The Effect of Potential CO2 Leakage from Carbon Capture and Storage (CCS) Site on Soil N2O and CH4 Emissions.

The CCS technology is to capture industrial CO₂ gas and store it in deep geological sites, which is an ultimate strategy to mitigate climate change. However, potential leakage of CO₂ is the main concern for this technology. Although a number of studies reported negative impacts of CO₂ leakage on plants, only a few studies have focused on soil microbial processes. To investigate the direct effect of CO2 on soil microbes, pure CO₂ was injected into the bottom of the chamber filled with 600ml of air-dried soil to have CO₂ and O₂ concentrations of 45(±5) % and 11(±2) %, respectively. The control chamber was also employed without CO₂ injection. Another set of CO₂ and control chambers were prepared and the soils were added with dicyandiamide (DCD) to further investigate soil nitrogen processes. The DCD is known as an effective inhibitor of nitrification and enabled us to investigate the source of N₂O production. The soil moisture was maintained at 60(±10) % water holding capacity and incubated for 120 hrs at 20(±1) ℃. Gas samples were collected after 3hrs, 72hrs and 120hrs of incubation. In the CO₂ chamber, N₂O flux after 3hrs was increased by 66.0% compared to the flux before injection, while the flux was not changed in control chamber. The DCD addition significantly reduced the amount of N₂O emission in the CO₂ chamber. This indicates that the increased N₂O emission by CO₂ injection might be originated from enhanced nitrification process. However, the increased N₂O emission did not last until 72hrs and rather, N₂O emission was decreased in the CO₂ chamber after 120 hrs even though extra N(NH₄Cl) was applied at 96 hrs. This indicates that enhanced nitrification by CO₂ injection only lasted very short term and prolonged CO₂ exposure inhibited nitrification. Soil NH₄⁺ and NO₃^- data further supported our speculation. On the other hand, overall CH₄ emissions were increased by 128.3% in the CO₂ chamber compared to control, indicating that soil environment became favorable for methanogenesis due to more anaerobic microsites. Our results showed that the effects of high soil CO₂ concentration on microbial processes are relatively rapid compared to that on plants and microbial community.