Farmers have long used cation-rich materials such as crushed limestone to improve
agricultural soils. Enhanced weathering (EW) builds on that familiar land-management
idea: By applying crushed cation-rich rocks or minerals to soils, especially croplands,
the materials can react with carbon dioxide and water, release useful cations and form
dissolved bicarbonate that moves through soil water, groundwater and rivers.
Dr. Shuang Zhang, assistant professor in the Department of Oceanography, was
awarded a National Science Foundation CAREER Award to study that land-to-river
pathway and develop new tools for quantifying carbon transport and transformation
following terrestrial enhanced weathering.
"Dr. Zhang is building the kind of interdisciplinary research program the CAREER Award
is designed to support,” said Dr. Shari Yvon-Lewis, head of the Department of
Oceanography. "His work links carbon-cycle science, river biogeochemistry and data
science in a way that will help both the EW community and the students he trains.”
Science Beyond the Field
Zhang's project aims to build a more complete understanding of the science behind enhanced weathering. EW has promise for improving soil properties and crop yield, capturing carbon dioxide and contributing climate benefits; his work asks how much captured carbon stays in the land-river pathway and how river processes change that accounting.
"EW is a promising way to improve soils while capturing carbon dioxide,” Zhang said. “My project asks what happens after those weathering products leave the field and enter river networks."
To accelerate natural weathering, enhanced weathering increases the reactive surface area of cation-rich rocks or minerals by grinding them finely and spreading them across land. In agricultural settings, those materials can also help neutralize soil acidity and supply cations that support crop growth.
The chemistry does not end at the edge of a field. Runoff, lateral flow and groundwater can carry EW products into streams and rivers, where carbon can be transported, transformed, stored or released depending on river chemistry, biology and hydrology.
Tracking Carbon Through River Systems
Zhang’s CAREER project focuses on understanding how carbon cycles through river systems following enhanced weathering. The research will measure the following key processes:
- Carbonate speciation: How carbon is stored and transformed in water
- Carbon degassing: The release of carbon dioxide from water into the atmosphere
- Carbonate precipitation: The formation of carbon-containing minerals in water
- Photosynthesis: The process by which plants and algae use carbon dioxide to grow
- Respiration and hyporheic zone exchange: The release and transformation of carbon through biological activity and water exchange between the river channel and surrounding sediments
Using his background in data science, geochemistry and river modeling, Zhang is developing the answer through a new dynamic river network model.
Zhang's NSF CAREER Award research proposal focuses on tracking carbon cycling dynamics in river networks following terrestrial enhanced weathering. The Mississippi-Atchafalaya River Basin will serve as a natural laboratory because decades of agricultural liming have left a long-term record of how cation-rich amendments influence river chemistry.
“Rivers are not passive pipes; they are very reactive pipes,” Zhang said. “A lot of processes happen in the river, so my proposal will couple hydrological science with this new emerging field of enhanced rock weathering to quantify how much carbon cycling in the river is changing due to enhanced weathering.”
The new river model will integrate national hydrography, river and groundwater chemistry, watershed and climate data, historical lime application records, machine learning and reactive transport principles. Terrestrial enhanced weathering will be simulated using a soil-reactive transport model, then routed through hydrological pathways and tracked through connected river segments.
By comparing historical liming practices with designed enhanced weathering deployment scenarios, the project will examine the following factors influence downstream carbon loss and net carbon capture:
- River network resolution: The level of detail used to model river systems
- Deployment location: Where enhanced weathering is applied
- Application rate: How much material is applied
- Feedstock type: The type of material used
The result will be a modeling framework that can help researchers, farmers, carbon- removal developers and other stakeholders understand where enhanced weathering can deliver soil, crop, carbon-capture and climate benefits while maintaining rigorous carbon accounting.
Training the Next Generation of Environmental Leaders
Zhang’s interest in enhanced weathering grew from his broader interest in carbon, which he explored as a graduate student in the Department of Earth & Planetary Sciences at Yale University. He continues to study the global carbon cycle using data science in the CArbon Cycle and Earth Environment (CACEE) Lab at Texas A&M.
“Carbon is fundamental everywhere: the atmosphere, land, soil and ocean,” he said. “The carbon capture field is new and promising; we still need a lot of support to enlarge this market.”
The NSF CAREER Award provides funding for early-career faculty with the potential to serve as academic role models through the advancement of research in their departments. Selection for the award is based on the performance of innovative research at the frontiers of science and community service demonstrated through scientific leadership, education or community outreach.
Zhang’s proposal outlines his plan to integrate this research into educational programs that inspire and train the next generation of STEM leaders in geoscience and data science. The data-driven lesson module and hands-on computational tools developed through this project will train students to apply data-driven approaches to environmental challenges.