The heterogeneity of the solute flux field in the horizontal plane at
the field scale has been documented in several field studies. On the o
ther hand, little information is available on the persistence of certa
in solute transport scenarios over consecutive infiltration cycles. Th
is study was initiated to analyse the recurrence of solute leaching be
haviour as estimated in two soil column tests emphasizing the preferen
tial flow phenomenon. Twenty-four small-sized soil samples were subjec
ted to two consecutive unsaturated steady-state flow leaching experime
nts with bromide as tracer. Observed breakthrough curves (BTCs) were a
nalysed by the method of moments and by the advection-dispersion equat
ion (ADE) to classify solute behaviour. Frequency distributions of the
parameters indicating the solute velocity were heavily skewed or bimo
dal, reflecting the broad variability of the leaching scenarios, inclu
ding some with pronounced preferential solute breakthrough. Exclusion
of the preferential flow columns from our calculations revealed an ave
rage amount of 37% of immobile water. The large-scale BTCs derived fro
m assembling the individual concentration courses of each run showed s
imilar features, such as an early bromide breakthrough. However, two d
istinct apices, viz. one preferential and one matrix, were observed on
ly in the first run, whereas the concentration decrease between the pe
aks was missing from the second run. A change in soil structure with c
ontinuous leaching was presumed to modify the interplay of the various
flow domains, thereby altering the spreading of the BTCs. Correlation
analysis between parameters of both tests suggests that preferential
transport conditions are likely to occur at the same locations in the
field over several infiltration cycles, whereas the 'classical' or exp
ected matrix flow is time variant and therefore seems to be hardly pre
dictable. (C) 1998 John Wiley & Sons, Ltd.