Ecological Indicators (Jun 2023)
Influences of anthropogenic acids on carbonate weathering and CO2 sink in an agricultural karst wetland (South China)
Abstract
Carbonate minerals are the largest carbon (C) reservoir on earth. Quantitative assessment of carbonate weathering and CO2 sink flux caused by anthropogenic acids in karst wetland regions is imperative to improve understanding of the hydrogeochemical evolution and global C cycle in karst ecosystem. In this study, a typical field observation was conducted in the Huixian karst wetland (HKW) in South China. The hydrogeochemical and isotopic (δ15N-NO3–, δ18O-NO3–, and δ13CDIC) analyses combined with the MixSIAR model and stoichiometric coefficients were used to quantitatively estimate the influence of H2CO3, HNO3 and H2SO4 on carbonate weathering and CO2 sink flux. The results obtained showed that anthropogenic HNO3 and H2SO4 affect carbonate weathering in the HKW, evidenced by the significant correlations between hydrogeochemical parameters and δ13CDIC value. The quantitative results showed high contributions of HNO3 and H2SO4 to carbonate weathering in karst groundwater, with contribution ratio values of 20.91 ± 19.29 and 21.69 ± 26.88%, respectively. Besides karst water over-exploitation, this finding suggested that these anthropogenic acids were also an important cause of a decrease in ecological water levels, resulting in the shortage of karst water resource and degradation of wetland ecosystem. Moreover, the involvement of anthropogenic acids in the natural chemical weathering has significantly decreased the CO2 sink flux by 11.23 ± 7.94 and 41.60 ± 30.24% for surface water and groundwater, respectively, thereby potentially affecting the karst C cycle and global climate change. This present study provided an integrated quantitative approach for estimating the influence of H2CO3, HNO3, and H2SO4 on carbonate weathering and CO2 sink in karst wetland regions. Our study highlighted that the effects of anthropogenic acids on carbonate weathering need to be considered in future studies on the restoration of wetland ecosystems, particularly in intensive agricultural study areas.
