Effects Of Sewage Sludge Application On Leaching Processof Soil Dissolved Organic Carbon In Sandy Grassland

As social modernization and industry in China grow faster and faster,sludge production also increases rapidly.According to national statistics,municipal and rural sewage plants yearly release up to 300 million tons of wet sludge with moisture content of 80%.However,sludge is rich in organic matter,nitrogen phosphorus and other nutrition that is necessary to soil quality,in spite of large amount of heavy metal and organic pollutant threatening soil quality and people's health.Therefore,to some degree sludge is of economic value.For example,nutrition recycled from sludge could be applied to improve the quality of sandy soil and the degraded sandy land ecosystem,and also could help to prevent toxic and harmful substance from food chain and finally protect people's health.Dissolved organic carbon(DOC)is one of an important part of organic carbon in soil,which is water-soluble,cyclic in soil,of high biological activity,and degraded by microorganism.The dynamic equilibrium of DOC level in soil is correlated with the circulation of organic carbon.Leaching is important in material migration.Because of absorption,the quantity and quality of DOC in soil keeps changing,and the performance of absorption varies in different layers of soil on account of various solution chemical properties and soil mineral constituent.Hence,it is of practical significance to investigate the effect of sludge on leaching of DOC in sandy grassland soil when we predict the changes of organic carbon in soil improvement.The sampling site was located in Daqinggou ecological testing station of Shenyang Institute of Applied Ecology,Chinese Academy of Sciences.Undisturbed soil was collected in the wild.Sludge was sampled from a municipal sewage plant.With the materials above,experiments stimulated the effect of sludge of on leaching of DOC in soil,according to different rainfall conditions designed with reference to the precipitation characteristics at the sampling site.Soil columns with sludge and the control group were tested in leaching experiments,measured and analyzed to decide the level of DOC in samples of different soil layers.The results were as followed: in soil columns with sludge,DOC level was significantly higher than before(p<0.01);with 150 ml,300ml and 450 ml of rainfall,DOC levels were respectively increased by 35%,72% and 90% compared with the control group;with 1.75 mm·h-1,3 mm·h-1 and 4.75 mm·h-1 of rainfall intensity,DOC levels were respectively increased by 79%,80% and 90% compared with the control group;DOC levels of soil columns were significantly correlated with soil layers(p<0.05);DOC levels in soil were significantly increased with the amount and intensity of rainfall.In conclusion,DOC level in leaching solution was significantly correlated with the amount of rainfall,the intensity of rainfall and sludge(p<0.01).Undisturbed soil columns were under stimulation of all-year precipitation and analysis of DOC constituents and levels of different soil layers and leaching solution.The results were as followed: the levels of DOC and leaching solution of different soil layers with sludge were all significantly higher than the control group(p<0.01);with the development of leaching stimulation experiments,DOC levels of leaching solution tended to decrease gradually.