Nitrate isotopic values are often used as a tool to identify sources of nitrate in order to effectively manage ground water quality. In this study, the concentrations of NO₃⁻, NO₂⁻, and NH₄⁺ from 50 boreholes and shallow wells in the Singida and Manyoni Districts were analyzed during the dry and wet seasons, followed by identification of nitrate sources using the hydrochemical method (NO₃⁻/Cl⁻) and stable isotope (δ¹⁵N and δ¹⁸O) techniques. Results showed that NO₂⁻ and NH₄⁺ concentrations were very low in both seasons due to the nitrification process. The concentrations of NO₃⁻ ranged from 2.4 ppm to 929.6 ppm with mean values of , during the dry season and from 2.4 ppm to 1620.0 ppm with mean values of , during the wet season. The higher NO₃⁻ contamination observed in the wet season could be due to rainfall which accelerated the surface runoff that collects different materials from various settings into the ground water sources. Nitrate source identification through hydrochemical technique revealed that most nitrates originated from sewage effluents and/or organic wastes such as manure. Likewise, the mean values of δ¹⁵N-NO₃⁻ ( and ) and the mean values of δ¹⁸O-NO₃⁻( and ) suggest that 80% of boreholes and 52% of shallow wells were dominated with nitrate from sewage effluents and/or manure as most ground water sources were situated in densely populated areas with congested and poorly constructed onsite sanitation facilities such as pit latrines and manure. Therefore, to reduce nitrate pollution in the study area, a central sewer must be constructed to treat the discharged wastes. Also, groundwater harvesting should consider the proper principles for groundwater harvesting recommended by the respective authority to minimize chances of contamination and hence prevention of health risk.

中文翻译：

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坦桑尼亚半干旱地区地下水含水层中硝酸盐的来源

硝酸盐同位素值通常用作识别硝酸盐来源的工具，以有效管理地下水质量。本研究在干湿季节对Singida 和Manyoni 区50 个钻孔和浅井的NO ₃ ^-、NO ₂ ^-和NH ₄ ⁺浓度进行了分析，然后利用水化学方法识别了硝酸盐的来源(NO ₃ ^- /Cl ^- ) 和稳定同位素（δ ¹⁵ N 和δ ¹⁸ O）技术。结果表明，NO ₂ ^-和NH ₄ ⁺由于硝化过程，两个季节的浓度都非常低。NO ₃ ^-的浓度范围为 2.4 ppm 至 929.6 ppm，平均值为,在旱季从 2.4 ppm 到 1620.0 ppm，平均值为，在雨季。在雨季观察到的较高的 NO ₃ ^-污染可能是由于降雨加速了地表径流，这些径流将来自不同环境的不同材料收集到地下水源中。通过水化学技术识别硝酸盐来源表明，大多数硝酸盐来源于污水和/或有机废物，如粪便。同样， δ ¹⁵ N-NO ₃ ⁻ ( 和 )和δ ¹⁸ O-NO ₃ ⁻ ( 和 )表明 80% 的钻孔和 52% 的浅井主要来自污水和/或粪便中的硝酸盐，因为大多数地下水源位于人口稠密的地区，现场卫生设施拥挤且施工不良，例如坑式厕所和粪便。因此，为减少研究区的硝酸盐污染，必须建设中央下水道对排放的废物进行处理。此外，地下水收集应考虑相关当局推荐的适当的地下水收集原则，以尽量减少污染的机会，从而预防健康风险。