Ricardo Sánchez-Murillo

Tropical precipitation anomalies and d-excess evolution during El Niño 2014-16†

The last 2014-16 El Nino event was among the three strongest episodes on record. El Nino considerably changes annual and seasonal precipitation across the tropics. Here, we present a unique stable isotope data set of daily precipitation collected in Costa Rica prior to, during, and after El Nino 2014-16, in combination with Lagrangian moisture source and precipitation anomaly diagnostics. δ2H composition ranged from -129.4 to +18.1 (‰) while δ18O ranged from -17.3 to +1.0 (‰). No significant difference was observed among δ18O (P = 0.0186) and δ2H (P = 0.664) mean annual compositions. However, mean annual d-excess showed a significant decreasing trend (from +13.3 to +8.7 ‰) (P < 0.001) with values ranging from +26.6 to -13.9 ‰ prior to and during the El Nino evolution. The latter decrease in d-excess can be partly explained by an enhanced moisture flux convergence across the southeastern Caribbean Sea coupled with moisture transport from northern South America by means of an increased Caribbean Low Level Jet regime. During 2014-15, precipitation deficit across the Pacific domain averaged 46% resulting in a very severe drought; while a 94% precipitation surplus was observed in the Caribbean domain. Understanding these regional moisture transport mechanisms during a strong El Nino event may contribute to a) better understanding of precipitation anomalies in the tropics and b) re-evaluate past stable isotope interpretations of ENSO events in paleoclimatic archives within the Central America region. This article is protected by copyright. All rights reserved.

Isotope hydrology and baseflow geochemistry in natural and human-altered watersheds in the Inland Pacific Northwest, USA.

This study presents a stable isotope hydrology and geochemical analysis in the inland Pacific Northwest (PNW) of the USA. Isotope ratios were used to estimate mean transit times (MTTs) in natural and human-altered watersheds using the FLOWPC program. Isotope ratios in precipitation resulted in a regional meteoric water line of δ2H = 7.42·δ18O + 0.88 (n = 316; r2 = 0.97). Isotope compositions exhibited a strong temperature-dependent seasonality. Despite this seasonal variation, the stream δ18O variation was small. A significant regression (τ = 0.11D−1.09; r2 = 0.83) between baseflow MTTs and the damping ratio was found. Baseflow MTTs ranged from 0.4 to 0.6 years (human-altered), 0.7 to 1.7 years (mining-altered), and 0.7 to 3.2 years (forested). Greater MTTs were represented by more homogenous aqueous chemistry whereas smaller MTTs resulted in more dynamic compositions. The isotope and geochemical data presented provide a baseline for future hydrological modelling in the inland PNW.

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

ABSTRACT 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.

Methane Dynamics in a Tropical Serpentinizing Environment: The Santa Elena Ophiolite, Costa Rica

Uplifted ultramafic rocks represent an important vector for the transfer of carbon and reducing power from the deep subsurface into the biosphere and potentially support microbial life through serpentinization. This process has a strong influence upon the production of hydrogen and methane, which can be subsequently consumed by microbial communities. The Santa Elena Ophiolite (SEO) on the northwestern Pacific coast of Costa Rica comprises ~250 km2 of ultramafic rocks and mafic associations. The climatic conditions, consisting of strongly contrasting wet and dry seasons, make the SEO a unique hydrogeological setting, where water-rock reactions are enhanced by large storm events (up to 200 mm in a single storm). Previous work on hyperalkaline spring fluids collected within the SEO has identified the presence of microorganisms potentially involved in hydrogen, methane, and methanol oxidation (such as Hydrogenophaga, Methylobacterium, and Methylibium spp., respectively), as well as the presence of methanogenic Archaea (such as Methanobacterium). Similar organisms have also been documented at other serpentinizing sites, however their functions have not been confirmed. SEOs hyperalkaline springs have elevated methane concentrations, ranging from 145 to 900 μM, in comparison to the background concentrations (<0.3 μM). The presence and potential activity of microorganisms involved in methane cycling in serpentinization-influenced fluids from different sites within the SEO were investigated using molecular, geochemical, and modeling approaches. These results were combined to elucidate the bioenergetically favorable methane production and/or oxidation reactions in this tropical serpentinizing environment. The hyperalkaline springs at SEO contain a greater proportion of Archaea and methanogens than has been detected in any terrestrial serpentinizing system. Archaea involved in methanogenesis and anaerobic methane oxidation accounted from 40 to 90% of total archaeal sequences. Genes involved in methanogenic metabolisms were detected from the metagenome of one of the alkaline springs. Methanogenic activities are likely to be facilitated by the movement of nutrients, including dissolved inorganic carbon (DIC), from surface water and their infiltration into serpentinizing groundwater. These data provide new insight into methane cycle in tropical serpentinizing environments.

Hydroclimatic and ecohydrological resistance/resilience conditions across tropical biomes of Costa Rica

Water resources management in the tropics is challenged by climate variability and unregulated land use change and their impacts on the complex interactions between vegetation, soil, and atmosphere. This study focuses on the analysis of hydroclimatic and ecohydrological conditions across 6 major biomes in Costa Rica. Using the Budyko and the Tomer–Schilling frameworks, 31 reanalysis data points located across the Caribbean and Pacific domains were classified according to their ecohydrological resistance and resilience between 1989 and 2005. Observed data were used to evaluate the reanalysis products. Resistance was defined as the standard deviation in the water excess (Q/P), whereas resilience was defined as the standard deviation of the energy (AET/PET) to the water excess. A strong orographic separation was obtained between the water-limited Pacific slope and the energy-limited Caribbean slope. The Caribbean slope is characterized by low resistance and high resilience to changes in the hydroclimatic conditions, with small relative changes in water excess (−18% to 2.0%), whereas the Northern Pacific slope has high resistance and low resilience and exhibited strong changes in water excess (−34% to 0%). Some regions of the Northern Pacific region covered by lower and premontane forests have recently suffered significant increments in the dryness index (PET/P). This study demonstrates the need for national–regional strategies to effectively optimize water use efficiency and water storage and to include a climate vulnerability component in future water management plans.

Isotope hydrology of a tropical coffee agroforestry watershed: Seasonal and event-based analyses

Stable isotope variations are extremely useful for flow partitioning within the hydrologic cycle but remain poorly understood throughout the tropics, particularly in watersheds with rapidly infiltrating soils, such as Andisols in Central America. This study examines the fluctuations of stable isotope ratios (δ18O and δ2H) in the hydrologic components of a tropical coffee agroforestry watershed (~1 km2) with Andisol soils in Costa Rica. Samples were collected in precipitation, groundwater, springs, and stream water over 2 years. The local meteoric water line for the study site was δ2H = 8.5 δ18O + 18.02 (r2 = 0.97, n = 198). The isotope ratios in precipitation exhibited an enriched trend during the dry season and a notable depletion at the beginning of the wet season. The δ18O compositions in groundwater (average = −6.4‰, σ = 0.7) and stream water (average = −6.7‰, σ = 0.6) were relatively stable over time, and both components exhibited more enriched values in 2013, which was the drier year. No strong correlation was observed between the isotope ratios and the precipitation amount at the event or daily time‐step, but a correlation was observed on a monthly scale. Stream water and base flow hydrograph separations based on isotope end‐member estimations showed that pre‐event water originating from base flow was prevalent. However, isotope data indicate that event water originating from springs appears to have been the primary driver of initial rises in stream flow and peak flows. These results indicate that isotope sampling improves the understanding of water balance components, even in a tropical humid location, where significant variations in rainfall challenge current modelling efforts. Further research using fine‐scale hydrometric and isotopic data would enhance understanding the processes driving spring flow generation in watersheds.

Insight into the stable isotopic composition of glacial lakes in a tropical alpine ecosystem: Chirripó, Costa Rica

Stable Isotope Research Group, Chemistry Department, National University of Costa Rica, Heredia, Costa Rica Climatic Change and Climate Impacts, Institute for Environmental Sciences, University of Geneva, Geneva, Switzerland Dendrolab.ch, Institute for Environmental Sciences, University of Geneva, Geneva, Switzerland Departamento de Recursos Hídricos y Ciencias Ambientales y Facultad de Ingeniería, Universidad de Cuenca, Cuenca, Ecuador 5 Institute for Landscape Ecology and Resources Management (ILR), Research Centre for BioSystems, Land Use and Nutrition (IFZ), Justus Liebig University Giessen, Giessen, Germany Geography Department, University of Costa Rica, San José, Costa Rica Northern Rivers Institute, University of Aberdeen, Aberdeen, UK Civil and Environmental Engineering, Washington State University, Pullman, Washington Correspondence Germain Esquivel‐Hernández, Universidad Nacional de Costa Rica, Campus Omar Dengo, Heredia, Costa Rica. Email: germain.esquivel.hernandez@una.cr Funding information International Atomic Energy Agency, Grant/ Award Number: CRP‐19747; Research Office of the National University of Costa Rica, Grant/Award Numbers: SIA‐0101‐14 and SIA‐ 0482‐13; World Bank, Grant/Award Number: 8194‐CR‐UNA

Spatially distributed tracer-aided modelling to explore water and isotope transport, storage and mixing in a pristine, humid tropical catchment

Department of Geography, University of Costa Rica, San Pedro, Costa Rica 2 Institute of Environmental Engineering, ETH Zurich, Zurich, Switzerland Northern Rivers Institute, University of Aberdeen, Aberdeen, Scotland Department of Geography, Humboldt University Berlin, Berlin, Germany Department of Ecohydrology, IGB, Leibniz Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany Stable Isotope Research Laboratory, National University of Costa Rica, Heredia, Costa Rica Center for Geophysical Research, University of Costa Rica, San Pedro, Costa Rica Correspondence Christian Birkel, Department of Geography, University of Costa Rica, San Pedro, Costa Rica. Email: christian.birkel@ucr.ac.cr Funding information VEWA; UCR