Analyses and numerical evaluation of integrated time-series monitoring datasets including CO₂ concentration and fluxes at controlled CO₂ release site in South Korea

In Eumseong, Republic of Korea, a controlled CO₂ release site was designed by Korea CO₂ Storage Environmental Management (K-COSEM) Research Center to evaluate properly integrated CO₂ monitoring tools at the soil surface. CO₂ was released from the 55 m-length PVC-pipe buried at 2.5 m-depth, and then, CO₂ concentration and flux were monitored from August 1, 2015 to March 21, 2018 (965 days). Influencing environmental factors such as meteorological data, soil moisture and temperature at 5 different depths were monitored concurrently. The measured soil moisture content decreased rapidly when the soil temperature dropped below 0 °C. When CO₂ release began, both surface CO₂ flux and soil CO₂ concentration increased with a time lag. However, with occurrence of precipitation events, CO₂ flux decreased to almost 0 cm³ cm⁻² day⁻¹ but soil CO₂ concentration increased rapidly. The HYDRUS-SOILCO2 predicted soil moisture, temperature and natural background CO₂ flux compared to measured data (R² = 0.74, 0.89, and 0.85). The 10 scenarios were constructed with different soil characteristic curves. Unlike soil moisture content, the simulated natural CO₂ flux did not depend heavily on soil characteristics. The mass of released CO₂ was estimated by the difference between the measured CO₂ flux data during the release test and natural CO₂ prediction model. At the 2nd CO₂ release test, there was 1.5 times difference between the actual released CO₂ mass and calculated CO₂ mass.