Phosphorus Forms And Release In Sediments Of Typical Reservoirs For Drinking Water Supply In Guangdong Province

Twenty-eight reservoirs for drinking water supply in Guangdong Province were investigated to know internal loadings of phosphorus.By measuring phosphorus species in sediments and phosphorus release rate in situ,this thesis analyzed the vertical profiles of phosphorus and the relationship between the phosphorus species and to phosphorus concentration in water columns, discussed existing strategies for effective reduction of internal loading.The contents of TP(total phosphorus) in sediments ranged from 0.225 mg/g to 3.02 mg/g,The content of TP in Tongsha reservoir was 3.02 mg/g,which was highest in all of the reservoirs we investigated.The P content averaged over watershed was 0.458—0.911 mg/g in six watersheds,and the highest contents of TP was 0.911 mg/g and appeared in the Pearl River Delta.The data show that the external pollution, reservoir volume,hydraulic retention time and basin morphology are the key elements regulating the phosphorus forms and release rate.The contents of TP and IP(inorganic phosphorus),OP(organic phosphorus),NaOH-P and HCl-P in the reservoirs located at coastal areas which were usually accepted more loading than those the other areas.The contents of TP and IP,OP,NaOH-P and HCl-P in sediments fro the small sized reservoirs are generally higher than the middle and large ones. Usually,the longer the hydraulic retention time of reservoirs is,the higher the contents of TP in sediments(longer than 100 days).The main species were inorganic phosphorus in the most of reservoirs;NaOH-P was the main component in the inorganic phosphorus,due to the Fe and Al rich soils that is common in South China.OP can be dominant in some of large and middle sized reservoirs with a low external loading.The contents of TP and other species increase vertically from the bottom to surface sediment,indicating an increase in the external loading.However,the reverse or constant profiles can be observed in oligo or meso-trophic reservoirs.The PO₄-P releases rate in sediments show a relationship(r＞0.80,p＜0.05) with TP concentration in water bodies,the relationship means that the main source of TP concentration in water column is directly or indirectly caused by algae using PO₄-P,and the PO₄-P is mainly released by the NaOH-P and OP.As fish enclosure fish culture and duck culture are the common human activity causing the direct internal loading,it has to be removed or limited out of the reservoirs for non drinking water supply.In comparison to natural lakes,an outlet mode for internal loading management needs to be developed.