Unravelling the Role of Surface Water–Groundwater Connectivity in the Andean Páramo

The Andean páramo is a critical ecosystem for the regional downstream water supply. However, understanding the often-neglected role of groundwater in the páramo is challenging because of constraints on measuring at great depths within the bedrock. Drilling monitoring wells, collecting samples, and analyzing water and bedrock samples often require substantial economic resources. This study examines the connectivity between groundwater and surface water by integrating hydrometric and hydrochemical measurements from measured sources into a Bayesian mixing model. Results reveal that groundwater flows through bedrock fractures, contributing up to 12.3% of the total annual streamflow. Additionally, in terms of the contribution of groundwater to other hydrological units, groundwater accounts for 16%–41% of the water in springs and 37%–62% in Histosols. We also found that Histosols can be differentiated into groundwater-influenced Histosols, receiving water from below 20 m depth, and groundwater non-influenced Histosols, receiving contributions from hillslope flow. Groundwater appears to be crucial in regulating baseflow in the study catchment, accounting for up to 12.3% of streamflow at the catchment outlet via direct contribution during dry periods. Groundwater also sustains groundwater-fed Histosols and springs during dry periods, accounting for up to 62% and 41% of their total water mixture. Considering the contribution of groundwater-fed Histosols and springs to streamflow during dry periods, the total contribution of groundwater to streamflow results in 48.7%. Due to critically sustained baseflow during dry periods, a holistic understanding of the hydrological system, which includes both deep and shallow groundwater, is necessary to address the increasing water scarcity, prolonged droughts, and changing precipitation patterns.