Impact of Land Drainage on Peatland Hydrology

Abstract

There is a long history of drainage of blanket peat but few studies of the long-term hydrological impact of drainage. This paper aims to test differences in runoff production processes between intact and drained blanket peat catchments and determine whether there have been any long-term changes in stream flow since drainage occurred. Hillslope runoff processes and stream discharge were measured in four blanket peat catchments. Two catchments were drained with open-cut ditches in the 1950s. Ditching originally resulted in shorter lag times and flashier storm hydrographs but no change in the annual catchment runoff efficiency. In the period between 2002 and 2004, the hydrographs in the drained catchments, while still flashy, were less sensitive to rainfall than in the 1950s and the runoff efficiency had significantly increased. Drains resulted in a distinctive spatial pattern of runoff production across the slopes. Overland flow was significantly lower in the drained catchments where throughflow was more dominant. In the intact peatlands, matrix throughflow produced by peat layers below 10 cm was rare and produced <1% of the runoff. However, in drained peatlands, matrix throughflow in deeper peat layers was common and provided around 23% of the runoff from gauged plots. Macropore flow, the density of soil piping, and pipeflow were significantly greater in drained peatlands than in intact basins. Gradual changes to peat structure could explain the long-term changes in river flow, which are in addition to those occurring in the immediate aftermath of peatland drainage.

Hydrological Response of Alpine Wetlands to Climate Warming in the Eastern Tibetan Plateau

“…Moreover, as the WR and BR basins were both dug by similar ditch densities, i.e., 0.060 km¨km´2 and 0.066 km¨km´2, respectively [28,49], the similar ditching densities minimize potential impacts on differences between the WR and BR basins and cannot fully explain the observed hydrological differences between the two basins from 1985 to 2007. In addition, ditches can promote wetland drainage and thus result in more discharge if other hydrological conditions remain the same [50,51], but the in-situ hydrological records showed the contrary results in the two Zoige basins, i.e., decreasing trends in discharge.…”

Changing temperature and rainfall gradients in the British Uplands

“…It has been suggested that discharge is the major control of dissolved organic carbon fluxes from peatlands, which could explain a large proportion of recent increased flux estimates (Worrall et al 2003(Worrall et al , 2009. Similarly, it is likely that discharge acts as a crucial control on particulate carbon fluxes from upland peatlands, particularly in winter when peat may be more susceptible to loosening by freeze-thaw (Holden et al 2007a) and given that there are large areas of bare peat and open ditches with available sediment for mobilisation (Holden 2005, Holden et al 2006. However, this effect could be countered by a reduction in freeze-thaw activity associated with warmer conditions in the uplands and the likely impacts on fluvial export of carbon therefore require further research.…”

Hydrological behaviour of a drained agricultural peat catchment in the tropics. 1: Rainfall, runoff and water table relationships

“…Changes in hydrological properties, oxidation and subsidence, peat water acidity, peat fire, flooding and losses of freshwater supply are some of the potentially most negative environmental impacts commonly experienced in tropical peatlands due to drainage (Holden et al 2004, 2006, Worrall et al 2007, Langner and Siegert 2009). Chason and Siegel (1986) and Holden et al (2006) reported that reclamation, irrigation and drainage, road construction and other civil engineering activities disrupt the normal hydrology of peatlands. Watanabe et al (2009) and Sillins and Rothwell (1998) found that draining of a naturally shallow water table expedites the oxidation process of the peat materials and thus inevitably results in land subsidence.…”