What controls the hydrochemical compositions of mountainous river water in a glacierized catchment?

Abstract

AbstractChemical weathering processes has become a growing issue in research on carbon cycling, however, mineral weathering by sulfuric acid and carbonic acid and its possible impacts on carbon cycle are yet unknown over the typical glacial catchment. To investigate the mechanisms of mineral weathering processes and its influence, the spatial–temporal variations of the major ions in Mingyong River, a glacier‐originated river located on the southeastern edge of the Qinghai‐Tibetan Plateau, were investigated. The seasonal and spatial variations in river solutes were resulted from the hydrological conditions and different mineral weathering rates. The results showed that the major ion compositions of the river waters were characterized by the dominance of Ca2+, Mg2+, HCO3−, with a significantly rich in SO42−. A systematic increase in ionic concentrations (apart from NH4+ and NO3−) was observed in the river water from non‐monsoon to monsoon season as well as from upstream to downstream. Piper diagram results showed 100% (upstream‐midstream) and 72.5% (downstream) contributions to Ca‐HCO3 type, respectively, indicating that a dominated carbonate weathering to the river chemistry. The (Ca2++Mg2+)/HCO3− against (SO42−/HCO3−) scatter suggested that sulfuric and carbonic acid are responsible for chemical weathering. An increased contributions of sulfuric acid from upstream (43%) to downstream (87.3%) on the (Ca2++Mg2+) and from upstream (29.6%) to downstream (88.3%) on HCO3− using the stoichiometry analysis during the monsoon season. Contrarily, H2SO4‐related dissolution (>65%) processes controlled the carbonate weathering during the non‐monsoon season, which indicated that sulfuric acid played a significant part in the process of rock dissolution that intensifies weathering. The effects of accelerated weathering on drinking and irrigation suitability suggested that the Mingyong River water is subject to a salinity hazard. This research demonstrates that the weathering of catchments involving sulfuric acid has the potential to alter carbon cycle and should be considered in global carbon cycle models.