Unveiling groundwater recharge elevations in a tropical Andean catchment: Insights from nine-year isotopic records

Abstract

Research on páramo ecosystems have demonstrated that groundwater contributions to baseflow are both permanent and substantial, particularly during periods of low rainfall. However, advancing this knowledge requires identifying the spatiotemporal variability of groundwater recharge in order to clarify the mechanisms that sustain baseflow. This study addresses this knowledge gap by identifying the groundwater recharge elevations and the temporal dynamics of groundwater recharge in the Quinuas Eco-hydrological Observatory, a páramo catchment located in Southern Ecuador. For this purpose, we utilized a unique nine-year dataset (2014-2023) of stable water isotopes ( 𝛿 18𝑂 ) and meteorological records. Groundwater recharge elevations were estimated by comparing 𝛿 18𝑂 in rainfall and groundwater samples collected across an altitudinal gradient (3218-4055 m a.s.l.). The temporal dynamics of recharge were assessed by applying cluster analysis to the groundwater isotope data and by estimating rainfall thresholds required to initiate recharge. Results indicate that groundwater recharge predominantly occurs above 4100 m a.s.l. Rainfall exceeding 110 mm per month is required to initiate effective recharge. Notably, this threshold corresponds to the most humid months of April and May (Cluster 1). These findings highlight the role of high-altitude zones in sustaining groundwater recharge and suggest that groundwater recharge is a near-continuous process throughout the year, except during dry months. This study underscores the utility of stable isotopes as powerful tools to understand the hydrological connectivity between rainfall and groundwater, provides essential insights for improving water resource management and conservation strategies in páramo ecosystems.