Water chemistry in Somún Cura region, Rio Negro and Chubut Provinces, Argentina

Abstract

The Somún Curá Magmatic Province it is conformed by volcanic and subvolcanic rocks and extends for 25.000 km2 at South centre of Río Negro Province and North centre of Chubut Province in Argentine Patagonia. The entire region under study belongs to a desert regime under extreme temperatures, -25°C in wintertime to 45°C in Summer time, with averages between 3°C to 35°C with very dry conditions. The rainy season is springtime with 50 mm to 225 mm/year. The evaporation/transpiration is higher than rains during all the year. Isotopically the water can be divided in four different groups, one for the north, one for the south with an Atlantic origin of precipitations and two small groups with a local signature (Parica et al. 2012; Parica et al. 2017; Remesal et al. 2017).If the rains are present in the system the main source of water are located in the high regions (Alta Sierra de Somún Curá, Apas, Talagapa, Sierra Negra de Telsen, etc) after snow melting, water transit occurs through the structures in the Plateau rocks forming. Some salinization may occur during this transit and increasing of temperatures too from upper to lower levels. Surface water is driven through streams, the most important are Valcheta (Rio Negro Province) and Telsen (Chubut Province). Into the basaltic plateau water circulation has place through the structures, from the upper levels by snow melting to lower levels, where the water get salts and temperatures (23° C for southern water outlets and 45°C for northern water outlets).Water chemistry have a narrow spread, the chemistry of water let to classify them into Calcium Chloride, Calcium Sulphate and Calcium Bicarbonate, with light salinization index, weak mineralization. No As was detected at the localities sampled, with pH between 7.4 to 8.4 these are mainly drinkable waters considering chemistry features and low salinization risks in soils (SAR index).