Quantifying the impacts of non-carbonic acid (NCA) stress on dissolved inorganic carbon (DIC) generation in the granitic-hosted watershed, Huangshan UNESCO Global Geopark, China

Abstract

To better understand the impacts of non-carbonic acid (NCAs, including sulfuric, nitric and organic acids) stress on DIC generation during chemical weathering, this study investigated the water chemistry and stable isotope composition (δ¹³C_DIC) from a granitic-hosted watershed at Huangshan UNESCO Global Geopark, China. The results show that the dissolved loads of the watershed are dominated by both silicate and carbonate weathering. As a region with greatly distributed acid soil and high occurrence of acid rain, the evolution of the dissolved loads and δ¹³C_DIC show that DIC generation in carbonate dissolution is promoted by H₂SO₄, reduced by HNO₃ and little disturbed by organic acids. The reduction is due to CO₂ release in carbonate weathering by strong nitric acid formed by nitrification in acid soil. New participating proportions of NCAs in rock weathering yielded by the multiple linear regressions between major ions, DIC and δ¹³C_DIC are introduced into calculations of DIC yields. The overestimated DIC yields by silicate and carbonate weathering by NCAs account for about 34% of total DIC yields calculated with the assumption that all carbonates and silicates are dissolved by H₂CO₃ alone during a year. The results imply that the modifications of DIC generation by NCAs, especially HNO₃ formed in acidic silicate soil, could consequently partly counterbalance the natural CO₂ sink in the granitic-host region.