| Groundwater samples were collected from intensive agricultural regions of 13 districts in Beijing from 2005 to 2012 to determine the status of nitrate nitrogen（N） contamination in groundwater. The results indicated that the mean concentration of nitrate-N of all samples analysed in Beijing was 6.34 mg NO-3-N·L-1. There were 19.36% of the samples exceeding 10 mg·L-1, and 6.73% of the samples exceeding 20 mg·L-1. The annual average concentration of nitrate-N varied from 5.85 mg·L-1 to 6.93 mg·L-1, which met the category III national water quality standard. Nitrate leaching was enhanced by rainfall and higher concentrations of nitrate-N in groundwater were observed after rainy seasons. The nitrate-N concentration in groundwater was affected by the land use system in the following order：vegetable field>arable cropping>other land uses>orchards, with the mean nitrate-N concentration being 7.66 mg·L-1, 6.15 mg·L-1, 5.58 mg·L-1 and 4.97 mg·L-1, respectively. The nitrate-N concentration in groundwater decreased with increasing groundwater depth, and the average concentration within 30 m was 12.71 mg·L-1, exceeding the WHO drinking water guideline. |
