Surface water quality in a sulfide mineral‐rich arid zone in North‐Central Chile: Learning from a complex past, addressing an uncertain future

Abstract

This study presents an analysis of up to 30 years of hydrological variables and selected water quality parameters (pH, SO4, Fe, Cu, and As) in the upper area of the Elqui River basin in North‐Central Chile. A correlation analysis determined statistically significant positive relationship for SO4‐Cu, Fe‐As, and Fe‐Cu. In terms of historical behaviour, no statistically significant trends were detected for precipitation or temperature. In contrast, for flow, there is an overall decreasing pattern for the entire area of study, although only in one case this trend was statistically significant. Along with the aforementioned analysis, a characterization of the flow‐water quality relationships is considered for the time period analyzed. Although erratic behaviours were confirmed, a negative (i.e., inverse) flow‐concentration relationship was identified for SO4, a positive (i.e., direct) relationship for Fe, and undefined relationships for As and Cu were obtained. From these analyses and based on previous studies on projections regarding climate change for the Andean region, and in particular for the upper Elqui zone, an estimation of the possible effects of the change in water regimes on water quality in the area of study is developed. It is likely that a decrease in surface flow, as a consequence of climate change could translate into improvements in water quality in terms of Fe and eventually As and Cu, but into an impairment in the case of SO4. In any case, this is a complex situation that demands special attention in the face of industrial activities that could be developed in tributaries like the Claro River, which currently play an important role in depurating or diluting contaminants in the waters of the Elqui River. Finally, it should be noted that this study addresses an issue that goes beyond the local interest and could be used as a reference to compare other transitional environments containing sulphide ores or areas of hydrothermal alterations, which are considered to be highly vulnerable to climate change and variability.

Drought impacts on water quality and potential implications for agricultural production in the Maipo River Basin, Central Chile

“…Only the station 6C showed a significant negative relationship with discharge. Similar positive correlations between Fe and discharge have been observed by Flores et al (2017) in the Elqui river basin in North Central Chile, but with a more erratic behaviour for Cu and As. It is expected that several elements from regular anthropogenic activities can concentrate due to limited dilution (Zwolsman and van Bokhoven 2007, Van Vliet and Zwolsman 2008).…”

“…This condition means that components sediment can be delivered with high flows (thaw streamflow) after a drought period, enhancing their concentration in the river. Flores et al (2017) suggested that turbulent flows associated with higher discharges could favour the transport of particulate forms of Fe in the Elqui basin. Furthermore, and according to Mosley et al (2014), in the acidification process resulted from sediment exposure to air during lower water levels, it can release high and potentially toxic concentrations of dissolved metals.…”

Guidance for the Integrated Use of Hydrological, Geochemical, and Isotopic Tools in Mining Operations

“…In addition to 'normal' seasonal variability of meteorological/hydrological processes (precipitation, surface discharges, groundwater levels), projected or expected climatic conditions should be considered when defining monitoring plans for compliance after closure. This precaution is necessary, because different parameters present different behaviours (in terms of concentrations) against discharge changes, as presented by Flores et al (2017) for a sulfide mineral-rich arid zone in north central Chile. Another study pointing out the effects of seasonal and climatic variations on mine sites with acid drainage is described by Nordstrom (2009).…”

Assessment of a conservative mixing model for the evaluation of constituent behavior below river confluences, Elqui River Basin, Chile

“…If appropriate, a simple approach, such as a conservative mixing model, would be especially useful for water managers who are not necessarily specialists in modeling issues, in situations when rapid assessments are required (e.g., torrential rain episodes flushing contaminants from the landscape; accidental releases and spills). Moreover, a simple scheme would be advantageous for the study (at least at an initial stage) of the possible effects of climate change on the hydrological response of rivers, and ultimately, related water quality issues (Byrne et al, 2020;Flores et al, 2017;Peña-Guerrero, Nauditt, Muñoz-Robles, Ribbe, & Meza, 2020).…”