Impact of manganese-driven redox processes on groundwater quality and soil carbon cycling

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The preservation of groundwater resources and the release of greenhouse gases represent critical environmental issues in Canada and worldwide. Soils play a central role in these challenges. The main goals of my research program in redox biogeochemistry are to understand groundwater contamination threats and to generate mechanistic understanding of mineral control on carbon sequestration in soils - the largest dynamic terrestrial carbon reservoir in the biosphere. By using a multidisciplinary approach, the proposed research program addresses two essential questions: (i) How do interactions among minerals (e.g., manganese oxides), microorganisms, and organic matter control redox-active geogenic contaminants which threaten groundwater quality? and (ii) What is the role of manganese oxides in soil carbon cycling? Manganese oxides are among the most reactive mineral phases in environmental systems and influence nearly every elemental cycle. Not only is Mn gaining recognition as an important control on both contaminant and carbon dynamics in aquatic and soil systems, but it is increasingly recognized as a contaminant of emerging concern in drinking water. The objective of this research program is to develop a better understanding of the dynamic cycling of Mn in soils, in order to provide safe drinking water and optimize carbon sequestration in soils. The proposed research addresses the following three axes: (1) Identifying physical and biogeochemical controls on Mn release in groundwater; (2) Evaluating competitive effect of Mn and C on geochemical processes controlling mobilization of geogenic As; and (3) Quantifying the abiotic transformation of complex organic C compounds by Mn oxides. The results will provide valuable information for the improved management of groundwater resources that are at risk of geogenic contamination. Surveying vital groundwater resources for native contaminants is critical to reduce public exposure and identify vulnerable areas for monitoring and management in order to prevent costly contaminant mobilization. In addition to helping allocate management resources more efficiently, the proposed research will provide valuable insight into controlling subsurface processes in order to minimize future groundwater contamination from natural sources. These results will provide water managers valuable information on whether aquifer geology or pedogenic and biogeochemical processes serve as better predictors of groundwater contamination. Finally, investigating the extent to which Mn oxides promote C mineralization will improve the accuracy of predicting how environmental changes and shifts in land-management may impact CO2 release. This improved understanding of mineral control on soil  cycling will be critical to ensure Canada reaches its 2030 emission reduction targets as committed to in the Paris agreement, especially in light of recent Québec legislation that calls for a complete ban of organic matter from landfills by 2020.