兰州市地下水中“三氮”污染特征及成因

Distribution and source of nitrogen pollution in groundwater of Lanzhou city

以兰州市41组浅层地下水样品水化学组分测试结果为依据,研究兰州市地下水中"三氮"污染特征。结果表明:兰州浅层地下水中"三氮"污染较严重,NO_3-N超标率最高,超标率为51. 2%; NO_2-N和NH_4-N次之,超标率分别为26. 8%和12. 2%。"三氮"污染分布不均,局部区域呈面状污染。NO_3-N重污染区主要分布于兰州市城关区的掩埋垃圾填埋场和受地表排污沟渠污染区域,西固区的石油化工区,以及七里河区西南部的污灌区。兰州断陷盆地"三氮"超标点相对较少。含氮化肥使用、污水灌溉及生活污水入渗是地下水中NO_3-N的主要来源;工业废水入渗是地下水中NH_4-N的重要来源。污染源类型不同,地下水"三氮"污染程度和空间分布特征亦不同;氧化还原条件、包气带岩性结构特征、补径排条件是"三氮"迁移转化及其空间分布的主要影响因素。

41 shallow groundwater samples were collected from Lanzhou city and analyzed for their chemical composition,and the nitrogen pollution in groundwater in Lanzhou was studied.Generally,the shallow groundwater in Lanzhou city is significantly polluted by nitrate.51.2% of the groundwater samples have NO3-N concentration exceeded the drinking water standard,and the rates are 26.8% and 12.2% for NO2-N and NH4-N,respectively.Groundwater samples are polluted the most in the following areas: berried landfill and sewage irrigation area in Chengguan district,the petrochemical industry in Xigu district,and the wastewater irrigation district in the southwest of Qilihe district.The nitrogen pollution in the rural area of the Lanzhou plain is slight.While the irrigation of domestic wastewater and the use of nitrogenous fertilizer are the main source of nitrate in groundwater;the infiltration of industrial wastewater is the main source of ammonium.The redox condition,lithology of vadose zone,and the recharge and flow condition are the main factors affecting the transport and transformation of nitrogen pollution in the groundwater.