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 + /Ca 2+  = 0.17), and atmospheric input of TDS was <1% of the total exported flux. River water was highly concentrated in Ca 2+ and SO 4 2− (~4 mmol l −1 ) and in Na + and Cl − (~3 mmol l −1 ). Ca 2+ /SO 4 2− 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 + , Mg 2+ and SO 4 2− , whereas Na + , Cl − and SiO 2 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 × 10 6 and 0.79 × 10 6  t year −1 , whereas TDS fluxes were 0.68 × 10 6 and 0.55 × 10 6  t year −1 , respectively. Export rates for 2009–2010 were 484 t km 2  year −1 for SPM and 275 t km 2  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.