Hydrogeological research in the Ordesa and Monte Perdido National Park (Huesca, Spain)

Abstract

The National Park of Ordesa and Monte Perdido (PNOMP) is the largest mountainous limestone massif of Western Europe. It has the highest altitude karst of the whole Europe. Groundwater is essential for the genesis, development and evolution of the park. The spatial distribution of recharge infiltration capacity is obtained by using the APLIS method. Additionally, a preliminary estimation of recharge is obtained by using the HBV and Visual Balan codes. The values of average surface runoff, evapotranspiration and recharge for the whole Paleocene-Eocene aquifer in the park are respectively about 160, 360 and 1227 mm/yr, or 10, 20 and 70% of yearly precipitation. Average recharge ranges between 72 and 77% of yearly average precipitation. This highlights the high vulnerability of water resources of PNOMP to possible climate and global change, according to surface and deep karstification and the snow cover during several months a year. Water is mainly of the calcium bicarbonate and calcium-magnesium bicarbonate types. There is a dominant process of calcite dissolution, which is consistent with the carbonate nature of the most abundant materials in the park (Upper Cretaceous and Lower Paleocene Eocene). Other observed hydrogeochemical processes are anhydrite and/or gypsum dissolution, as well as a possible incongruent dissolution of dolomite in the Ordesa Valley. Water stable isotopes show that the fronts that produce the greatest precipitations come from the Atlantic Ocean. In autumn, winter and spring there is a deuterium excess in the recharge water which is assumed to be related with diurnal snow sublimation and night water vapour condensation over the snow pack. The recharge elevation zone is located between 1950 and 2600 m asl, and most of the sampled springs show short transit times, between 1 and 4 years, although one of the springs (Fuen dero Baño) shows the influence of a slowly changing regional groundwater flow system.