Impacts of anthropogenic activities on weathering and carbon fluxes: a case study in the Xijiang River basin, southwest China

Monthly hydrogeochemical and discharge values were collected in the middle and upper reaches of the Xijiang River basin from April 2011 to March 2012 for the purpose of assessing the impact of anthropogenic activities on geological carbon sinks. The results of this study show that (1) the main ions in river water were influenced by different natural conditions and anthropogenic activities; (2) in a hydrological year, weathering fluxes of dissolved inorganic carbon (DIC) were 50.00 × 10⁸, 1.52 × 10⁸, and 1.79 × 10⁸ kg CO₂ in the Wuzhou, Zhaoping, and Yangshuo transects, respectively; and furthermore, DIC_{carbonate acid} (carbon flux caused by carbonic acid) were 37.71 × 10⁸, 1.31 × 10⁸, and 1.56 × 10⁸ kg CO₂, respectively, which represents approximately 31.56, 10.15, and 15.29 g CO₂ m⁻² in the monitoring period; (3) the carbon flux from the participation of allogenic acid (such as sulfuric acid or nitric acid) in carbonate rock weathering was obvious, which must be eliminated from the calculation of the net carbon sink in carbonate rock weathering because it would be released into the atmosphere as a carbon source; and (4) in the geological processes, there was a clearly carbon sink loss caused by anthropogenic activities in various ways, which is attributed to the addition of nitric acid and sulfuric acid, such as through agricultural and industrial activities, and hydropower stations.