Distribution Characteristics And Migration Of Inorganic Nitrogen In Shallow Groundwater Around Poyang Lake

In this paper,the area around Poyang Lake is taken as the study area,the shallow groundwater as the research object,on the basis of field investigation,using the hydrogeochemical method and environmental isotope techniques,analyzes the shallow groundwater hydrogeochemical characteristics,nitrogen distribution characteristics and the nitrate nitrogen source,using the single component analysis method,the comprehensive index evaluation method and the fuzzy comprehensive evaluation method to evaluate the shallow groundwater quality.Through the research,the following main understandings and conclusions are obtained:（1）The hydrochemical types of surface water are mainly HCO₃-Ca,and the hydrochemical types of shallow groundwater are quite diverse,with a total of 19 types.The hydrogen and oxygen isotope data indicate that the main source of shallow groundwater is local meteoric precipitation,and the surface water is mainly controlled by the dissolution of salt rocks,in which Na⁺and Cl^-are mainly derived from the dissolution of rock salt,while Ca²⁺,Mg²⁺and SO₄^2-may be derived from the dissolution of gypsum and magnesium salt minerals.（2）Spatial and temporal distribution characteristics of different forms of nitrogen:in the shallow groundwater in the wet and dry periods,the concentration of nitrate nitrogen is0.7～21.6 mg/L and 0.5～15.7 mg/L,respectively.There is an obvious spatial and temporal difference.The concentration of ammonia nitrogen is 0.00～4.70 mg/L and 0.00～11.00 mg/L,respectively.The high value point of ammonia nitrogen concentration was located in the west of typical agricultural irrigation area.The concentration of nitrite nitrogen was 0.000～0.520mg/L and 0.002～0.330 mg/L,respectively.Rainfall,irrigation,land use type,fertilizer application and so on can affect the content and distribution of nitrogen in groundwater.（3）The nitrogen and oxygen isotope range of nitrate nitrogen in shallow groundwater is-1.07‰～12.88‰and 0.47‰～20.43‰,respectively.Combined with the hydrochemical analysis,the main source of nitrate nitrogen in shallow groundwater were as fellow:The mixing of nitrogen in soil with manure and sewage;The mixing of nitrogen in soil with manure and sewage,fertilizers and NH₄⁺in rainfall;The mixing of manure and sewage with fertilizers and NH4+from rainfall;The NH₄⁺in fertilizers and rainfall;and NO₃^-fertilizer.（4）Single index evaluation method,comprehensive evaluation method and fuzzy comprehensive evaluation method are used to evaluate the water quality of shallow groundwater,results show that more than 80%of the shallow groundwater in the study area can meet the requirements of the water quality,but there is a potential risk of nitrogen pollution.