Snowmelt as a determinant factor in the hydrogeological behaviour of high mountain karst aquifers: The Garcés karst system, Central Pyrenees (Spain)

Time series of environmental tracers (groundwater stable isotope composition, electrical conductivity and temperature) and concentration breakthrough curves of artificial tracers (uranine, eosine, amino-G and naphtionate) have been analyzed to characterize fast preferential and slow matrix in-transit recharge flows in the Paleocene-Eocene limestone aquifer of the Ordesa and Monte Perdido National Park, an alpine karst system drained by a water table cave, a rare hydrological feature in high mountain karst systems with similar characteristics. Snowmelt favors the areal recharge of the system. This process is reflected in the large proportion of groundwater flowing through the connected porosity structure of the karst aquifer, which amounts the 75% of the total system water discharge. From the perspective of water resources recovery, the water capacity of the fissured-porous zone (matrix) represents 99% of the total karst system storage. The volume associated to the karst conduits is very small. The estimated mean travel times are 9 days for conduits and 475 days for connected porosity. These short travel times reveal high vulnerability of the karst system to pollutants in broad sense and a great impact of climate change on the associated water resources. [Display omitted] •The first hydrogeological characterization of the Garcés Karst system is presented.•Environmental and dye tracers are essential to study complex alpine karst aquifers.•The long presence of snow controls the hydrogeological system response.•Short travel times are plausible given the karstic nature of the aquifer system.•The karst system is highly vulnerable to pollutants and climate change impacts.