Hydrogeochemical and environmental water quality standards in the overlap between high mountainous natural protected areas and copper mining activities (Mapocho river upper basin, Santiago, Chile)

Natural hydrogeochemical backgrounds or signatures from rivers around the world show great differences depending on the geological and hydrological settings where the specific watershed is placed. This fact is especially relevant and notorious, when the metallic content of waters draining hydrothermally-altered high-mountainous regions is considered. The present study offers a hydrogeochemical perspective to improve the generation of Environmental Water Quality Standards (EWQS) in mineralized high mountain regions comprised by rivers unaffected and affected by acid rock drainage (ARD). To this end, the complex and versatile reality at the Mapocho river upper basin (comprised by a natural ARD affected sub-basin, a mining intervened sub-basin and a third sub-basin with Andean unaffected waters) was used to evaluate the effect of seasonal and long-term climatic variations on hydrothermally-altered high-mountainous regions. In addition, 22 different environmental water quality standards (EWQS) from different countries around the globe were analyzed. This information was used to define what could be understood as an acceptable water quality for environmental use. Also, the obtained elemental concentration and physicochemical ranges were compared with the results obtained at the Mapocho upper basin to assess the importance of regional and local geochemical backgrounds on the generation of EWQS. As a result of this information generation, compilation, analyses and intercomparison, several recommendations to consider during the generation of EWQS at heterogenous high mountainous watersheds comprised by both ARD affected and unaffected sub basins were made. Special attention was paid to the incorporation of seasonal variations and long-term effects (climate change) on the generation of more realistic and useful EWQS.