Study On Traceability Method Of Nitrogen Pollution In Groundwater Of Domestic Waste Landfill In Agricultural Area

At present,the groundwater quality in China is generally poor,especially in domestic waste landfills and agricultural areas,and nitrogen pollution has become one of the main pollutants in groundwater.However,at present,the traceability study of nitrogen pollution in groundwater of landfills and agricultural areas is independent,and there is no Traceability Method for nitrogen pollution in groundwater of domestic waste landfills in agricultural areas,which makes it possible to carry out traceability research in this area.The prevention and control of groundwater nitrogen pollution pollution lacks pertinence.In this paper,a set of traceability methods of nitrogen pollution in groundwater of domestic waste landfill in agricultural area is constructed by means of mathematical statistics,chemical analysis of water quality and stable isotope traceability,which provides technical guidance for the prevention and control of nitrogen pollution in groundwater of this kind of area.The main research contents are as follows:（1）Based on the pollution characteristics of domestic refuse landfills and agricultural areas,a traceability method of groundwater nitrogen pollution of domestic refuse landfills in agricultural areas is established,which is"field investigation-space-time analysis-chemical analysis-isotope analysis".The specific steps are as follows:（1）Firstly,field investigation and monitoring are carried out.That is to say,from seven aspects:topography,climate,hydrogeology,surface runoff,distribution and characteristics of pollution sources,land use status and agricultural production status,to carry out on-site investigation,monitoring and data collection of groundwater in domestic waste landfills in agricultural areas.（2）Secondly,the spatio-temporal analysis of water quality is used to trace the source.That is to say,through descriptive statistics of groundwater nitrogen pollution and water quality indexes closely related to pollution sources in the region,we can grasp the main pollution indexes and pollution degree of groundwater in the region;then we can analyze the significant differences and influencing factors of groundwater quality between the high-water period and the low-water period;finally,through the isoline distribution of groundwater quality index concentration and the variation law of each monitoring index,we can combine them.The types of land use and distribution of pollution sources in the region are traced to the source of nitrogen pollution in groundwater.（3）If the time-space analysis method can not achieve traceability,then the water quality chemical analysis method can be used to traceability.That is to say,on the basis of understanding the characteristic pollution indexes of typical pollution sources in the region,all water quality indexes related to pollution sources are taken as original variables for factor analysis,and after obtaining the main factors,the composition of the indexes and their scores at the monitoring wells are analyzed,and the pollution sources represented by the main factors are inferred;then,the scores of the main factors at the monitoring wells are taken as variables and monitored.The groundwater zoning under the influence of various pollution sources is obtained by cluster analysis of logging data.By analyzing the main factors including nitrogen pollution,the source of nitrogen pollution in regional groundwater can be traced.（4）If the chemical analysis method can not achieve traceability,the stable double isotope method of nitrate nitrogen and oxygen is used to traceability finally.That is to say,on the premise of judging whether there is general denitrification in regional groundwater,the groundwaterδ¹⁵N-NO₃^—、δ¹⁸O-NO₃^—are compared withδ¹⁵N-NO₃^—、δ¹⁸O-NO₃^—range of major pollution sources in the region to realize qualitative analysis of NO₃^—-N sources,and then the SIAR isotope mixing model is used to calculate the contribution rate of each pollution source to NO₃^—-N in groundwater combined with groundwater.The composition and correlation of nitrogen pollution can realize the qualitative and quantitative traceability of regional groundwater nitrogen pollution.（2）This method was applied to the traceability investigation of groundwater in a hydrological year of domestic refuse landfill in a county’s red beds agricultural area.The results show that:（1）The results show that NO₃^—-N in groundwater mainly comes from domestic sewage discharge and agricultural fertilizer application,and NH₄⁺-N mainly comes from livestock manure and landfill leachate.（2）By using the analytical Traceability Method of water quality chemistry,it is concluded that regional groundwater is mainly affected by four main environmental factors,namely,F1 landfill,whose indicators are TDS,EC and Cl^—;F2 fish pond,whose indicators are NH₄⁺-N,TP and COD_Mn;F3 agriculture and living source,whose indicators are TN and NO₃^—-N;F4 rainfall and other natural factors,whose indicators are total hardness and pH;Moreover,F1 and F2 are the main continuous input sources of groundwater pollution,contributing mainly to NH₄⁺-N pollution,while F3 and F4are greatly affected by seasonal and spatial changes,contributing mainly to NO₃^—-N pollution.（3）Using the stable double isotope Traceability Method of nitrate nitrogen and oxygen,it is concluded that NO₃^—-N in regional groundwater is mainly affected by atmospheric nitrogen deposition,soil organic nitrogen,manure,domestic sewage and agricultural chemical fertilizer.The SIAR model was used to calculate that the contribution rate of domestic sewage discharge to groundwater NO₃^—-N was the highest in dry season,reaching 53.68±19.23%,followed by livestock farming（23.82+16.24%）,soil organic nitrogen decomposition and leaching（15.76±13.23%）,fertilizer application（4.88±4.31%）and rainwater（1.85±1.15%）;and in wet season,the contribution of domestic sewage discharge to groundwater NO3-N was the highest.The highest rate was（33.73±13.62%）,followed by livestock and poultry farming（29.80±15.35%）,soil organic nitrogen decomposition and leaching（29.11±16.3%）,fertilizer application（5.93±5.07%）and rainwater（1.43±1.23%）.