The dynamics of natural pipe hydrological behaviour in blanket peat

Natural soil pipes are found in peatlands, but little is known about their hydrological role. This paper presents the most complete set of pipe discharge data to date from a deep blanket peatland in Northern England. In a 17.4-ha catchment, we identified 24 perennially flowing and 60 ephemerally flowing pipe outlets. Eight pipe outlets along with the catchment outlet were continuously gauged over an 18-month period. The pipes in the catchment were estimated to produce around 13.7% of annual streamflow, with individual pipes often producing large peak flows (maximum peak of 3.8ls1). Almost all pipes, whether ephemerally or perennially flowing, shallow or deep (outlets>1m below the peat surface), showed increased discharge within a mean of 3h after rainfall commencement and were dominated by stormflow, indicating good connectivity between the peatland surface and the pipes. However, almost all pipes had a longer period between the hydrograph peak and the return to base flow compared with the stream (mean of 23.9h for pipes, 19.7h for stream). As a result, the proportion of streamflow produced by the pipes at any given time increased at low flows and formed the most important component of stream discharge for the lowest 10% of flows. Thus, a small number of perennially flowing pipes became more important to the stream system under low-flow conditions and probably received water via matrix flow during periods between storms. Given the importance of pipes to streamflow in blanket peatlands, further research is required into their wider role in influencing stream water chemistry, water temperature and fluvial carbon fluxes, as well as their role in altering local hydrochemical cycling within the peat mass itself. Enhanced piping within peatlands caused by environmental change may lead to changes in the streamflow regime with larger low flows and more prolonged drainage of the peat. Copyright (c) 2012 John Wiley & Sons, Ltd.