Identification of the main sources of water that contribute to the generation of runoff in humid paramo Andean zones by using stable isotopes of water: deuterium (δ2H) and oxygen-18 (δ18O)

The hydrologic analysis of Andean páramo catchments is currently hindered by the limited existence of studies regarding the streamflow generation processes. To improve this situation and to provide a baseline for future hydrologic studies, an isotope fractionation analysis of deuterium (2H) and oxygen-18 (18O) was conducted on water samples collected biweekly between May 2011 and March 2012, within the Zhurucay river páramo micro-catchment (7,97 km2), located in the Ecuadorian austral region, between 3200 and 3800 m a.s.l. The monitoring points encompassed rainfall and runoff stations, and soil and spring water sampling points. Results reveal that pre-event water is the main source for streamflow generation during storm conditions, where the Histosols are the main contribution to the discharge. Andosols main function is to regulate runoff and recharge Histosols during normal conditions. The latter are recharged by virtue of their low-lying position in the landscape. During less humid conditions, results suggest that the Histosols are the main sources of discharge regulation. Similarly, there is no evidence of significant groundwater contribution to discharge.