Groundwater Contribution to Alpine Ponds Recharge in Serra Da Estrela Natural Park, Portugal

Groundwater data from 15 springs at Serra da Estrela mountain, located at the Seia-Torre-Covilha sector, were collected between 2010 and 2011 along six fieldwork campaigns. Isotopic (2H; 18O, and 3H) and chemical determinations were performed. The data were compared with the isotopic and chemical composition of seven alpine ponds located within the same area. The local meteoric water line (δ2H = 6.58(±0.29) + 1.31(±1.23)) was calculated using groundwater isotopic data. The results show that the springs located at the highest altitudes are more depleted than those located downhill. A slightly different isotopic fractionation with altitude was found between the western and eastern slopes of Serra da Estrela Natural Park (0.12 ‰ versus 0.10 ‰ /100 m in δ18O, respectively). The groundwaters are hyposaline, mainly Cl-Na-type waters, with slightly acidic pH reflecting a shallow and short flow path and small residence time. The alpine ponds also show Cl-Na facies and are mainly recharged by direct precipitation. However, in two alpine ponds (L2 and L6), evidences for groundwater recharge were identified. The physical, chemical, and isotopic composition allowed the identification of: (i) contribution of de-icing into the groundwater and alpine ponds systems; (ii) contribution of the shallow groundwater flow toward the alpine ponds systems recharge.