5:15 PM - 7:15 PM
[AGE34-P10] Estimation of carbon fixation by basaltic rock application into the Japanese oxisol
Keywords:enhanced rock weathering, carbon fixation, column experiment
Technology to remove carbon dioxide (CO2) from the atmosphere is required to mitigate climate change. Enhanced rock weathering (ERW) focuses on reacting to silicate minerals with CO2 to dissolve as bicarbonate. Applying the crushed basaltic rocks to the croplands enhances the dissolution of the minerals, which captures atmospheric (soil) CO2.
Estimating carbon fixation is essential to evaluate the effectiveness of ERW and calculate carbon credits, but its methods have not been fully established. The main methods are to measure (1) the bicarbonate ion, (2) cations from mineral dissolution, and (3) the reduction of minerals. As comparative studies of their accuracy and effectiveness are lacking, this study compared three estimation methods through a soil column experiment with basaltic rock powder.
Kunigami marge collected in Okinawa Prefecture was used. Basalt was crushed to less than 100 µm in diameter. The soil and basalt powder (10% by weight of dry soil) were mixed and packed into the column (15 cm in inner diameter and 26 cm in height). Pure water was supplied from the top of the column every day at 5 mm hr-1 for three hours. The effluent was collected, and the pH, EC, major ions, and total inorganic carbon were measured. After the 30-day experiment, soil samples were taken from five soil layers, and the mineral content was determined using powdered X-ray diffraction.
The pH of the effluent was c.a. 1 higher than the soil pH, influenced by the basalt dissolution. The major cations were Na, Ca, and Mg, and Na concentration was 10 times higher than Mg and Ca ones. The major anions were the Cl ion in the early 10 days and the sulfate ion in the latter 20 days. Bicarbonate ions were kept around 0.2 mmol L-1, which was much lower than the other two anions. This is due to the low soil CO2 concentration (0.1%).
Carbon fixation was calculated to be 0.04 ton-CO2 ha-1 month-1 based on bicarbonate ion effluent. On the other hand, total anions were larger than cations, so we cannot calculate carbon fixation from the residue of the total cations and anions. This was due to the low bicarbonate level compared to the other anions. XRD result showed that basaltic rock has plagioclase as an easily dissolved mineral, and it was reduced by 34% in weight after the experiment. If all plagioclase reacted with CO2, carbon fixation would be 10.0 ton-CO2 ha-1 month-1, suggesting that only a small amount of the basalt would contribute to the carbon fixation in the acid soil with low CO2 concentration.
Estimating carbon fixation is essential to evaluate the effectiveness of ERW and calculate carbon credits, but its methods have not been fully established. The main methods are to measure (1) the bicarbonate ion, (2) cations from mineral dissolution, and (3) the reduction of minerals. As comparative studies of their accuracy and effectiveness are lacking, this study compared three estimation methods through a soil column experiment with basaltic rock powder.
Kunigami marge collected in Okinawa Prefecture was used. Basalt was crushed to less than 100 µm in diameter. The soil and basalt powder (10% by weight of dry soil) were mixed and packed into the column (15 cm in inner diameter and 26 cm in height). Pure water was supplied from the top of the column every day at 5 mm hr-1 for three hours. The effluent was collected, and the pH, EC, major ions, and total inorganic carbon were measured. After the 30-day experiment, soil samples were taken from five soil layers, and the mineral content was determined using powdered X-ray diffraction.
The pH of the effluent was c.a. 1 higher than the soil pH, influenced by the basalt dissolution. The major cations were Na, Ca, and Mg, and Na concentration was 10 times higher than Mg and Ca ones. The major anions were the Cl ion in the early 10 days and the sulfate ion in the latter 20 days. Bicarbonate ions were kept around 0.2 mmol L-1, which was much lower than the other two anions. This is due to the low soil CO2 concentration (0.1%).
Carbon fixation was calculated to be 0.04 ton-CO2 ha-1 month-1 based on bicarbonate ion effluent. On the other hand, total anions were larger than cations, so we cannot calculate carbon fixation from the residue of the total cations and anions. This was due to the low bicarbonate level compared to the other anions. XRD result showed that basaltic rock has plagioclase as an easily dissolved mineral, and it was reduced by 34% in weight after the experiment. If all plagioclase reacted with CO2, carbon fixation would be 10.0 ton-CO2 ha-1 month-1, suggesting that only a small amount of the basalt would contribute to the carbon fixation in the acid soil with low CO2 concentration.