Integrating Experiments and Models To Unravel Interactions between Soil Organic Matter and Enhanced Weathering

Area of Science:

• Geochemistry
• Soil Science
• Environmental Science

Background:

• Predicting carbon sequestration via enhanced weathering (EW) faces uncertainties, especially concerning secondary mineral formation and organic matter interactions.
• Understanding these processes is crucial for developing effective carbon removal strategies.

Purpose of the Study:

• To compare a coupled inorganic-organic geochemical model (PHREEQCENTURY) with experimental data to assess carbon sequestration potential of EW.
• To investigate the effects of alkaline manure, basalt, and dunite amendments on soil geochemistry and CO2 efflux.

Main Methods:

• A 389-day mesocosm experiment with soils amended with alkaline manure, basalt, and dunite.
• Utilized PHREEQCENTURY geochemical modeling alongside soil measurements and CO2 efflux monitoring.
• Employed sequential extractions to analyze element retention.

Main Results:

• Silicate amendments did not increase dissolved inorganic carbon leaching or pedogenic carbonate accumulation.
• PHREEQC simulations showed base cations preferentially precipitated as secondary clays, inhibiting CO2 removal.
• Manure addition reduced basalt reactivity and likely inhibited weathering of primary silicate minerals.
• Soil CO2 efflux did not significantly differ among treatments, aligning with model predictions.

Conclusions:

• Enhanced weathering with tested amendments showed limited carbon sequestration potential in this soil system.
• Secondary clay formation and manure's counteractive effects on weathering limit EW efficacy.
• Geochemical modeling is valuable for predicting EW performance and identifying key biogeochemical limitations.