北京平原农区地下水硝态氮污染状况及其影响因素研究

研究了北京市平原农区4种埋深地下水的硝态氮污染状况及影响因素.结果表明,北京市平原农区深层地下水硝态氮污染已不容乐观,浅层地下水污染尤为严重.145眼深度在120～200 m的饮用井硝态氮含量最低,平均为5.16 mg L^-1,超标率（NO3-N≥10 mg L^-1）和严重超标率（NO3^--N≥20mg L^-1）分别为13.8%和6.9%;336眼深度在70～100 m的农灌井硝态氮平均含量为5.98 mg L^-1,超标率和严重超标率分别为24.1%和8.6%;而41眼深度在6～20 m的手压井硝态氮平均含量达14.01 mg L^-1,超标率和严重超标率分别高达46.3%和31.7%;77眼深度在3～6 m的浅层地下水质量最差,硝态氮含量平均为47.53 mg L^-1,超标率和严重超标率分别达80.5%和66.2%.远郊地下水质量明显优于近郊,其中饮用水超标率近郊为38.7%,远郊为3.0%;农灌水超标率近郊为52.6%,远郊为15.3%.地下水硝态氮污染在很大程度上受机井所处周边环境的影响,菜区特别是老菜区的地下水污染程度远远重于其他地区.140眼粮田农灌井硝态氮平均含量为2.45 mg L^-1,超标率仅为8.5%;而189眼菜田农灌井平均含量为8.66 mg L^-1,超标率高达36.0%;26个冬小麦夏玉米轮作粮田浅层地下水平均含量为18.02 mg L^-1,超标率为55.4%,43个保护地菜田浅层地下水样本平均含量为72.42 mg L^-1,超标率达100%.综合本研究结果,北京市平原农区地下水中的硝态氮主要来源于地表淋溶,过量施用氮肥是地下水硝态氮污染的主要原因.

NITRATE CONTAMINATION OF GROUNDWATER AND ITS AFFECTING FACTORS IN RURAL AREAS OF BEIJING PLAIN

Nitrate content of groundwater was surveyed in rural areas of the Beijing Plain from 1999 to 2000.The wells covered in the survey were grouped into four types according to depth and use,i.e.drinking wells(DW) about 120 to 200 m in depth,irrigation wells(IW) about 70 to 100 m in depth,hand-pumping wells(HW) about 6 to 20 m in depth and shallow groundwater(SG) about 3 to 6 m in depth.Findings of the survey show that nitrate content of groundwater is inversely related to depth of the wells.The deeper the well,the lower the nitrate content of the groundwater.NO~-_3-N contents of the groundwaters from 145 DWs,336 IWs,41 HWs and 77 SGs averaged out at 5.16 mg L~(-1),5.98 mg L~(-1),14.01 mg L~(-1)and 47.53 mg L~(-1),respectively,and 13.8%,24.1%,46.3% and 80.5% of the four types of waters exceeded 10 mg L~(-1) NO~-_(3)-N,the international maximum permissible limit for drinking water.Nitrate contamination of groundwater from deep wells was somewhat acceptable,while that of shallow groundwater was terrible.The situation in the suburbs of Beijing,such as Haidian,Fengtai and Chaoyang Districts,was much worse than in the exurbs of Beijing,such as Shunyi,Tongzhou,Changping,Daxing Districts.In the suburbs,38.7% of the DWs and 52.6% of the IWs had NO~-_(3)-N content above 10 mg L~(-1),but in the exburbs,only 3.0% of DWs and 15.3% of IWs did.Nitrate content of Groundwater from wells was remarkably affected by surrounding conditions of the wells.In wells located in vegetable fields,especially old vegetable fields it was more serious than in cereal fields or farmyard.The mean value of 140 IWs located in cereal fields was 2.45 mg L~(-1),and only 8.5% of the wells exceeded the limit in NO~-_(3)-N content,while that of 189 IWs in vegetable fields was as high as 8.66 mg L~(-1),and 36.0% of the wells did,And also the mean value of 26 SGs located in fields of winter wheat in rotation with summer maize was 18.02 mg L~(-1),and 55.4% of the SGs went above the limit,while that of 43 SGs under greenhouses reached as high as 72.42 mg L~(-1),and 100% did.Nitrate leaching as a result of overfertilization in vegetable production is the major cause of nitrate contamination of groundwater in rural areas of the Beijing Plain.