Geoscience Reference
In-Depth Information
Fig. 12.36 Concentrations
of a terbuthylazine and
b bromacil in the
experimental fields (5 core
samples, 400 cm depth) one
year after application of
chemicals and leaching with
110 cm of irrigation and
rainwater (Toiber-Yasur et al.
1999
)
Comparisons between the results obtained from the field-scale experiment and
the calculated bromacil concentrations using the ADE and MIM approaches
(0-200 cm depth) are presented in Fig.
12.38
. The analysis is restricted to char-
acterizing the measured bromacil concentration profiles expressed (in terms of
mass of soil) in terms of horizontal spatial averages at a given time. Both measured
and simulated concentration profiles demonstrate that the downward movement of
bromacil is limited by its adsorption to the soil. Russo et al. (
1998
) note that, for a
given flow regime, mass exchange between the mobile and immobile regions
retards bromacil degradation and affects the spatial distribution of bromacil. At
relatively large travel times, mass exchange also affects the spatial moments of the
distribution and increases the skewing of the bromacil breakthrough curves and the
prediction uncertainty, as compared to soils that contain only a single (mobile)
region. At relatively short travel times, both the ADE and MIM approaches yield
similar results. In the case of the Bet-Dagan field experiment, the transport of
bromacil under leaching is somewhat better described by the MIM than by the
ADE model. However, neither approach properly captures the complete profile.
