4. Research findings and applications
To our knowledge, CHRS is the only hydrological research site situated above the tree timberline (i.e., >3,000-3,100 m asl) in the Central American and Caribbean region. The Central American region is transected by a NW–SE mountain range that divides the region into the Caribbean and Pacific slopes with similar precipitation regimes (Sánchez-Murillo et al., 2020a). The unique geographic location of Costa Rica within this mountainous region, with moisture inputs from the Caribbean Sea (windward) and the Pacific Ocean (complex leeward topography), offers an ideal scenario for the use water stable isotopes to develop hydrological research (Sánchez-Murillo et al., 2020b).
Combined analysis of air mass back trajectories and the temporal precipitation isotopic variations for CHRS revealed the effective contribution of maritime moisture from the Caribbean Sea (90% frequency) and the Pacific Ocean (10% frequency), with the preferential contribution from the Caribbean due the influence of the north‐east trade winds travelling over the central and south‐eastern Caribbean Sea towards CHRS (Fig 2b,c; Esquivel-Hernández et al., 2019). CHRS data are also key to identify inputs from the central Pacific Ocean and local evapotranspiration fluxes. Overall, as water vapour encounters the main mountain range, orographic distillation and convergence increase, resulting in depleted precipitation arriving from the Pacific domain (Fig 2b; Sanchez-Murillo et al., 2020a). The lesser contribution of recycled water vapour arriving at CHRS is indicated by thed -excess variations in precipitation (d- excess values>10‰, Fig. 2c).
The first isotopic characterization of the surface water system of CHRS indicate that the evaporation conditions in the glacial lakes are highly influenced by input from precipitation that is in isotopic equilibrium with local water vapour, yielding low evaporation to inflow ratios (< 20%, Esquivel-Hernández et al., 2018). Due to their position near the equator and high elevation, lake water temperature of Lake Ditkevi shows seasonal variations but weak thermal stratification (Fig. 2a). Overall, the attenuation effect observed in the isotopic composition (δ18O) and d -excess of lake water most likely resulted from the relatively long residence times of precipitation, stream, and subsurface water (Fig. 2b,c). However, when compared to precipitation, lake and surface water reflects the evaporation effects as the corresponding evaporation lines (ELs) diverge from the local meteoric water line (LMWL) of the study region (Fig. 3). Therefore, because of the isotopic enrichment, the slopes of the ELs fall between the slope of the LMWL and the slope of local evaporation line (LEL) calculated using pan evaporation data (Fig.3; Esquivel-Hernández et al., 2018).
The intensity of sources or sinks of methane remain critically understudied in high elevation biomes and scarce data are currently available in the literature for the neotropical Páramo ecosystems. CHRS meteorological data were essential to identify key drivers of methane fluxes in soils of the Chirripó National Park. Overall, the identified soil and vegetation gradients revealed that sites without drainage-impeding soil layers or with the facilitating presence of vigorous Chusquea vegetation led to relatively stronger sinks of methane as compared to fields with wetter, less aerated soils (Chai et al., 2020). CHRS data has also served as baseline information to improve the limited paleoclimate data in Central America and to provide reliable estimates of hydroclimate and environmental change in this region (Wu et al., 2019a,b).