摘要：Diffusive–dispersive mass transfer is important for many groundwater quality problems as it drives the interaction between different reactants, thus influencing a wide variety of biogeochemical processes. In this study, we performed laboratory experiments to quantify O 2 transport in porous media, across the unsaturated–saturated interface, under both conservative and reactive transport conditions. As reactive system we considered the abiotic oxidation of Fe 2 in the presence of O 2 . We studied the reaction kinetics in batch experiments and its coupling with diffusive and dispersive transport processes by means of one-dimensional columns and two-dimensional flow-through experiments, respectively. A noninvasive optode technique was used to track O 2 transport into the initially anoxic porous medium at highly resolved spatial and temporal scales. The results show significant differences in the propagation of the conservative and reactive O 2 fronts. Under reactive conditions, O 2 , continuously provided from the atmosphere, was considerably retarded due to the interaction with dissolved Fe(II), initially present in the anoxic groundwater. The reaction between dissolved O 2 and Fe 2 led to the formation of an Fe(III) precipitation zone in the experiments. Reactive transport modeling based on a kinetic PHREEQC module tested in controlled batch experiments allowed a quantitative interpretation of the experimental results in both one- and two-dimensional setups.
