Centro del Agua para América Latina y el Caribe, Tecnológico de Monterrey, Av. Eugenio Garza Sada Sur No. 2501, C.P. 64849 Monterrey, Nuevo León, Mexico.
Department of Land, Air and Water Resources, University of California, C.P. 95616 Davis, CA, USA.
Sci Total Environ. 2014 Feb 1;470-471:855-64. doi: 10.1016/j.scitotenv.2013.10.043. Epub 2013 Nov 5.
Nitrate isotopic values are often used as a tool to understand sources of contamination in order to effectively manage groundwater quality. However, recent literature describes that biogeochemical reactions may modify these values. Therefore, data interpretation is difficult and often vague. We provide a discussion on this topic and complement the study using halides as comparative tracers assessing an aquifer underneath a sub-humid to humid region in NE Mexico. Hydrogeological information and stable water isotopes indicate that active groundwater recharge occurs in the 8000km(2) study area under present-day climatic and hydrologic conditions. Nitrate isotopes and halide ratios indicate a diverse mix of nitrate sources and transformations. Nitrate sources include organic waste and wastewater, synthetic fertilizers and soil processes. Animal manure and sewage from septic tanks were the causes of groundwater nitrate pollution within orchards and vegetable agriculture. Dairy activities within a radius of 1,000 m from a sampling point significantly contributed to nitrate pollution. Leachates from septic tanks caused nitrate pollution in residential areas. Soil nitrogen and animal waste were the sources of nitrate in groundwater under shrubland and grassland. Partial denitrification processes helped to attenuate nitrate concentration underneath agricultural lands and grassland, especially during summer months.
硝酸盐同位素值通常被用作了解污染来源的工具，以有效管理地下水质量。然而，最近的文献表明，生物地球化学反应可能会改变这些值。因此，数据解释变得困难且往往不明确。我们就这一主题进行了讨论，并使用卤化物作为比较示踪剂来补充研究，评估了墨西哥东北部一个亚湿润到湿润地区的含水层。水文地质信息和稳定的水同位素表明，在当前气候和水文条件下，8000 平方公里的研究区域内有活跃的地下水补给。硝酸盐同位素和卤化物比值表明硝酸盐的来源和转化具有多样性。硝酸盐的来源包括有机废物和废水、合成肥料和土壤过程。果园和蔬菜农业中地下水硝酸盐污染的原因是动物粪便和化粪池污水。在采样点半径 1000 米范围内的奶牛活动对硝酸盐污染有显著贡献。化粪池的渗滤液导致居民区的硝酸盐污染。在灌木林和草原下的地下水中，土壤氮和动物粪便是硝酸盐的来源。部分反硝化过程有助于在农业用地和草原下衰减硝酸盐浓度，尤其是在夏季。
