Nitrate Legacy in a Tropical and Complex Fractured Volcanic Aquifer System
Nitrate legacy is affecting groundwater sources across the tropics. This study describes isotopic and ionic spatial trends across a tropical, fractured, volcanic multi-aquifer system in central Costa Rica in relation to land use change over four decades. Springs and wells (from 800 to 2,400 m asl)...
| Autores Principales: | Sánchez-Gutiérrez, Rolando, Sanchez-Murillo, Ricardo, Esquivel-Hernández, Germain, Birkel, Christian, Boll, J., Rojas-Jiménez, L. D., Castro-Chacón, L. |
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| Formato: | Artículo |
| Idioma: | Inglés |
| Publicado: |
John Wiley & Sons (Estados Unidos)
2024
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| Materias: | |
| Acceso en línea: |
http://hdl.handle.net/11056/27790 https://doi. org/10.1029/2023JG007554 |
| Sumario: |
Nitrate legacy is affecting groundwater sources across the tropics. This study describes isotopic
and ionic spatial trends across a tropical, fractured, volcanic multi-aquifer system in central Costa Rica in
relation to land use change over four decades. Springs and wells (from 800 to 2,400 m asl) were sampled for
NO3 − and Cl − concentrations, δ 18Owater, δ 15NNO3, and δ 18ONO3. A Bayesian isotope mixing model was used to
estimate potential source contributions to the nitrate legacy in groundwater. Land use change was evaluated
using satellite imagery from 1979 to 2019. The lower nitrate concentrations (<1 mg/L NO3 −N) were reported in
headwater springs near protected forested areas, while greater concentrations (up to ∼63 mg/L) were reported
in wells (mid- and low-elevation sites in the unconfined unit) and low-elevation springs. High-elevation springs
were characterized by low Cl − and moderate NO3 −/Cl − ratios, indicating the potential influence of soil nitrogen
(SN) inputs. Wells and low-elevation springs exhibited greater NO3 −/Cl − ratios and Cl − concentrations above
100 μmol/L. Bayesian calculations suggest a mixture of sewage (domestic septic tanks), SN (forested recharge
areas), and chemical fertilizers (coffee plantations), as a direct result of abrupt land use change in the last
40 years. Our results confirm the incipient trend in increasing groundwater nitrogen and highlight the urgent
need for a multi-municipal plan to transition from domestic septic tanks to regional sewage treatment and
sustainable agricultural practices to prevent future groundwater quality degradation effectively. |
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