L. D. Rojas‐Jiménez

Universidad Hispanoamerica

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Ricardo Sánchez‐Murillo

The University of Texas at Arlington

Germain Esquivel‐Hernández

Universidad Nacional

Christian Birkel

Universidad de Costa Rica

Laura Castro‐Chacón

Universidad Hispanoamerica

José Vargas‐Víquez

Universidad Hispanoamerica

Jan Boll

Washington State University

Lucía Ortega

International Atomic Energy Agency

Michael Sánchez-Guerrero

Sylvia Dee

Rice University

N. Gutiérrez‐Sibaja

Universidad Nacional

Cooperative Institutions

Universidad Nacional

Universidad de Costa Rica

North Carolina State University

The University of Texas at Arlington

Universidad Hispanoamerica

North Central State College

University of Idaho

Waters (United States)

Florida International University

University of Washington

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DOC Transport and Export in a Dynamic Tropical Catchment

Journal of Geophysical Research Biogeosciences (2019)

Ricardo Sánchez‐Murillo Luis Romero Joaquín Jiménez-Antillón Jéssica Salas-Navarro Leonardo Corrales-Salazar

Abstract Dissolved organic carbon (DOC) transport and export from headwater forests into freshwaters in highly dynamic tropical catchments are still understudied. Here we present a DOC analysis (2017) in a pristine and small (~2.6 km 2 ) tropical catchment of Costa Rica. Storm flows governed a rapid surface and lateral allochthonous DOC transport (62.2% of the annual DOC export). Cross‐correlation analysis of rainfall and stream discharge indicated that DOC transport occurred on average ~1.25 hr after the rainfall maxima, with large contributions of event water, ranging from 42.4±0.3% up to 98.2±0.3% of the total discharge. Carbon export flux (annual mean=6.7±0.1 g C · m ‐2 · year ‐1 ) was greater than values reported in subtropical and temperate catchments. Specific ultraviolet absorbance indicated a mixture of hydrophobic humic and hydrophilic nonhumic matter during both baseflow and storm events. Our results highlight the rapid storm‐driven DOC transport and export as well as low biogeochemical attenuation during baseflow episodes in a climate sensitive hot spot. By understanding the key factors controlling the amount of organic carbon transported to streams in dynamic tropical landscapes, better global‐ and catchment‐scale model assessments, conservation practices, and water treatment innovations can be identified.

Base flow

Biogeochemical Cycle

Discharge

10.1029/2018jg004897

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Citations (21)

From mountains to cities: a novel isotope hydrological assessment of a tropical water distribution system

Figshare (2020)

Ricardo Sánchez‐Murillo Germain Esquivel‐Hernández Christian Birkel Lucía Ortega Michael Sánchez-Guerrero

Water use by anthropogenic activities in the face of climate change invokes a better understanding of headwater sources and lowland urban water allocations. Here, we constrained a Bayesian mixing model with stable isotope data (2018–2019) in rainfall (N = 704), spring water (N = 96), and surface water (N = 94) with seasonal isotope sampling (wet and dry seasons) of an urban aqueduct (N = 215) in the Central Valley of Costa Rica. Low δ¹⁸O rainfall compositions corresponded to the western boundary of the study area, whereas high values were reported to the northeastern limit, reflecting the influence of moisture transport from the Caribbean domain coupled with strong orographic effects over the Pacific slope. The latter is well-depicted in the relative rainfall contributions (west versus east) in two headwater systems: (a) spring (68.7 ± 3.4 %, west domain) and (b) stream (55.8 ± 3.9 %, east domain). The aqueduct exhibited a spatial predominance of spring water and surface water during a normal wet season (78.7 %), whereas deep groundwater and spring water were fundamental sources for the aqueduct in the dry season (69.4 %). Our tracer-based methodology can help improve aqueduct management practices in changing climate, including optimal water allocation and reduced evaporative losses in the dry season.

10.6084/m9.figshare.13293055

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Deciphering complex groundwater age distributions and recharge processes in a tropical and fractured volcanic multi‐aquifer system

Hydrological Processes (2022)

Ricardo Sánchez‐Murillo Irene Montero‐Rodríguez José Leonardo Corrales-Salazar Germain Esquivel‐Hernández Laura Castro‐Chacón

Abstract Groundwater recharge in highly fractured volcanic aquifers in the humid tropics remains poorly understood. In this region, rapid demographic growth and unregulated land use change are resulting in extensive surface water pollution and a large dependency on groundwater extraction. Here we present a multi‐tracer approach including δ 18 Oδ 2 H, 3 H/ 3 He dating, and noble gases (NG) within the most prominent multi‐aquifer system of central Costa Rica, with the objective to assess dominant groundwater recharge mechanisms and age distributions. We sampled wells and large springs across an elevation gradient from 868 to 2421 m asl. Our results indicate relatively young apparent ages ranging from 0.0 ± 3.2 up to 43.5 ± 7.6 years within the unconfined aquifer system. Helium isotopes (R/R a up to 5.4) indicate a dominant signal from the upper mantle and preclude 3 H/ 3 He dating in 50% of the samples. Potential recharge elevations (based on NG and δ 18 O) ranged from ~1350 to 2670 m asl. NG‐derived recharge temperatures ranged from 11.0°C to 19.4°C. Recharge estimates varied from 129 ± 78 to 1605 ± 196 mm/yr with a mean value of 642 ± 117 mm/yr, representing 20.1 ± 4.0% of the total mean annual rainfall as effective recharge. The shallow unconfined aquifer is characterized by young and rapidly infiltrating water, whereas the deeper aquifer units have relatively older water (>60 years). These results are intended to guide the delineation and mapping of critical recharge areas in mountain headwaters to enhance water security and sustainability in the most important headwater dependent systems of Costa Rica.

Depression-focused recharge

10.1002/hyp.14521

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From mountains to cities: a novel isotope hydrological assessment of a tropical water distribution system

Isotopes in Environmental and Health Studies (2020)

Ricardo Sánchez‐Murillo Germain Esquivel‐Hernández Christian Birkel Lucía Ortega Michael Sánchez-Guerrero

(2020). From mountains to cities: a novel isotope hydrological assessment of a tropical water distribution system. Isotopes in Environmental and Health Studies: Vol. 56, Environmental isotope applications in Latin America and the Carribean region, pp. 606-623.

Dry season

Aqueduct

Wet season

10.1080/10256016.2020.1809390

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Citations (13)

ENSO sentinels in the Americas' humid tropics: We need combined hydrometric and isotopic monitoring for improved El Niño and La Niña impact prediction

Hydrological Processes (2023)

Ricardo Sánchez‐Murillo Christian Birkel Jan Boll Germain Esquivel‐Hernández L. D. Rojas‐Jiménez

Abstract This Scientific Briefing presents results from a nearly 10‐year hydrometric and isotope monitoring network across north‐central Costa Rica, a region known as a headwater‐dependent system. This monitoring system has recorded different El Niño and La Niña events and the direct/indirect effects of several hurricane and tropical storm passages. Our results show that El Niño‐Southern Oscillation (ENSO) exerts a significant but predictable impact on rainfall amount anomalies, groundwater level and spring discharge, as evidenced by second‐order water isotope parameters (e.g., line conditioned‐excess or line‐conditioned (LC)‐excess). Sea surface temperature anomaly (El Niño Region 3) is correlated with a reduction in mean annual and cold front rainfall across the headwaters of north‐central Costa Rica. During El Niño conditions, rainfall is substantially reduced (up to 69.2%) during the critical cold fronts period, limiting groundwater recharge and promoting an early onset of minimum baseflow conditions (up to 5 months). In contrast, La Niña is associated with increased rainfall and groundwater recharge (up to 94.7% during active cold front periods). During La Niña, the long‐term mean spring discharge (39 Ls −1 ) is exceeded 63–80% of the time, whereas, during El Niño, the exceedance time ranges between 26% and 44%. The regional hydroclimatic variability is also imprinted on the hydrogen and oxygen isotopic compositions of meteoric waters. Drier conditions favoured lower LC‐excess in rainfall (−17.3‰) and spring water (−6.5‰), whereas wetter conditions resulted in greater values (rainfall = +17.5‰; spring water = +10.7‰). The lower and higher LC‐excess values in rainfall corresponded to the very strong 2014–2016 El Niño and 2018 La Niña, respectively. During the recent triple‐dip 2021–23 La Niña, LC‐excess exhibited a significant and consistently increasing trend. These findings highlight the importance of combining hydrometric, synoptic and isotopic monitoring as ENSO sentinels to advance our current understanding of ENSO impacts on hydrological systems across the humid Tropics. Such information is critical to constraining the 21st century projections of future water stress across this fragile region.

Base flow

Anomaly (physics)

Limiting

10.1002/hyp.15027

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Isotopic composition in precipitation and groundwater in the northern mountainous region of the Central Valley of Costa Rica

Isotopes in Environmental and Health Studies (2016)

Ricardo Sánchez‐Murillo Germain Esquivel‐Hernández Oscar Sáenz-Rosales Gilberto Piedra-Marín Alicia Fonseca-Sánchez

The linkage between precipitation and recharge is still poorly understood in the Central America region. This study focuses on stable isotopic composition in precipitation and groundwater in the northern mountainous region of the Central Valley of Costa Rica. During the dry season, rainfall samples corresponded to enriched events with high deuterium excess. By mid-May, the Intertropical Convergence Zone poses over Costa Rica resulting in a depletion of 18O/16O and 2H/H ratios. A parsimonious four-variable regression model (r2 = 0.52) was able to predict daily δ18O in precipitation. Air mass back trajectories indicated a combination of Caribbean Sea and Pacific Ocean sources, which is clearly depicted in groundwater isoscape. Aquifers relying on Pacific-originated recharge exhibited a more depleted pattern, whereas recharge areas relying on Caribbean parental moisture showed an enrichment trend. These results can be used to enhance modelling efforts in Central America where scarcity of long-term data limits water resources management plans.

δ18O

Intertropical Convergence Zone

Dry season

10.1080/10256016.2016.1193503

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Citations (31)

Connection to deep groundwater alters ecosystem carbon fluxes and budgets: an example from a Costa Rican rainforest (Invited)

AGU Fall Meeting Abstracts (2011)

David P. Genereux Christopher L. Osburn Laura A. Nagy S. F. Oberbauer L. D. Rojas‐Jiménez

Puerto rican

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Nitrate Legacy in a Tropical and Complex Fractured Volcanic Aquifer System

Journal of Geophysical Research Biogeosciences (2023)

Rolando Sánchez‐Gutiérrez Ricardo Sánchez‐Murillo Germain Esquivel‐Hernández Christian Birkel Jan Boll

Abstract 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 NO 3 − and Cl − concentrations, δ 18 O water , δ 15 N NO3 , and δ 18 O NO3 . 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 NO 3 − 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 NO 3 − /Cl − ratios, indicating the potential influence of soil nitrogen (SN) inputs. Wells and low‐elevation springs exhibited greater NO 3 − /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.

10.1029/2023jg007554

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Citations (4)