Lithological and hydrological controls on water composition: evaporite dissolution and glacial weathering in the south central Andes of Argentina (33°–34°S)

Lithological and hydrological influence on fluvial physical and chemical erosion was studied in a glacierized sedimentary basin with high evaporite presence. Suspended particulate matter (SPM), total dissolved solids (TDS) and major ion concentrations were analysed for 2 years of different hydrologic condition: (i) 2009–2010, Q = 100% average; and (ii) 2010–2011, Q = 60% average. Annual hydrograph was simple regime-type with one peak in summer related to snow melting. The intra-annual SPM and TDS variations were directly and inversely associated to Q, respectively. Snow chemistry showed continental influence (Na+/Ca2+ = 0.17), and atmospheric input of TDS was <1% of the total exported flux. River water was highly concentrated in Ca2+ and SO42− (~4 mmol l−1) and in Na+ and Cl− (~3 mmol l−1). Ca2+/SO42− and Na+/Cl− molar ratios were ~1 and related to Q, directly and inversely, respectively. Major ion relationships suggest that river chemistry is controlled by evaporite (gypsum and halite) dissolution having a summer input from sulfide oxidation and carbonate dissolution, and a winter input from subsurface flow loaded with silicate weathering products. This variation pattern resulted in nearly chemostatic behaviour for Ca+, Mg2+ and SO42−, whereas Na+, Cl− and SiO2 concentrations showed to be controlled by dilution/concentration processes. During the 2009–2010 hydrological year, the fluxes of water, SPM and TDS registered in the snow melting–high Q season were, respectively, 71%, 92% and 67% of the annual total, whereas for equal period in 2010–2011, 56% of water, 86% of SPM and 54% of TDS annual fluxes were registered. The SPM fluxes for 2009–2010 and 2010–2011 were 1.19 × 106 and 0.79 × 106 t year−1, whereas TDS fluxes were 0.68 × 106 and 0.55 × 106 t year−1, respectively. Export rates for 2009–2010 were 484 t km2 year−1 for SPM and 275 t km2 year−1 for TDS. These rates are higher than those observed in glacierized granite basins and in non-glacierized evaporite basins, suggesting a synergistic effect of lithology and glaciers on physical and chemical erosion. Copyright © 2014 John Wiley & Sons, Ltd.