CONICET | Buscador de Institutos y Recursos Humanos

Water from the Mendoza River, in the North of Mendoza province (Argentina), derives mainly from glacier and snow melt. This river provides water for domestic use, irrigation, industry and hydroelectric energy generation. In these latitudes (32ºS), there are three mountain ranges with direction North-South, which receive different contributions of precipitation from Atlantic and Pacific moisture sources: from East to West, Precordillera, Cordillera Frontal, and Cordillera Principal. We propose that precipitation systems, and also geology and altitude differences in recharge areas, provide chemical and isotope signatures to the water from different basin areas, allowing the identification of the geographic and geologic origin of river water. With a temperature increase scenario and changes in precipitation regimes , it is important to differentiate and quantify the sources of river water, in order to manage water resources. The objective of this work is to obtain isotope and chemical tracers that allow us to distinguish different water sources which feed the different tributaries of the Mendoza river basin. We expected to find a characteristic stable isotope composition of the water originating in the Cordillera Principal, Cordillera Frontal and Precordillera, based on the different altitudes, temperatures, and moisture sources (Atlantic vs Pacific) of precipitation. We also expected to find different chemical signatures in water derived from snow, glacier melt, and groundwater. For this purpose, we collected water from precipitation, streams, groundwater, glacier ice, and snow in different time periods (February, May, and August 2011), with a total of 121 samples. The study area is located in the high basin area from the Mendoza River, from 1370 m a.s.l. in the entrance of the Potrerillos dam, to 4700 m a.s.l. in the Parque Provincial Aconcagua region. The chemical analyses to determine major ion concentrations and the stable isotope ratio δ18O were carried out in the Paul Scherrer Institut (PSI), Switzerland. According to the expectations, we found isotopic differences of streams originating in the different mountain ranges. δ18O values decreased from East to West, showing the lowest values in the Cordillera Principal region and the highest values in the Precordillera region, in agreement with altitude gradients and proposed differences of moisture sources (Atlantic vs Pacific). The chemical composition of surface waters also showed a distinct trend from West to East, from calcium and magnesium sulphate waters in the Cordillera Principal to calcium bicarbonate in the Frontal Cordillera. This evolution seems to reflect the geological features of the different mountain ranges. Summarizing, this study allows us to propose that it is possible to identify and quantify the contribution of precipitation from different geographic areas (Cordillera Principal, Cordillera Frontal and Precordillera) to the streams of the Mendoza river basin.