Study On Groudnwater Nitrogen Contamination And The Effect Factors During Maize Growth Stage In People's Victory Canal Irrigation District

Groundwater is an important water source for agricultural irrigation and drinking,it plays an important role in food production,life and ecology.The management practices of groundwater irrigation and fertilizers application lead to serious groundwater level declining and groundwater pollution problems in irrigation districts.In order to study the present situation and influencing factors of nitrogen pollution of groundwater in irrigation district,this paper was conducted in the People's Victory Canal Irrigation District(PVCID)of Henan province,which is a typical irrigated area in the main grain-producing areas in North China Plain..During the maize growth stage from May to September in 2017,14 observation points were selected in PVCID.The groundwater depth and groundwater quality parameters(temperature,pH,DO,ORP,TDS and)were measured every month.Meanwhile,groundwater samples were collected to determine the contents of nitrogen in different forms(ammonium nitrogen,nitrate nitrogen,nitrite nitrogen and dissolved organic nitrogen)in laboratory.The spatial and temporal distribution characteristics and influencing factors of groundwater nitrogen pollution were analyzed.Main research contents and results are as follows:(1)The groundwater depth,temperature,pH,ORP,DO,TDS,and other parameters of groundwater were measured on site,and the contents of ?three-nitrogen?,DON,iron ion and manganese ion of groundwater were measured indoors,according to <Groundwater Quality Standard> implemented in 2018,the the groundwater pollution in this irrigated areas were analyzed.Ammonium nitrogen is the main pollutant in groundwater ?three-nitrogen? pollutants,for the total 70 water samples collected in this study,54% of these samples exceed ? standard for ammonium nitrogen.The nitrate nitrogen and nitrite nitrogen showed slightly pollution.68% of the samples exceed iron ion ? standard,51% of the samples exceed the manganese ion ? standard,and 43% of the samples exceeded the TDS ? standard(2)The spatial and temporal distribution of groundwater nitrogen elements in irrigation areas from May to September 2017 were analyzed,ArcGIS was used for spatial interpolation to obtain the spatial distribution map of groundwater nitrogen element in PVCID,besides,the percentage of different forms of nitrogen were analyzed.Main form of the total nitrogen is DON,and main form the total inorganic nitrogen is nitrate nitrogen.The nitrate nitrogen content of groundwater increased in July and September in PVCID.The contents of nitrite and ammonium nitrogen in groundwater were lower than nitrate nitrogen at each observation point,and the content of ammonium nitrogen increased in July and August in PVCID.According to the spatial and temporal distribution map,the groundwater nitrogen pollution in Qianlicun,Lidazhao,Sunxincun,are more serious than other areas in PVCID.(3)Factors influencing nitrogen migration and transformation of groundwater in PVCID were analyzed using correlation analysis and linear regression analysis,including fertilizer application,groundwater depth,and pH,ORP,DO,temperature iron and manganese ion of groundwater.The application of fertilizer increased the nitrogen content of groundwater;the nitrogen content could be lower with the increase of groundwater depth.The increase of pH value may enhance the denitrification and mineralization reaction,and reduce the nitrification and nitrification reaction,thus,it could lead to the decrease of nitrogen content in groundwater.As the ORP increased,nitrification reaction dominated,and the content of nitrate nitrogen and nitrite nitrogen increased.The increase of temperature may enhance the mineralization and denitrification reactions,leading to the decrease of DON,nitrate nitrogen,nitrite content,and the increase of ammonium nitrogen.