17:15 〜 19:15
[AGE34-P06] 玄武岩混合土壌からの玄武岩流亡の評価
キーワード：風化促進、二酸化炭素除去、水食、土壌流亡、X線回折
Carbon Dioxide Removal (CDR), which removes CO2 from the atmosphere, has been considered as a mitigation measure for global warming. One of the CDR methods is the enhanced weathering of basalt. When crushed basalt is mixed with soil, the reaction of basalt with atmospheric CO2 produces the bicarbonate. Either by entering groundwater as percolating water or by forming carbonates due to drying, CO2 is fixed in the soil. Basalt mixed with soil is expected to remain at the mixing site, and weather, but near-surface soil is washed away by surface runoff during rainfall events. The expected CDR may not be achieved if the eroded basalt enters a water body. Crushing basalt to be finer to accelerate weathering increases concerns about basalt loss since crushed basalt becomes highly erodible. In this study, we attempted to evaluate basalt loss from an Andisol mixed with basalt when subjected to rainfall.
Since it is impossible to identify sediments washed away by water erosion, attempts have been made to quantitatively discuss them using various tracers such as radioactive elements, rare earth elements, and magnetic properties of minerals. In this study, considering the significant difference in Plagioclase content between Andisol and crushed basalt, the full pattern summation of X-ray diffraction spectra, which has been conventionally used for quantitative evaluation of the mineral composition of rocks and other materials, was applied to the determination of mineral content in soil by the procedure in Kurokawa et al. (2024).
Andisol was mixed with 0, 10, and 20% crushed basalt with a grain size smaller than 0.1 mm and filled into a soil box with an 8% slope. Using a rainfall simulator, rainfall was applied at an intensity of 60 mm h-1 for 1 hour, and surface runoff and sediment samples were collected periodically at the downstream end.
After the rainfall, the mass of the eroded sediments, which had been oven-dried, was measured. Corundum (Al2O3) was then added as an internal standard, and the sample was subsequently crushed and dried. Diffraction spectra were obtained using an X-ray diffractometer (Miniflex 600, Rigaku), following the methodology outlined by Kurokawa et al. (2024). The mineral content of the sample was analyzed using the powdR software. A linear relationship was established between the basalt content and the plagioclase content in the Andisol, with a coefficient of determination of 0.98 obtained from the X-ray diffraction (XRD) data. This relationship was utilized to estimate the amount of basalt present in the eroded sediments. During rainfall events, soils containing 10% and 20% basalt resulted in sediment losses of 44 and 59 kg ha-1 for a runoff depth of 1 mm, respectively. This corresponds to basalt contents of 1.8 and 10.2 kg ha-1 for a runoff depth of 1 mm.
Assuming an annual rainfall of 1200 mm and an average runoff rate of 40%, the estimated annual basalt loss would be 0.86 t ha-1 and 4.9 t ha-1, respectively. This corresponds to approximately 1% and 2.7% of the amount of the basalt mixed into the soil when basalt is applied to the surface 15 cm thick soil layer.
This presentation is based on results obtained from a project (JPNP18016, Advanced Enhanced Rock Weathering (A-ERW) Technology Actively Combined With Site Characteristics) commissioned by the New Energy and Industrial Technology Development Organisation (NEDO). This work was also supported by JSPS KAKENHI (24K01867).
Since it is impossible to identify sediments washed away by water erosion, attempts have been made to quantitatively discuss them using various tracers such as radioactive elements, rare earth elements, and magnetic properties of minerals. In this study, considering the significant difference in Plagioclase content between Andisol and crushed basalt, the full pattern summation of X-ray diffraction spectra, which has been conventionally used for quantitative evaluation of the mineral composition of rocks and other materials, was applied to the determination of mineral content in soil by the procedure in Kurokawa et al. (2024).
Andisol was mixed with 0, 10, and 20% crushed basalt with a grain size smaller than 0.1 mm and filled into a soil box with an 8% slope. Using a rainfall simulator, rainfall was applied at an intensity of 60 mm h-1 for 1 hour, and surface runoff and sediment samples were collected periodically at the downstream end.
After the rainfall, the mass of the eroded sediments, which had been oven-dried, was measured. Corundum (Al2O3) was then added as an internal standard, and the sample was subsequently crushed and dried. Diffraction spectra were obtained using an X-ray diffractometer (Miniflex 600, Rigaku), following the methodology outlined by Kurokawa et al. (2024). The mineral content of the sample was analyzed using the powdR software. A linear relationship was established between the basalt content and the plagioclase content in the Andisol, with a coefficient of determination of 0.98 obtained from the X-ray diffraction (XRD) data. This relationship was utilized to estimate the amount of basalt present in the eroded sediments. During rainfall events, soils containing 10% and 20% basalt resulted in sediment losses of 44 and 59 kg ha-1 for a runoff depth of 1 mm, respectively. This corresponds to basalt contents of 1.8 and 10.2 kg ha-1 for a runoff depth of 1 mm.
Assuming an annual rainfall of 1200 mm and an average runoff rate of 40%, the estimated annual basalt loss would be 0.86 t ha-1 and 4.9 t ha-1, respectively. This corresponds to approximately 1% and 2.7% of the amount of the basalt mixed into the soil when basalt is applied to the surface 15 cm thick soil layer.
This presentation is based on results obtained from a project (JPNP18016, Advanced Enhanced Rock Weathering (A-ERW) Technology Actively Combined With Site Characteristics) commissioned by the New Energy and Industrial Technology Development Organisation (NEDO). This work was also supported by JSPS KAKENHI (24K01867).