Spatial variability of groundwater nitrate-nitrogen and cause analysis of its pollution for irrigation area with reclaimed water

To analysis the spatial distribution of groundwater nitrate-nitrogen and its pollution causes of reclaimed water irrigation region in Beijing, based on geostatistics model and geostatistical analyst module of ArcGIS. The spatial distribution maps of groundwater nitrate-nitrogen and semi-variogram function was proposed, which represented the probability and structural characteristics. The results showed that the groundwater nitrate-nitrogen satisfied log normal distribution and one-order Gaussian model can capture the characteristics well in the reclaimed water irrigation region. The prediction of distance statistical correlation of groundwater nitrate-nitrogen was 9639.36 m, and the distance between two sampling sits should be smaller than this value. The nugget effect value was 0.43, which implied that nitrate-nitrogen concentration distribution was controlled by structural factors and human activity. Land use style and groundwater withdrawal intensity directly influenced the probability of groundwater nitrate-nitrogen pollution. The depth of monitoring wells was smaller, the decline of groundwater level was greater, the increase in groundwater nitrate-nitrogen was greater. The risk of nitrate-nitrogen pollution of groundwater caused by accumulated areas of reclaimed water maintained low. The study provides a reference for quantifying the groundwater pollution risk and security of wastewater utilization in agriculture.