CONVECTIVE-TRANSPORT OF CHEMICALS ACROSS A SEDIMENT-WATER INTERFACE

The transport of dissolved chemicals across a horizontal interface bet ween surface water and a saturated porous medium, associated with an u nstable density gradient across the interface, is studied experimental ly. Particular attention is paid to the starting conditions (i.e. the rate at which the density difference increases), and to the effect of changes in the density difference once the convective flow pattern has been established. The goal is a general flux law for any time variati on of the density difference. Three significant observations are discu ssed. First, greater masses added to the overlying water results in la rge? density instabilities that drive greater fluxes. Second, the rate of addition of the mass affects both the peak density gradient and th e long-term flux across the interface. Slower rates of addition result in greater variability in the resulting flux. Third, throughout all e xperiments, the ratios of final fluxes for different masses are simila r, regardless of addition time.