Nitrogen Load Of Agricultural Sources And Spatial Variations In The Taihu Lake Basin

The Taihu Lake basin with densely populated,developed industry and intensive agri-culture.However,pollution of the surface water,especially eutrophication,has influenced both the water supply and economic development of this region in recent years,with nitro-gen(N)is a major pollutant in the surface water.Agricultural source is one of the main sources of water pollution.Previous studies have showed that the contribution of total ni-trogen(TN)load from agricultural source was larger than point source pollution from in-dustrial and urban life,which result in the eutrophication of the Taihu Lake more seriousand becoming more and more significantly.In this study,to evaluate the agricultural N pol-lution load and to provide pollution control measures,three main sources of agricultural source pollution including cropland,livestock and poultry husbandry and aquaculture were analyzed through survey,monitoring,remote sensing,statistical data and GIS technologies.The results of this study are as follows:Total N load in the Taihu Lake basin was 101.9×106kg in 2013,with an average of 27.6 kg hm"2.The TN load from cropland was 50.4×106kg,accounting for 49.4%of the total agricultural N load,with an average of 13.6 kg·hm-2.Vegetable field was one of the major N pollution source from cropland,accounting for 31.9%of the total agricultural N.Large amount of fertilizer application with low utilization rate lead to high TN load from cropland.Therefore a large number of N enter into the water through runoff and leaching,and seriously impact on water environment.TN load of livestock and poultry husbandry was 44.4×106kg,accounting for 43.5%of the total agricultural N load,with an average of 12.0 kg·hm-2.The highest TN load of livestock and poultry husbandry was pig,followed by poultry.High discharge relate to its large number of livestock and low treatment rate of domestic sewage.TV load of aquaculture source was relatively low,for 7.3×106kg,ac-counting for 7.1%of the total agricultural N load,with an average of 2.0 kg·hm-2.The main TN load source of aquaculture was pond breed,accounting for 90.7%of aquaculture TN load.The high TN load of aquaculture associated with high input feed and unreasonabal aquaculture.Affected by terrain,climate,soil,hydrology,land use and management and other complex factors,the spatial variation of N pollution in the Taihu Lake basin was signifi-cantly different.Result showed that the main areas of high TN load were south areas of Taihu Lake basin include Jiaxing,Jiashan,Haiyan,while main areas of low TN load were Wuxi,Suzhou,Linan,Anji.Spatial variation of cropland source TN load presented higher in northwest and southeast while lower in the middle areas.The high TN load areas were Jurong,Jiashan,while the low TN load areas were Suzhou,Kunshan,Changzhou and Shanghai.Spatial variation of TN load from livestock and poultry husbandry TN load was higher in southeast than in northwest.The high TN load areas were Jiaxing,Haiyan,Jiashan and Fengxian in the southeast of Taihu Lake basin,while the low TN load areas were Anji,Linan in the southwest of Taihu Lake basin and other regions.Spatial variations of aquacul-ture TN load gradually reduce form west area to east.The areas with highest TN load of aquaculture were Kunshan,Huzhou Deqing and Jintai.The reason of High TN load of aq-uaculture related to developed pond breed and aquatic breed in those areas.According to the estimation of agricultural sources TN load and the analysis of its spatial variation of Taihu Lake basin,we identified the priority pollution control areas and the key agricultural pollution sources in this region.The priority pollution control areas of Taihu Lake basin were Jiaxing,Jiashan,Haiyan and so on.Cropland and livestock and poultry husbandry were the key pollution sources of those as the priority pollution control areas.The priority pollution control areas of cropland were Jurong and Jiashan.And the key pollution sources of Jurong were paddy field and dry land,while the key pollution source of Jiashan is vegetable field.The priority pollution control areas of livestock and poultry hus-bandry were Jiaxing,Haiyan,Jishan and Fengxian.And the priority pollution control areas of aquaculture were Kunshan,Huzhou,Deqing and Jintai.The measurements of cropland source controls include control the N fertilizer rate and the decrease of N loss pathway through,set isolation belt,intercepting ditch,construct wetland and so on.The managemen-ts of aquaculture including control the breeding area,reasonable planting aquatic plants,ecological farming and so on.While the controls of livestock and poultry husbandry should be included the improving the legal effect of the regulations,building relevant sewage treatment facilities and organic fertilizer production plants,and enhancing the treatment rate of domestic animal sewage and so on.