Fluvial geochemistry in São Miguel Island (Azores, Portugal): Source and fluxes of inorganic solutes in an active volcanic environment

Higher solute fluxes are associated to HCO3 and Na, and the total CO2 flux is equal to 3647 t/yr in RRQ and 7546 t/yr in RRG. Mixture with thermal water discharges also influences river water chemistry and in RRQ the contribution to the annual average discharge rate was estimated in 2.96 × 106 m3/yr (12.8% of overall discharge rate in the watershed). In RRG thermal water discharges were estimated in 2.4 × 106 m3/yr (14.9% of the discharge rate). The minimum total CO2-consumption associated with low-temperature weathering is equal to 0.58 × 106 mol/km2/yr in Ribeira Quente river and equal to 0.78 × 106 mol/km2/yr in Ribeira Grande river.