Gas and solute reactive transport in variably saturated porous media

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The vadose zone, i.e. partially water saturated soils and sediments that extend from ground surface to the water table, constitutes a dynamic environment which receives water through infiltration of precipitation, exchanges gases with the atmosphere, and is affected by a range of geochemical and microbially mediated processes and plant-soil interactions. For example, organic contaminants, which have contacted soils through accidental spills, leaky underground storage tanks, or pipelines breaks, may be attenuated by enhanced biodegradation activity prior to contaminating the fully saturated groundwater zone. Similarly, the vadose zone can play an important role in the uptake and destruction of greenhouse gases from the atmosphere or from underlying anaerobic aquifers. On the other hand, soils and wetlands can significantly contribute to the production and emission of greenhouse gases. To understand these complex interactions and to predict contaminant attenuation and gas exchange with the atmosphere, it is necessary to consider the rhizosphere (i.e. the soil zone affected by plant roots), the vadose zone, and the saturated groundwater zone as an integrated system. Such an approach allows an evaluation of how vadose zone processes affect groundwater quality, and how transport and reaction processes in soils and wetlands affect the exchange of greenhouse gases with the atmosphere.