张掖市地下水硝酸盐污染源的氮同位素研究

Studies of Nitrogen Isotopes in Sources of Nitrate Pollution in Groundwater Beneath the City of Zhangye

张掖市浅层水NO-3 浓度 1 .69～ 1 49.6mg/L ,均值 5 4 .1 7± 41 .97mg/L(n =1 5 ) ,深层水NO-3 浓度 3.89～ 82 .85mg/L ,均值 35 .65± 2 8.0 8mg/L(n =1 2 )。西北部污灌区大部分浅层水样的NO-3 -δ1 5N值在 + 9‰～ + 1 4‰之间 ,不但NO-3 浓度高 ,而且NH+4含量大 (达 1 0 5mg/L) ,说明地下水NO-3 来自灌溉的污水 ;东部非污灌区浅层水NO-3 -δ1 5N值变化在 + 9‰～ +1 1‰ ,指示地下水NO-3 来自动物粪便和生活污水 ;城区、南部和西部深层水绝大部分样品的NO-3 -δ1 5N值在 + 4‰～ + 7‰之间 ,指示地下水NO-3 主要来自矿化的土壤有机氮 ,结合Na+与Cl- 以及δ1 5N与NO-3 的相关图进一步分析 ,揭示δ1 5N小的一端还有显著的化肥的贡献。

NO- 3 concentrations in shallow groundwater beneath Zhangye ranged from 1.69 to 149.6mg/L,averaging 54.17±41.97mg/L in 15 samples.High NO- 3 concentrations was mainly distrubited in the northwestern part in the sewage irrigation area and secondly in the eastern part in the non-sewate irrigation area; Deep groundwater had NO- 3 concentrations ranging from 3.89 to 82.85mg/L,averaging 35.65±28.08mg/L in 15 samples.The distribution of high NO- 3 concentrations was mainly in the urban area,the southern part and the western part.The shallow groundwater in the northwestern part in the sewage irrigation area had NO- 3-δ 15N values ranging from +9‰ to +14‰,and not only high NO- 3 concentrations,but also a high levels of NH+ 4(as much as 105mg/L),which indicated NO- 3 in the groundwater derived from irrigated effluents.Shallow groundwater in the eastern part in the non-sewage irrigation area had NO- 3-δ 15N values ranging from +9‰ to +11‰,indicative of localized pollution by animal or sewage waste.The deep groundwater in the urban area,the southern part and the western part had mostly NO- 3-δ 15N values ranging from +4‰ to +7‰,indicating that NO- 3 in the groundwater derived from the mineralization of soil organic nitrogen.Integration of correlation diagrams of Na against Cl- or δ 15N against NO- 3 further revealed an obvious fertilizer contributions for the light end of δ 15N of the soil organic range.