Streamflow-concentration relationships of surface water in the Choapa basin: historical analysis and projections under climate change

The use of concentration-streamflow (C-Q) relationships is presented as a novel approach for studying climate change effects on water quality. Based on data from nine monitoring stations in the Choapa basin, north-central Chile, constituent behaviours were classified as constancy, enrichment or dilution. Constancy was shown for B, As, and Cu. Dilution and enrichment relationships were observed at some sites. Electrical conductivity and major ions showed dilution behaviour, with Na+, Mg2+, Cl-, SO4-2 and K+ showing greater variability in response to streamflow changes. Fe, Al, Mn and Zn presented enrichment behaviour, with Al and Fe showing greater variability. Based on historical C-Q relationships and available projections of streamflow variations under climate change, the change in constituent concentrations from 2010 to 2040 likely will not exceed +/- 10% with respect to the historical average, and +/- 15% from 2040 to 2070. In particular, Fe and Mn require special attention in the future.