Hydrochemical and isotopic evaluation of groundwater and river water in the transboundary Silala River watershed

This article reviews a hydro-chemical and isotopic study aiming to provide information about groundwater-surface water interactions in the Silala River, a transboundary basin shared between Chile and Bolivia. The chemical and isotopic data show: The springs located in the northern section of the lower course of the Silala River and the Cajones springs in Bolivia have similar characteristics and represent a shallow flow system feed by local recharge; In contrast, the springs located in the higher and southern sections of the lower course of the river have similar characteristics than the Orientales springs located in the higher part of river basin indicating these springs are associated with a high-altitude recharge area. The river in the upper course in Chile has similar chemical and isotopic characteristics to the springs already mentioned, indicating most of the river flow comes from the high part of the basin in Bolivia. The groundwater shows different chemical characteristics, similar depleted isotopic values, and much lower C-14 values (including Orientales groundwater) than the upper springs and river, providing the first evidence that both systems are not connected in the Chilean section of the river and the springs system is part of a perched aquifer confirmed by visual field observations. These data support a conceptual model which includes an interaction between a perched aquifer, probably in alluvial deposits on the flanks of the volcanoes, and the river as result of a complex system of fractures present in the near-surface levels of Silala Ignimbrite. This study provides valuable information for modeling of hydrological and hydrogeological data in the study area.This article is categorized under:Science of Water > Hydrological ProcessesScience of Water > Water Quality