Assessing the deployment of enhanced rock weathering methods for carbon capture in pastureland

• Main Author: Seow, Sherryl Hui Shan
• Other Authors: Patrick Martin
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Agricultural Sciences; Earth and Environmental Sciences; Enhanced rock weathering; Climate change mitigation; Carbon dioxide removal; Dunite weathering
• Online Access: https://hdl.handle.net/10356/174819
• Institution: Nanyang Technological University

Enhanced weathering (EW) refers to the acceleration of chemical rock weathering as a carbon dioxide removal (CDR) method for climate change mitigation. Long-term field studies are needed to develop methods to monitor, report and verify CDR rates before EW can be deployed on a large scale. However, there are limited field trials globally and often only use basalt rock. Hence, our study aims to assess if CDR can be determined for another highly weatherable rock, dunite, through field trials across four pastureland sites in the Bay of Plenty, New Zealand. Dunite of two grain sizes was amended at rates of 40-100 t ha-1 across each site, and CDR rates were determined by the depletion of magnesium in the soil over time. Our initial sampling regime showed high variability in magnesium concentration measurements, which resulted in less accurate and precise CDR calculations. Therefore, we devised a second sampling regime to address spatial heterogeneity and natural variation in the soil. We sampled 20% more of the plot by volume, included replicates for statistical aggregation and homogenised the soil before collecting the samples. The improved sampling regime showed an average CDR of 1.47-12.77 t CO2 ha-1 y-1 across all application rates two years after the dunite amendment. Plots with fine-grained dunite had lower variability but no significant difference in CDR rate. We also observed added benefits to soil health as pH increased by 0.67±0.13 on average. However, nickel toxicity could be of concern at high dunite application rates and should be appropriately monitored and managed.