title: Trends in nitrate concentrations and determination of its origin using stable isotopes (18O and 15N) in groundwater of the Western Central Valley, Costa Rica.
abstract: A study was conducted to evaluate long-term trends in nitrate concentrations and to try to identify the origin of nitrate using stable isotopes (15N(NO3-) and 18O(NO3-)) in the aquifers of the western Central Valley, Costa Rica, where more than 1 million people depend on groundwater to satisfy their daily needs. Data from 20 sites periodically sampled for 4 to 17 years indicate an increasing trend in nitrate concentrations at five sites, which in a period ranging from 10 to 40 years, will exceed recommended maximum concentrations. Results of isotopic analysis indicate a correspondence between land use patterns and the isotopic signature of nitrate in groundwater and suggest that urbanization processes without adequate waste disposal systems, followed by coffee fertilization practices, are threatening water quality in the region. We conclude that groundwater management in this area is not sustainable, and that land use substitution processes from agricultural activity to residential occupation that do not have proper sewage disposal systems may cause a significant increment in the nitrate contaminant load.
authors.affiliation: Environmental Hydrology Laboratory, Universidad Nacional, Heredia, Costa Rica. jreynold@una.ac.cr
authors.forename: Jenny
authors.initials: J
authors.lastname: Reynolds-Vargas
authors.forename: Julio
authors.initials: J
authors.lastname: Fraile-Merino
authors.forename: Ricardo
authors.initials: R
authors.lastname: Hirata
mesh_terms: D000383:Agriculture; D003364:Costa Rica; D005308:Fertilizers / Q000009:adverse effects; D009566:Nitrates / Q000032:analysis*; D009587:Nitrogen Isotopes; D010103:Oxygen Isotopes; D014505:Urban Population; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000032:analysis*; D014881:Water Supply / Q000592:standards
chemical_list: D005308:Fertilizers; D009566:Nitrates; D009587:Nitrogen Isotopes; D010103:Oxygen Isotopes; D014874:Water Pollutants, Chemical