Combining Traditional Hydrometric Data, Isotope Tracers and Biophysical Landscape Characteristics to Improve the Understanding of Landscape Hydrology in the Humid Andes

Abstract:

Only few catchments in the Andean mountain range are currently monitored. Most basins in the region remain ungauged, and as a result, little knowledge is available on the processes governing their hydrological behavior. In particular, despite the importance of tropical alpine grasslands of the northern Andes (commonly known as the páramo) as providers of abundant high-quality water for downstream populations as well as a variety of other environmental services, very little is known about their hydrologic functioning. To improve this situation, an analysis of 1) the isotopic signature of oxygen-18, and 2) the relations between various landscape attributes and hydrologic behavior in the Zhurucay River experimental catchment (7.53 km²) was conducted. The catchment is located in southern Ecuador between 3200 and 3900 m a.s.l. The isotopic analysis was conducted in water samples collected in rainfall, streamflow, and soils. The influence of soil type, vegetation cover, catchment area, geology, and topography on runoff coefficient, and streamflow rates was investigated using linear regression analysis. Results reveal that water yield accounts for a high percentage of the water budget; runoff coefficient, and high and moderate streamflow rates are highly correlated with the extent of Histosols soils (Andean páramo wetlands), and increase with catchment size; and low streamflow rates are highly correlated with steep slopes. Results from the tracer analysis show that pre-event water stored in the Histosols is the primary source of runoff generation, demonstrating hydrologic connectivity between the Histosols (mainly located at the bottom of the valley) and the drainage network; while the most common soils, the Andosols (mainly located on the steep slopes), laterally drain the infiltrated rainfall recharging the lower situated Histosols. Overall, these findings depict that the combination of different methodologies for investigating hydrological processes at catchment scale provides a more complete understanding of the ecosystem’s hydrologic functioning. Moreover, in developing regions, such as the Andean region, acquiring better understanding of the origin and fate of water is a critical step towards the establishment of scientifically-based programs of management and conservation of water resources.