ISOTOPICAL AND HYDROCHEMICAL ANALISYS IN THE MENDOZA RIVER BASIN, CENTRAL ANDES OF ARGENTINA

CRESPO SEBASTIAN, GOMEZ LAURA, ARANIBAR JULIETA, BRUETSCH SABINA, SCHWIKOWSKI MARGIT

PSI_LCH_AnnualReport2011

PAUL SCHERRER INTITUT

Lugar: VILLIGEN; Año: 2012; p. 1 - 98

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 [1]. In these latitudes (32ºS), there are three mountain ranges with direction North-South. From East to West: Precordillera, Cordillera Frontal and Cordillera Principal. Given these features, it is possible to infer that geology, precipitation systems, and altitude differences in recharge areas have an influence on the chemical and isotope composition of the water in the different basin areas. With a temperature increase scenario and changes in the precipitation regimes [2], it is important to differentiate and quantify the recharge sources in the different areas in order to plan adaptation policies. The objective of this work is to obtain isotope and chemical tracers that allow us to distinguish different water sources which feed the different rivers of the Mendoza river basin. We expected to find a characteristic stable isotope composition of the water originating from 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 a different chemical fingerprint of the water originating from snow, glacier melting and groundwater. For this purpose, we collected water from streams, precipitation, 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  18O 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.  18O values decreased from East to West, showing the lowest values in the Cordillera Principal region and the highest values in the Precordillera region (Figure 1). The chemical composition of surface waters 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 (Figure 2). This evolution is assumed to reflect the geological features of the different mountain ranges. This study allows us to propose that it is possible to identify the contributions of different hydrologic components (glacier, snow, groundwater) and geographic areas (Cordillera Principal, Cordillera Frontal and Precordillera) to the streams of the Mendoza river basin.