Impact of Aggregate-scale Heterogeneity of Transport and Biogeochemical Processes on Selenium Mobility in Soil

Selenium (Se) plays a role of two-fold importance in the environment: Trace amounts are essential to animal and microorganism health, while toxicity rapidly ensues at elevated concentrations. Bioavailable Se oxyanions can be immobilized in nature by microbial reduction to solid, elemental Se. In structured soils, which are characterized by strong systematic heterogeneity at the mm-cm scale, mass transfer limitations arising from the existence of predominantly diffusive transport domains within soil aggregates are likely to affect Se reduction rates. Working with simplified experimental systems in conjunction with reactive transport modeling, we investigated the heterogeneity in microbial Se reduction within artificial soil aggregates and elucidated their driving factors. The overarching objective of this project was to determine how the combined effects of local variation in mass transfer and biogeochemical processes that operate from micron to cm scales govern the fate and transport of selenium in soils.