Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 10/20/1998
Publication Date: N/A
Technical Abstract: Soil hydraulic conductivity typically decreases dramatically as soil freezes, since pore water is replaced by ice. This is a cause of runoff and depressional ponding during spring snowmelt in regions where the underlying soil is frozen. Scientists in a number of locations have observed that ponds formed during snowmelt sometimes drain rapidly, before the soil profile has completely thawed. Field investigations of such phenomena in Minnesota have revealed the presence of isolated pockets of unfrozen soil, on the order of 1 m in diameter, within farm fields that otherwise still retain a frozen layer of 30 to 40 cm in thickness. These unfrozen zones have distinct, well-defined boundaries, and may serve as conduits for transport of meltwater. The cause of these features is unknown, but we propose that it may be due to surface heterogeneity in thermal admittance, which could induce lateral movement of water during the freezing process in nearly winter. This in turn would result in zones of "ice-poor" soil, with correspondingly higher air-filled porosity. Upon ponding in the spring these zones would exhibit higher hydraulic conductivity than the surrounding soil, and heat transport by infiltrating water would serve as a positive feedback, leading to preferential thaw. We have adapted an axisymmetric, finite element model of heat and water flow to test these hypotheses and perfomed sensitivity analyses, the results of which will be discussed.