Spatial Variations of Nitrogen,Phosphorus and Heavy Metals in Surface Water and Sediment of a Typical River Network Zone in Taihu Lake Region

In the peri-urban river network area of Wuxi,which could be classified into 5 parts,i.e.watercourses in the residential area,main river course in the industry area,main river course in the farming area,ditches of the farming area and fishpond area.Sampling was carried out in both autumn(dry) and summer(rainy) seasons.Concentrations of nitrogen,phosphorus and Cu,Zn,Pb,Cr,Cd in samples of surface water and sediment were determined and their spatial variations were studied.Results show that 1) industrial wastewater and domestic sewage were the main contributors of nitrogen and phosphorus pollution in the surface water,rather than agriculture fields.And they were scattered in distribution and extensive in impact.2) Concentrations of heavy metals in the water and sediment were elevated to varying extents in the above-listed 5 types of water zones.Heavy metal pollution was induced mainly by industrial activities and urban surface runoff.However,heavy metals in the surface water were transported mainly along the main river courses.In both dry season and rainy season,heavy metal concentrations in the main river course were higher than that in ditches of the farming area and heavy metal concentrations in the sediments of the main river courses decreased sharply with increasing distance away from the town,which indicates that the range of river water affected by heavy metal pollution was small.3) The prominent problem of the water environment in the Taihu Lake region was still nitrogen and phosphorus pollution,rather than heavy metal pollution.However,the potential risk of heavy metal pollution in the water should not be overlooked considering the high concentrations of heavy metals in the river sediments in and around towns.