title: Assessment of sources and fate of nitrate in shallow groundwater of an agricultural area by using a multi-tracer approach.
abstract: 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.
authors.affiliation: 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.
authors.forename: Ernesto
authors.initials: E
authors.lastname: Pastén-Zapata
authors.affiliation: 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.
authors.forename: Rogelio
authors.initials: R
authors.lastname: Ledesma-Ruiz
authors.affiliation: Department of Land, Air and Water Resources, University of California, C.P. 95616 Davis, CA, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Harter
authors.affiliation: 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.
authors.forename: Aldo I
authors.initials: AI
authors.lastname: Ramírez
authors.affiliation: 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. Electronic address: jurgen@itesm.mx.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Mahlknecht
mesh_terms: D000383:Agriculture; D004784:Environmental Monitoring / Q000379:methods*; D005308:Fertilizers; D060587:Groundwater / Q000737:chemistry*; D008800:Mexico; D009566:Nitrates / Q000032:analysis*; D009587:Nitrogen Isotopes / Q000032:analysis; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D005308:Fertilizers; D009566:Nitrates; D009587:Nitrogen Isotopes; D014874:Water Pollutants, Chemical
keywords: Denitrification; Groundwater; Halides; Isotopes; Mexico; Nitrate; Tracer