The effects of land use change and irrigation water resource on nitrate contamination in shallow groundwater at county scale

The objective of this study was to assess the impacts of land use changes and irrigation water resource on the nitrate contamination in shallow groundwater. 394 water samples were sampled from the same irrigation wells during a period of five years (from 2002 to 2007) in Huantai County in the North China Plain. NO3-N concentration in irrigation wells was measured. Geostatistical method combined with GIS technique was used to analyze the spatio-temporal distribution of groundwater NO3-N concentrations in Huantai County. Land use type and irrigation water resource were combined with the variation of NO3-N concentrations by statistical approach to investigate the relationship between them. The distribution map showed that the percentages of area increased by 13.06%, 14.37%, 12.23% and 3.85% for that had nitrate concentrations of 10-15, 15-20, 20-30 mg L−1 and greater than 30 mg L−1 for shallow groundwater, respectively, while decreased by 28.87% and 14.63% for 0-5 and 5-10 mg L−1. In the well-irrigated field, the NO3-N concentrations in shallow groundwater had increased for vegetables, wheat-vegetables and wheat-maize rotations. In contrast, fast-growing tree system could act as a buffer to retain shallow groundwater nitrate content which resulted in reduced NO3-N concentrations. Under the same land use condition, irrigation with sewage, or well and sewage by turns would both enormously add nitrate to groundwater.