Macroporosity and infiltration in blanket peat: the implications of tension disc infiltrometer measurements

Little is known about the processes of infiltration and water movement in the upper layers of blanket peat. A tension infiltrometer was used to measure hydraulic conductivity in a blanket peat in the North Pennines, England. Measurements were taken from the surface down to 20 cm in depth for peat under four different vegetation covers. It was found that macropore flow is a significant pathway for water in the upper layers of this soil type. It was also found that peat depth and surface vegetation cover were associated with macroporosity and saturated hydraulic conductivity. The proportion of macropore flow was found to be greater at 5 cm depth than at 0, 10 and 20 cm depth. Peat beneath a Sphagnum cover tends to be more permeable and a greater proportion of macropore flow can occur beneath this vegetation type. Functional macroporosity and matrix flow in the near-surface layers of bare peat appear to have been affected by weathering processes. Comparision of results with rainfall records demonstrates that infiltration-excess overland flow is unlikely to be a common runoff-generating mechanism on blanket peat; rather, a saturation-excess mechanism combined with percolation-excess above much less permeable layers dominates the runoff response. Copyright  2001 John Wiley & Sons, Ltd.