Biogeochemical processes and reactive transport across environmental interfaces: From groundwater to soil

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Environmental interfaces can be defined as regions along which different compartments of the hydrologic system meet and interact. These compartments include aquifers - providing an important source for fresh groundwater, the unsaturated zone - containing soil gas in addition to water, soils - hosting a wide variety of plants, and the atmospheric boundary layer - consisting of the air we breathe and containing oxygen and carbon dioxide. Processes associated with these compartments are often studied in isolation. However, it is common that biogeochemical reactivity is highest at the interfaces between these compartments. In addition, it is important to understand mass fluxes across the boundaries, for example the exchange of greenhouse gases between soils and the atmosphere. Processes within these compartments and mass fluxes across interfaces play an important role in local, regional and global biogeochemical balances, affecting water quality, crop productivity, and atmospheric greenhouse gas concentrations. The overarching objective of my research program is the development of improved quantitative conceptual models for transport and biogeochemical reaction processes in shallow groundwater and soils, with a specific focus on mass transfer processes across environmental interfaces. My research program will make headway towards this long-term objective through a series of specific projects that all have in common the transfer of gases between compartments, including oxygen, carbon dioxide and methane. To this end, we will investigate the effect of accidental spills of ethanol-blended fuels in shallow unconfined aquifers by characterizing the spatial distribution and temporal evolution of soil gas and surficial gas emissions. We will investigate processes that control episodic methane gas migration at shale gas extraction sites and will develop and evaluate numerical modeling tools to characterize gas migration in aquifers, gas transfer to the unsaturated zone, and the fate of methane between water table and the ground surface. We will investigate whether we can use carbon dioxide effluxes to quantify greenhouse gas emissions from sulfide- and carbonate-rich mine waste and we will use carbon dioxide influx measurements to quantify in real time the carbon sequestration potential of ultra-mafic mine waste materials. In addition, we will work towards the development of an integrated numerical model suitable for simulating plant-soil interactions. This code will be applied to quantitatively assess bio-mineralization, i.e. the process of carbon sequestration by mineral trapping induced by plants, and interactions between plants and soil with effects on crop productivity and mineral weathering. Taken together, these studies will provide guidance towards best environmental management practices and will work towards breaking down interdisciplinary boundaries.