Soil porewater pH controls biogeochemical redox processes, adsorption, and mineral dissolution. However, many of the current biogeochemical models used to evaluate carbon cycling in organic-rich Arctic soils do not account for pH dynamics or pH buffering processes. While previous research evaluating carbon release from permafrost-affected soils has shown that anaerobic microbial transformation of soil organic carbon (SOC) can result in dramatic pH changes, there is still limited mechanistic representation of pH dynamics in present models. This is likely due to the lack of model representations linking proton transfer during biogeochemical cycling with pH buffering processes in soils. In this work, SOC proton-binding is quantitatively represented in PHREEQC with a selected suite of representative organic ligands, and model simulations are used to interpret titrations of organic iron-rich Arctic soil solutions from different environmental niches in northern Alaska. Soil titrations are supplemented with soil carbon extractions and aqueous and mineral-phase iron measurements. Further simulations incorporate iron mineral dissolution and precipitation, iron-SOC complexes, and explore the role of hydrous ferric oxide surface protonation. This work indicates that a simplified representation of SOC proton-binding equilibrium can be used to represent pH buffering in Arctic tundra soils. Future work focused on biogeochemical kinetic processes could incorporate this proposed proton-binding equilibrium scheme for a more robust representation of mechanistic relationships between microbial carbon degradation and soil water pH. Ultimately, these mechanistic models will improve predictions of carbon cycling in permafrost soils and lend insight into future warming-induced trends in CO<sub>2</sub> and CH<sub>4</sub> emissions in the Arctic.

Proton: Binding model to simulate pH buffering in Arctic tundra soils

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.