Influence of rainfall quantity on the isotopic composition (18O and 2H) of water in mountainous areas. Application for groundwater research in the Yunquera-Nieves karst aquifers (S Spain)

The isotopic composition (18O and 2H) of rainwater and groundwater was determined in the Yunquera-Nieves hydrogeological unit, a karstic massif in S Spain with complex orography and hydrogeology. The aims were to identify: (1) the source of the water, (2) the main factors determining the isotopic content, (3) the catchment area of the springs and (4) the aquifer behaviour. The isotopic content of the sampled waters is of mixed Atlantic–Mediterranean origin and is opposite to the quantity of rainwater distribution, both in space and time. Spatially, water is isotopically less depleted toward the eastern sector, where rainwater quantity is lower (which is locally affected by the orography): thus, it is possible to differentiate the catchment areas of the main springs. Aquifer recharge is produced by winter precipitation, when rainfall water is isotopically more negative and evaporation is lower. The decrease in rainfall quantity during the study period provoked an increase in δ18O and δ2H values, both in rainwater and in groundwater. The recorded variations of the isotopic content of the rainfall are rapidly evident in the spring waters, which demonstrates a well developed karst network inside the carbonate aquifers, and thus the existence of conduit flow systems.