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 the mineral soil underlying the peat, and peatland topography. Our results indicate that the extent of vertical ground-water flow in peatlands is primarily 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 permeability mineral soil, vertical movement of peat pore water becomes negligible and lateral flow of water in the upper portion of the peat column dominates the peatland hydrology. This effect is not due to the low permeability of humified peat layers, as is commonly assumed in many peatland studies. Field 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.