Kg. Villholth et al., FLOW AND TRANSPORT PROCESSES IN A MACROPOROUS SUBSURFACE-DRAINED GLACIAL TILL SOIL - I - FIELD INVESTIGATIONS, Journal of hydrology, 207(1-2), 1998, pp. 98-120
The qualitative and quantitative effects of macropore flow and transpo
rt in an agricultural subsurface-drained glacial till soil in eastern
Denmark have been investigated. Three controlled tracer experiments on
individual field plots (each approximately 1000 m(2)) were carried ou
t by surface application of the conservative chloride ion under differ
ent application conditions. The subsequent continuous long-term monito
ring of the rate and chloride concentration of the drainage discharge
represented an integrated and large-scale approach to the problem. In
addition, point-scale determination of macropore structure and hydraul
ic efficiency, using image analysis and tension infiltration, and of s
oil water content, level of groundwater table, and chloride content of
soil water within the soil profile yielded insights into small-scale
processes and their associated variability. Macropore how was evidence
d directly by the rapid (within 10 mm of water input) and abrupt chlor
ide breakthrough in the drainage water at 1.2 m depth in two of the tr
acer experiments. In the third experiment, the effect of macropore tra
nsport was obvious from the rapid and relatively deep penetration of t
he tracer into the soil profile. Dye infiltration experiments in the f
ield as well as in the laboratory supported the recognition of the dom
inant contribution of macropores to the infiltration and transport pro
cess. The soil matrix significantly influenced the tracer distribution
by acting as a source or sink for continuous solute exchange with the
macropores. An average field-determined active macroporosity constitu
ted 0.2% of the total porosity, or approximately 10% of the total macr
oporosity. (C) 1998 Elsevier Science B.V. All rights reserved.