Simulation of soil water above a water table in a forested Spodosol
Phillips, L.P. | Comerford, N.B. | Neary, D.G. | Mansell, R.S.
The relationships between soil water potential and water table depth in the upper five horizons of an Ultic Haplaquod of the lower Coastal Plain flatwoods are described. Soil water pressure head in the E, Bh, Bs, and E' horizons was in hydrostatic equilibrium with the underlying water table during all conditions when water was perched above an argillic horizon. The A horizon was in equilibrium with the water tables only when water tables were less than 65 to 70 cm from the soil surface. Water pressure heads and contents in the soil profile were simulated using a finite-difference, one-dimensional, unsaturated water-flow model. Simulations of water pressure head were excellent for the lower horizons (E through E') under all conditions, and poor for the A horizon. During high water tables, water pressure head simulations for the A horizon were improved. Fewer discrepancies between measured and simulated conditions occur when water pressure head values are converted to volumetric water contents. Unfortunately, the water-flow model described here did not adequately handle high infiltration rate rainfall events experienced at the site. It is concluded that in these sandy soils: (i) water content is the preferred prediction variable; and (ii) further advances in mechanistically modeling water uptake from each soil horizon in forest ecosystems will be limited by adequate information on plant root biology.
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