, Volume 11, Issue 1-2, pp 65-83

Hydrological processes in abandoned and restored peatlands: An overview of management approaches

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Abstract

Mined peatlands do not readily recover their hydrological function, mainly because the dominant peat-forming plant genus, Sphagnum, cannot easily reestablish on the degraded surface peat found on cutover sites. Drainage and removal of the acrotelm can result in surface subsidence of up to3.7 cm y-1 m-1 of peat shortly after drainage (compression), and long-term rates up to 0.3 cm y-1 m-1 (compression and oxidation). This can decrease the hydraulic conductivity by over 75%, and decrease thewater retention capacity and specific yield. In old abandoned systems, drainage ditches may continue to facilitate a significant seasonal water loss.Colonization of abandoned sites by trees may increase the evapotranspirative losses by as much as 25%, and interception losses can be as high as 32% of rainfall. Without natural or planned occlusion of ditches, some peatlands become drier over time. Blocking ditches may largely restore water balance components, although the hydrological regime requires years to stabilise sufficiently for Sphagnum recolonization, especially where residualpeat is well decomposed, having inadequate water storage capacity. Consequently,winter precipitation (Europe) and spring snowmelt (North America) are criticalrecharge periods. Over the long term, consolidation of the peat due to drainageand methane production (where drainage systems are blocked and soils reflooded)decreases hydraulic conductivity, thereby reducing lateral seepage losses. This may actually assist in Sphagnum recolonization. A regenerated cover ofSphagnum increases soil wetness and reduces water tension (increases pore-water pressure) in the substrate, thus ameliorating its own environment. However, natural recolonization and recovery of many hydrological and ecological processes may not occur, or may require many decades. Water management and selective plant reintroduction can accelerate this. Water management options such as blocking ditches, constructing bunds, reconfiguring the surface and managing microclimate have met with varying degrees of success. No standard management prescription can be made because each site presents unique challenges.