Characteristics of soil CO 2 under different conditions and its influence on water chemical composition: an experimental and modeling study in the laboratory

The water quality of the rainwater is obviously different from that of the groundwater after it reaches the surface and passes through the vadose zone. This study aims to further evaluate and analyze how soil CO 2 changes under natural conditions, to provide a theoretical background for the establishment of CO 2 geological storage, and to provide a basis for the detection of CO 2 leakage in order to provide insights for expanding CO 2 research. The changes in soil CO 2 concentration under different conditions were simulated and analyzed by laboratory experiments, and the effects of CO 2 on water chemical composition were also analyzed. In this study, two experimental groups (vegetation group (V) and high-temperature sterilization group (R)) and one blank group (B) were established. The results showed that the CO 2 concentration in column R was the lowest, while that in column V was the highest. With rainfall infiltration, soil CO 2 concentration gradually increased. When the rainwater infiltrated to 215 cm, the CO 2 concentrations in the columns V, B, and R were 5100 mg·m −3 , 4450 mg·m −3 , and 32,000 mg·m −3 , respectively. At infiltration depths from 5 to 215 cm, the Na + , Ca 2+ , Mg 2+ , SO 4 2− , and HCO 3 − concentrations in columns V and B decreased, whereas they increased in soil column R. The simulation revealed that the CO 2 concentration ranged from 560 mg·m −3 to 50,000 mg·m −3 ; pH value decreased; NO 3 − and Cl − remained stable; SO 4 2− decreased; and fCO 2 , HCO 3 − , Ca 2+ and Mg 2+ increased.