The Spatial Distribution Of Nitrogen And Phosphorus In Surface Sediment And Their Influence Factors In The West River Network Of The Lake Taihu Basin

Nitrogen（N）and phosphorus（P）are the basic elements for biota in lake ecosystems.N and P have been demonstrated to be one of the main reasons for water eutrophication.Thus,they are key point that can be controlled to limit lake eutrophication.River sediments are an important accumulation pool of nutrients.Nutrients accumulated in river sediment could be one source of nutrients in water column under certain conditions,they could also be an important indicators to assess environmental pollution.Thus,it’s important to assess spatial distribution of sediment N and P,and the related factors that would affect their distributions.To do so,two main input rivers of west river network（West Tiaoxi and Yili-Taoge）of Lake Taihu basin were chosen as research objects,and water and sediment samples were collected from the main tributaries and main channels.All sample were determined the concentrations and forms of different N and P,and analyzed the spatial distribution and influence factors.The results showed that land utilization and hydrodynamic conditions could significantly affect the spatial distributions of N and P in surface sediments in both of our research regions.The concentrations of sediment total nitrogen（TN）in the West Tiaoxi and Yili-Taoge river systems ranged from 142.60 to 12597.68 mg·kg^-1,and total phosphorus（TP）ranged between 308.09 and 4328.57 mg·kg^-1,respectively.The concentrations of TN and TP in the sediments in West Tiaoxi river systems were higher than these in Yili-Taoge rivernet.In both regions sites near high density of population and industry area had higher concentrations of N and P than the other sites,which means N and P distributions were strongly influenced by discharges of domestic and industrial sewages.The spatial distributions of N and P are different between two research regions because of different hydrodynamic conditions.Ammonium nitrogen（NH₄⁺-N）was the main form of inorganic nitrogen（IN）in surface sediments in both river systems,and its concentration in the West Tiaoxi rivernet(mean 120.90 mg·kg^-1)were higher than in the Yili-Taoge rivernet(mean49.85 mg·kg^-1).However,the concentrations of nitrate nitrogen（NO₃^--N）were highest in Yili-Taoge river system with mean value of 13.95 mg·kg^-1.As the main form of IP in surface sediments,metal oxide bound phosphorus（Fe/Al-P）concentrations were lower in West Tiaoxi rivernet than in Yili-Taoge,with the mean concentrations of 192.57 and 278.59 mg·kg-1,respectively.The mean values of Fe/Al-P indicated a serious environmental contamination in both regions.Other IP forms in sediments of both river systems was Calcium bound phosphorus（Ca-P）>soluble reactive phosphorus（SR-P）>loosely sorbed phosphorus（NH₄Cl-P）.The concentration values of Ca-P and SR-P but NH₄Cl-P were higher in Yili-Taoge than in West Tiaoxi rivernet.The concentrations of different nitrogen forms in surface sediment were higher than N concentrations of overlying water body in both West Tiaoxi and Yili-Taoge river systems.In addition,spearman correlation analysis showed that there were significant correlations between different N and P forms in the surface sediments,and between surface sediments and overlying water columns.The concentrations of N and P in river network sediments reflected the pollution condition of the rivers,and the N and P accumulated in surface sediment would potentially release to the overlying water.