More for xela1 #8Last one
EXPERIMENTS WITH WATER INTRODUCED FROM ABOVE
In the natural environment water is introduced initially into a soil from above (rainfall). A limited number of experiments have been carried out in which controlled amounts of water were added from above. In this case, the silica sand was 'primed' with a solution containing the metals of interest, and allowed to dry before the simulated rainfall events were enacted. The lower well simply acted as a drainage sump and direct connection was severed. The daily surface recordings for two experiments in which 100 mm was added (a) in one event and (b) as 20 x 5 mm events, are shown in Figures 7.9(a-b) respectively.
Whilst the single high rainfall event in Figure 7.9(a) produced an initial diminution in signal (some liquid passed to the lower well), there was almost instant recovery upon drying of the surface. The overall signal for all elements was very similar to that produced for a much more even application of simulated rainfall as in Figure 7.9(b). Isolated high rainfall events do not destroy the A horizon signals. Metal is evidently able to return or recycle to the surface from deeper in the profile following passage of the high rainfall infiltration slug, compensating for the initial minor depletion which occurs. It is again worth recording that even in this case of 100 mm of simulated rainfall, greater than 80% of the applied water exited the profile from the top by evaporation. This mirrors the field-based calculations and observations of Chapter 2, where in Australia, most locations have the majority of water loss from the profile through the upper surface by evaporation. For metals contained in such pore fluids the net dominant direction of movement is upwards, and the zone of initial accumulation is where water is evaporated, i.e. near the surface.
Well, thats it, lessons over for the day
Owl