Characterization of the stable isotopic composition of precipitation, surface, and subsurface waters in a small Andean catchment in northern Ecuador

Abstract

Combining traditional hydrometric data with environmental tracers such as water stable isotopes has proven valuable to improve the understanding of catchment hydrology. Nevertheless, the application of isotopic tracers in headwater catchments of the tropical Andes remains limited. The stable isotopic composition of precipitation, soil water along two experimental hillslopes with different vegetation cover (tussock grass and cushion plants), wetlands, and discharge collected biweekly during one year was used to improve the understanding of the hydrology of a northern Ecuadorian paramo catchment. The analysis of the stable isotopic composition of precipitation indicates that although local precipitation forms under isotopic equilibrium conditions, it is influenced by moisture recycling processes. Regarding catchment hydrological behavior, the spatio-temporal variability of isotopic signals and the analysis of inverse transit time proxies (ITTPs) of surface (discharge) and subsurface (soil water and wetlands) waters suggest that vertical flow paths are dominant across the catchment. Strongly damped isotopic compositions of these waters further suggest a high water storage capacity of the catchment, increasing the transit time or age of water in the hydrological system. Isotopic signals and ITTPs also show the importance of well-mixed subsurface water reservoirs in the hydrology of the system. The hydrological knowledge developed in this study not only increases the understanding of discharge generation and regulation in northern Ecuadorian Paramos, but also can be used to improve the management of water resources in the region. Field restoration activities could be focused on trying to improve the catchment’s components that control its hydrology.