HYDROGEOCHEMICAL CHARACTERIZATION AND QUALITY ASSESSMENT OF GROUNDWATER AND SURFACE WATER WITHIN THE SAJAMA NATIONAL PARK AND ITS AREAS OF INFLUENCE, BOLIVIAN ALTIPLANO

The Sajama National Park (SNP), surrounded by the Sajama, Parinacota, Pomerate, and Kunturiri glaciers, are important water reservoirs that provide ecosystem services and are highly sensitive to climate change. It is located in the central Bolivian Altiplano at an altitude of 3,860 to 4,184 m.a.s.l. The SNP is characterized by an average annual precipitation of approximately 320 mm. The SNP is a volcanic complex covered by rocks of the dacitic-andesitic composition of the Quaternary age (0.6 Ma) and Turco area contains a variety of host rock deposits of tertiary age, basaltic copper deposits and light-colored tuff beds. The main objective of this study was to understand the processes that control the hydrogeochemistry of surface and groundwater to reliably and quantitatively predict the probable changes in water quality. 132 water samples were taken from various sources; including springs, hot springs, river, wetland, and groundwater. Field measurements include determinations of temperature (T), pH, Ox-Red potential (ORP), electrical conductivity (EC) and total dissolved solids (TDS). Water samples were collected for analysis of anions, cations, and trace elements. The water bodies that contribute to hydrologic system shows variable temperatures (4.6 – 31.1°C) with a slightly alkaline pH (5.9 – 9.4). The salinity varies from 56 to 29680 µS/cm, with variable redox conditions. The surface waters were predominantly Na-Cl-HCO₃-type, while Na-Ca-Mg-HCO₃-type water dominated in groundwater, and Na-Mg-HCO₃-Cl type in hot springs. The concentration of dissolved As in natural water sources varied from 0.004 to 1900 μg/L, B from 28 to 11792 μg/L and Li from 0.019 to 2810 μg/L, where the 56% of As and 47.5% of B exceed the maximum limits of the drinking water guideline WHO. The predominance of the different water types is associated with the dissolution of Na- and Ca-silicate minerals, as well as the dissolution of dolomite and calcite in the surrounding rocks of the region. However, the important variation observed in the hydrochemical characteristics of the volcanic zones is mainly due to the variations of the volcanic rocks from dacitic to rhyolitic and ignimbritic composition due to the interaction with the water that the solubility of the different minerals as well as due to direct mixing with the Junthuma and Sajama rivers with geothermal waters in the Sajama region.