Simulating vertical flow in large peatlands

Ground-water flow simulations are used to evaluate the importance of three parameters on vertical flow in peatlands: regional slope. permeability of t he mineral soil underlying the peat, and peatland topography. Our results i ndicate that the extent of vertical ground-water flow in peatlands is prima rily controlled by mineral soil permeability. Local ground-water flow cells that form under small water-table mounds at bog domes can drive peat pore water into permeable mineral soil. However, when peat forms over low permea bility mineral soil, vertical movement of peat pore water becomes negligibl e and lateral flow of water in the upper portion of the peat column dominat es the peatland hydrology. This effect is not due to the low permeability o f humified peat layers, as is commonly assumed in many peatland studies. Fi eld data from the Hudson Bay Lowland (Canada) and the Glacial Lake Agassiz peatlands of northern Minnesota confirm the validity of these models. These results are relevant in settings other than peatlands where relief is low and small topographic mounds exist. (C) 2000 Elsevier Science B.V. All righ ts reserved.