The fates of CO2 generated by H2SO4 and/or HNO3 during the dissolution of carbonate and their influences on the karst-related carbon cycle

Abstract To distinguish the two fates of CO2 generated by H2SO4 and/or HNO3 during the dissolution of carbonate rock and to reveal the effect of this CO2 on the karst-related carbon cycle at short timescales, Baishuwan Spring (BSW; overlying secondary forest) and Lanhuagou Spring (LHG; overlying farmland) were monitored monthly by measurement of major elements and the stable carbon isotope of dissolved inorganic carbon (δ13CDIC) in spring water. The average net CO2 consumption, CO2 consumption by H2CO3, and CO2 emission by H2SO4 and/or HNO3 were 2.43, 2.65, and 0.23 mmol/L at BSW, whereas they were 1.07, 2.27, and 1.2 mmol/L at LHG, respectively. The low CO2 consumption by H2CO3 and the high CO2 emission by H2SO4 and/or HNO3 collectively led to a lower net CO2 consumption at LHG than at BSW; the effect of CO2 emissions was greater than the effect of CO2 consumption. The fates of the CO2 generated by H2SO4 and/or HNO3 were quantified. On average, 35.26% of this CO2 escaped from the water at BSW, whereas 82.82% escaped from the water at LHG, presumably due to different water-rock reaction times. Changes in the fate of CO2 may influence emissions and the karst-related carbon cycle.