Lk. Heng et al., Anion and cation leaching through large undisturbed soil cores under different flow regimes. 2*. Simulation results, AUST J SOIL, 37(4), 1999, pp. 727-741
In the first part of this study, the movement of anions and cations during
sequential leaching of CaSO4 and KBr solutions under different flow regimes
in 2 large undisturbed cores was simulated using a mobile-immobile convect
ion-dispersion model (MIM). By using parameters from the literature or inde
pendently measured, and with 75% of the adsorption/exchange sites allocated
to the immobile water volume, the model was able to simulate the leaching
of bromide and sulfate in both cores, even when flow rates differed by more
than 2 orders of magnitude. The leaching of cations (Ca2+ and K+) in the s
low flow core, where cation exchange occurred, was also simulated reasonabl
y well. But the simulation of cation leaching in the fast flow core, where
the surface-applied solutes appeared very rapidly in the effluent, was poor
. Sensitivity analysis of the model output showed the most critical paramet
ers were the mobile water volume theta(m), the fraction of the adsorption s
ites associated with the mobile water f(s), and the mobile-immobile transfe
r coefficient alpha. Caution is needed when choosing these parameters for m
odelling purposes. The values used here gave good simulations of cation and
anion leaching at flow rates of 3-20 mm/h, but were not satisfactory at ve
ry high flow rates (350 mm/h).