Graduate Thesis Or Dissertation
 

Addressing Emerging Issues in Tropical Ecohydrology : A Combined Hydrometric and Isotopic Approach to Evaluate the Origin and Age of Water in a High-Elevation Tropical Ecosystem

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  • This thesis focuses on the identification of ecohydrological processes in nested system of catchments in a tropical alpine (the wet Andean páramo) ecosystem. We accomplish this by conducting a water stable isotopic characterization of water sources, an evaluation of the mean transit time (MTT) of streams waters, and the investigation of landscape features and hydrologic variables controlling MTT variability. We found that the interplay between the high storage capacity of the wet Andean páramo soils and the slope of the catchments are the dominant controls on the ecosystem‘s high regulation capacity. The MTT modeling indicated that the subsurface transport of water in the basin preferentially occurs in the high organic and porous páramo soils and that there is a relatively simple transition of rainfall water through the subsurface towards the streams. MTT of stream water is relatively short, likely related to relatively short flow paths of water. These results lead us to conclude that the hydrologic system of this tropical alpine biome is dominated by shallow subsurface flow. Correlation analysis between landscape features and the MTT of streams waters evidenced that the hydropedology and the geology of the site do not control MTT variability, and rather slope topographical indexes control the delivery of water during to the drainage network. The lack of correlation between the MTT of streams and hydrological response variables (runoff coefficient and specific discharge rates) indicate that neither water yield, nor streamflow rates control the time water resides subsurface in the páramo soils. Finally, we found that mean electrical conductivity appears to be a promising proxy of MTT variability of stream waters in the study site. The isotopic characterization and the MTT evaluation in the Zhurucay basin have provided process-based understanding of the previously poorly understood ecohydrology of tropical alpine ecosystems.
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