Assessing Biogeochemical and Ecological Tradeoffs of Alkaline Waste-Based Carbon Removal

PI: Linta Reji
Co-Investigator: Manon Duret

Adding suitable alkaline mineral wastes, such as steel slag, to soils has been proposed as a promising strategy for open-systems carbon dioxide removal (CDR). However, slag can produce highly alkaline (pH > 10) runoff liquid that may harm soil ecosystems. Leveraging the CDR capacity of slag must therefore be carefully managed to balance net carbon removal with ecological health.

This project will use historical slag-affected wetland soil systems in the Calumet region of south Chicago as a natural, large-scale experiment to assess these tradeoffs and explore whether the CDR benefits of slag can be accessed without compromising ecological health.

Additionally, in highly alkaline soils (pH > 12) from the Calumet region, previous observations show a strong carbon dioxide uptake alongside a large methane release. The source of this methane is still unclear.

Understanding how these soils function will also support ongoing restoration efforts in the Calumet that aim to reduce soil pH toward more neutral levels and recover the area’s historical ecological integrity.

Two questions guide this research:

1. Does methane production under shifting redox conditions counteract the carbon dioxide removal achieved by slag amended soils?
2. Can soils be adjusted toward more neutral pH to restore ecological health while maintaining their carbon removal potential?

The research team will address these questions through a combination of field observations of total greenhouse gas fluxes and laboratory experiments that examine greenhouse gas balance across a range of soil pH conditions.