can be slow after entering QCS reservoir. The pollutant bindingon the matter was removed with the process of deposition, because of the long retaining time. Theretention is important for the purification of reservoir and the growth of algae, even though theeutrophication. The phosphorus is a major nutrient for aquatic ecology and its excess supply leadsto eutrophication. The aims of this study were to study the content of P both in the water body andsediment; to investigate the characteristics of sedimentary P fraction in the QCS reservoir; toexplore how the concentration of P in the overlying water affected sediment behavior in acting asa P source or sink, and to analyze the relationship between the P fractions and the capacity of Padsorption-release. The phosphate sorption-release characteristics of the sediment from coastalestuaries, oceans and lakes have been extensively studied. However, no study has been reportedregarding the QCS reservoir sediment, and little is known about this area’s P fractions ofsediment.The result showed, the turbidity reduced and the transparent induced from up to downstreamin the QCS reservoir. The concentration of nitrogen, phosphorus and metal was higher in the inletthan that in outlet of reservoir. The removal rate of TP, SRP and PRP from the upstream to thedownstream of the reservoir was approximately69.28,80.38and41.24%respectively. Theremoval rate of TN, NO-+3-N and NH4-N was43.44,45.71and40%. The removal rate of Ni, As,Mn, Mo, Fe, Co, Cr, Pb was25,41,38,13,79,42,47,23%. The deposition of the pollutantattached to the suspended matter on the sediment in the water was easy due to gravity. This is themajor reason why pollutant concentration in the reservoir decreased hence improving the waterquality of the reservoir.There are five phosphorus fraction in the sediment of QCS reservoir: TP，IP，HCl-P，NaOH-Pand OP. The calcium binding phosphorus fraction in the sediment was major in the totalphosphorus. Compared with the TP content in the world, sedimentary TP in QCS reservoir rankedin the middle level. The low percentage of NaOH-P and OP in the sediment showed that thepollution came from nature. The high percentage of HCl-P showed that the phosphorus sinked tothe HCl-P, which have a relationship with active calcium. The phosphorus concentration can bedeclined by the binding calcium to reduce the risk of eutrophication.For the adsorption and release of process in the sediment, the modified Langmiur was used.The result showed that the adsoption capacity Qmaxwas39.84mg/kg, EPC0ranging from0.067to 0.242mg/L, NAP ranging from1.89to5.66mg/kg in the sediment. The adsorption of P dependedon the physics and chemical properties. In this study, the EPC0values for all sites were higher thanthe SRP concentration values in the corresponding water column sites. This indicates that thesediment as a source would release P into the overlying water in all sites. The relationship betweenthe EPC0and IP indicated that the inorganic phosphorus fraction was the major resource of releasefrom sediment. The relationship between the NAP and HCl-P indicated that the phosphorusadsorbed the calcium.The environmental factors effect on the phosphorus release. The result showed the temperature,pH, the concentration of calcium, Cl-and SO2-4effected on the P release from sediment. Theincreasing temperature promoted the P release from sediment. The alkaline promoted theformation of calcium binding phosphorus. During Ca treatment, the adsorption capacity Qmaxincreased, and the capacity of P release reduced. The effect of chloride on sediment could beattributed to the amount of fine-size particle accumulation on the surface sediment. At the sametime, the SO42-from seawater intrustion enhanced P release from sediment.The QCS reservoir is one of the world’s largest multi-sand reservoirs, where the suspendedmatter of the Yangtze is deposited. It is helpful for phosphorus purification. The adsorption andrelease was occurred in the interface of water and sediment, and it is the risk of phosphorusincreasing. To control the eutrophication, the phosphorus should not ingored in the drinking waterresource.