Citation:
I. P. Holman, I. G. Dubus, J. M. Hollis and C. D. Brown, Using a linked soil
model emulator and unsaturated zone leaching model to account for preferential
flow when assessing the spatially distributed risk of pesticide leaching to
groundwater in England and Wales, The Science of The Total Environment, Volume
318, Issues 1-3, 5 January 2004, Pages 73-88
Abstract:
Although macropore flow is recognized as an important process for the transport
of pesticides through a wide range of soils, none of the existing spatially
distributed methods for assessing the risk of pesticide leaching to groundwater
account for this phenomenon. The present paper presents a spatially distributed
modelling system for predicting pesticide losses to groundwater through micro-
and macropore flow paths. The system combines a meta version of the mechanistic,
dual porosity, preferential flow pesticide leaching model MACRO (the MACRO
emulator), which describes pesticide transport and attenuation in the soil zone,
to an attenuation factor leaching model for the unsaturated zone. The
development of the emulator was based on the results of over 4000 MACRO model
simulations. Model runs describe pesticide leaching for the range of soil types,
climate regimes, pesticide properties and application patterns in England and
Wales. Linking the MACRO emulator to existing spatial databases of soil, climate
and compound-specific loads allowed the prediction of the concentration of
pesticide leaching from the base of the soil profile (at 1 m depth) for a wide
range of pesticides. Attenuation and retardation of the pesticide during transit
through the unsaturated zone to the watertable was simulated using the substrate
attenuation factor model AQUAT. The MACRO emulator simulated pesticide loss in
10 of 12 lysimeter soil-pesticide combinations for which pesticide leaching was
shown to occur and also successfully predicted no loss from 3 soil-pesticide
combinations. Although the qualitative aspect of leaching was satisfactorily
predicted, actual pesticide concentrations in leachate were relatively poorly
predicted. At the national scale, the linked MACRO emulator / AQUAT system was
found to predict the relative order of, and realistic regional patterns of,
pesticide leaching for atrazine, isoproturon, chlorotoluron and lindane. The
methodology provides a first-step assessment of the potential for pesticide
leaching to groundwater in England and Wales. Further research is required to
improve the modelling concept proposed. The system can be used to refine
regional groundwater monitoring system designs and sampling strategies and
improve the cost-effectiveness of the measures needed to achieve “good status”
of groundwater quality as required by the Water Framework Direct
