Study On The Characteristics Of Sediment Phosphorus Fraction After Normal Storage In The Three Gorges Reservoir

The impoundment of the Three Gorges Reservoir（TGR）has impact on the water environment and sediment transport characteristics of TGR.The transformation of phosphorus in sediments and water is in urgent need to study.Based on the hydrological characteristics and the sedimentation characteristics of the TGR,sediment sample were collected from Chongqing to Maoping,analyzed the organic matter（LOI）,median diameter(d₅₀)and mineral composition in sediments,determine total phosphorus（TP）and phosphorus fractions in sediments,and explore the correlation between the phosphorus fraction and the physical and chemical properties of the sediment,the effect of impoundment on the bioavailable phosphorus,TP,phosphorus fractions of sediments,and the impact of impoundments on the accumulation and bioavailability of sediment phosphorus;The contribution rate of phosphorus release from columnar sediments was calculated to assess the release potential of phosphorus fractions;the characteristics of sedimentation physicochemical properties,total phosphorus and various phosphorus fractions were analyzed during different water storage periods,revealing that the reservoir impounds effect on total phosphorus and phosphorus fractions in sediments.The main conclusions obtained are as follows:1)The organic matter content of sediments in the mainstream of the Three Gorges Reservoir ranges from 7.79 to 55.63 g·kg^-1.The main minerals are chlorite,illite,and quartz.The surface sediments of the main stream consist mainly of clay silt and columnar sediments.The sediment organic matter in the mainstream of the TGR is dominated by terrestrial input.Compared with the earlier years,the sediment particle size has shown a trend of refinement.LOI and d₅₀ have no obvious trend along the vertical direction.2)The TP content of sediments in the mainstream of the TGR surpass the background value of the total soil phosphorus content in the local area and there is a certain risk of ecological pollution.In addition,the vertical distribution of total phosphorus changed little and did not show surface enrichment.3)The contents of Fe-P,Al-P and Ex-P in the sediments of the TGR are relatively low,and the contents of Oc-P and Ca-P are relatively high.The contents of Al-P,Ex-P,Bio-P in sediment had close relationships with particle size and LOI.The sediment Bio-P is only2%～8%of total phosphorus,and its ability to participate in the overlying water phosphorus cycle is weak.In general,there was no significant change in the vertical distribution of the various forms of phosphorus.The contents of Ex-P,Al-P and Fe-P in the bottom 16-20cm were relatively stable.At the same depth,the content and relative content of Bio-P in different sections from Yunyang to Zigui show a trend of increasing along the range,and the relative content of Bio-P is 2.78～7.05%,and the risk of endogenous release is less.The content of IP in the sediments of the TGR increased significantly after a complete water storage period,and the Fe/Al-P content decreased significantly.4)With the reduction of sediment and the gradual refinement of sediment particles in the TGR,phosphorus may gradually accumulate in some of the wide valley sections of the TGR;Re-suspension of muddy mud will affect the bioavailability of phosphorus in sediments.