Trends in Nitrate Concentrations and Determination of its Origin Using Stable Isotopes (¹⁸O and¹⁵N) 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 ( 15 N NO3 À and 18 O NO3 À ) 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.

Occurrence of nitrate in Tanzanian groundwater aquifers: A review

“…Discharge of nitrate contaminated groundwater to water bodies with low nitrate concentrations may result in eutrophication (Spalding and Exner 1993). The presence of nitrate at elevated concentration in the groundwater may be an indirect indicator of the presence of other contaminants derived from human activities (Reynolds-Vargas et al 2006). A full understanding of the natural concentration, possible sources and biogeochemical transformation of nitrate is required for a successful groundwater management strategy.…”

“…Agriculture is the main source of nitrate in groundwater from rural areas due to application of organic and inorganic fertilisers (Jalali 2005;Ju et al 2006;Reynolds-Vargas et al 2006;Srinivasamoorthy et al 2009;Divya and Belagali 2012;Dragon 2012). Expansion of agricultural activities will be associated with increased use of fertilisers and pesticides.…”

“…The usefulness of groundwater resources, however, is being compromised by contamination due to natural and human activities (Nkotagu 1996a, b;Tredoux et al 2000;Reynolds-Vargas et al 2006). Groundwater quality degradation has been widely reported from both urban and rural areas in developed and developing countries.…”

“…Potential anthropogenic source of groundwater contamination is domestic sewage especially onsite sanitation systems like pit latrines, cesspits and soak away pits (Nkotagu 1996a;Tredoux et al 2000;Reynolds-Vargas et al 2006;Kiptum and Ndambuki 2012). Other sources include industrial effluents, leachate from solid waste dumpsites, leakage from fuel filling stations, automobile and repair garages, industrial workshops and agriculture (Eckhardt and Stackelberg 1995;Goulding 2000;Jalali 2005;Srinivasamoorthy et al 2009).…”

Nitrato nas águas subterrâneas do Sistema Aquífero Bauru, área urbana do Município de Marília (SP)

“…O nitrato é o contaminante com maior frequência em aquíferos no mundo (REYNOLDS--VARGAS et al 2006). Esse parâmetro é utilizado, mundialmente, como indicador da contaminação das águas subterrâneas devido à sua alta mobilidade, podendo atingir extensas áreas.…”