Résumé :
|
The water content of porous media may substantially affect the transport behaviour of conservative and sorbing solutes. Physical processes potentially involved include alterations of the flow velocities, flow patterns, or of accessible surface sites. We performed column experiments using a synthetic porous medium, in which a substantial part of the sorption sites was concentrated in regions within small grained aggregates that were accessible only by diffusion, a feature often found in natural soils and sediments. We investigated the transport of solutes exhibiting very different sorption characteristics under steady state conditions at different water contents of the porous medium. The tracers used were either nonreactive, partitioned into organic matter or sorbed specifically and nonlinearly to clay minerals. Hydrodynamic dispersion generally increased with decreasing water content, reflected by the breakthrough curves (BTCs) of conservative and only slightly sorbing tracers, which exhibited stronger spreading and early breakthrough of the fronts at lower water saturation. Nonlinear sorption and nonequilibrium mass transfer between the mobile region and the immobile water present within the aggregates dominated the BTCs of the strongly sorbing tracer at all degrees of water saturation, and, thus, rendered the effects of increased hydrodynamic dispersion negligible.
|