Stanford University

*** Ph.D. Thesis/ Oral Defense ***

 

Mechanistic and Measurement Constraints on Soil Alkalinity Enhancement for Carbon Dioxide Removal

 

Brian Rogers

Tuesday, June 9, 2026, 9:30 AM

Green 365

Department of Earth System Science

Advisor: Dr. Kate Maher

Amending soils with alkaline minerals is a carbon dioxide removal (CDR) strategy that has received considerable scientific, commercial, and policy attention in recent years. Scaling this approach to atmospherically relevant levels, however, has been impeded by limited confidence in its measurability and durability. In this dissertation, I develop quantitative frameworks to evaluate whether soil alkalinity enhancement can produce measurable and durable CDR. First, I develop a probabilistic framework that represents spatial, analytical, and sampling uncertainty for a given measurement approach. Applied to solid-phase mass balance methods commonly proposed for CDR verification, this framework shows that spatial heterogeneity can make direct solid-phase verification prohibitively expensive at operational scales. Given these challenges in directly verifying feedstock dissolution, I then shift to mechanistically inferring the fate of alkalinity during transport through the soil column. I develop a thermodynamic framework that adapts classical agronomic concepts of soil buffering to the problem of enhanced alkalinity export. Because the framework is constrained by routine agronomic measurements, it enables standardized inference of soil buffering capacity across large areas and depth profiles. I use this approach to estimate depth-integrated soil alkalinity demand and show that substantial alkalinity is likely consumed before export occurs in acidic soils. I then embed this thermodynamic framework within a reactive transport model to evaluate the coupled effects of transport and buffering processes on alkalinity export. These simulations show that alkalinity is likely to be fully attenuated before reaching export depths over near-term project timescales in many acidic soils, and that a significant fraction of this attenuation can be attributed to secondary mineral precipitation in soils with even modest exchangeable aluminum. This finding complicates recent accounting frameworks that treat some forms of alkalinity loss as reversible, with important implications for CDR durability and crediting. Finally, I present global, mechanistically partitioned estimates of depth-integrated soil alkalinity demand and discuss the implications of these results for the future of carbon dioxide removal through soil alkalinity enhancement.