Artificial drainage of peatlands: hydrological and hydrochemical process and wetland restoration

Abstract

Peatlands have been subject to artificial drainage for centuries. This drainage has been in response to agricultural demand, forestry, horticultural and energy properties of peat and alleviation of flood risk. However, the are several environmental problems associated with drainage of peatlands. This paper describes the nature of these problems and examines the evidence for changes in hydrological and hydrochemical processes associated with these changes. Traditional black-box water balance approaches demonstrate little about wetland dynamics and therefore the science of catchment response to peat drainage is poorly understood. It is crucial that a more process-based approach be adopted within peatland ecosystems. The environmental problems associated with peat drainage have led, in part, to a recent reversal in attitudes to peatlands and we have seen a move towards wetland restoration.However, a detailed understanding of hydrological, hydrochemical and ecological process-interactions will be fundamental if we are to adequately restore degraded peatlands, preserve those that are still intact and understand the impacts of such management actions at the catchment scale.Keywords: peat, moorland gripping, wetland restoration, water table, blanket peat, afforestation, drainage 2 I IntroductionPeat is decaying organic matter that has accumulated under saturated conditions. Formation of peat therefore occurs in areas of positive water balance. Peatlands are more likely to form in regions with high precipitation excess, such as upland areas of the temperate and boreal zones or in lowland areas where shallow gradients, impermeable substrates or topographic convergence maintain saturation.Classification of peatland types is generally related to two fundamental factors: source of nutrients and source of water. Bogs are ombrotrophic peatlands dependent on precipitation for water and nutrient supply, whereas minerotrophic peatlands or fens are reliant on groundwater for water and nutrient supply (Johnson and Dunham, 1963). Bogs are therefore highly acidic (pH < 4) and contain low amounts of calcium and magnesuim, whereas minertrophic peats are less acidic and tend to be base rich.In England and Wales peat is classified as a deposit of at least 30 cm depth (50 cm in Scotland) containing more than 50 % organic carbon (Johnson and Dunham, 1963).This definition is arbitrary as there is no clear break between a highly organic mineral soil (e.g. podzol) and an almost purely organic Sphagnum peat (Clymo, 1983).However, from this definition it is possible to say that 2.9 million ha or 13 % of Britain is covered in peat, most (2.6 million ha) of which is in Scotland (Milne and Brown, 1997). This represents less than 1 % of the 350 million ha of the northern peatlands that mainly occupy the boreal and subarctic zones (Gorham, 1991). In Britain the dominant peatland is blanket bog which occurs on the gentle slopes of upland plateaux, ridges and benches and is primarily supplied with water and nutrients in the form of precipitat...

Fighting carbon loss of degraded peatlands by jump-starting ecosystem functioning with ecological restoration

“…The effects of drainage on DOC have been controversial for a long time (see review by Holden et al 2004). Recent studies have found increased leaching and pore water concentrations of DOC soon after excavation of ditches (Wallage et al 2006; and drainage has been suggested to increase leaching of DOC to downstream watercourses (Huotari et al 2013).…”

“…pH and concentrations of several chemical elements increase in the pore and outflow water shortly after drainage , Moore et al 2013. In contrast, long-term changes of pore water chemistry after drainage are not well understood (Holden et al 2004). Drainage has also marked effects on peatland ecosystem structures like plant community composition , Mälson et al 2008).…”

“…In addition to short-term changes due to drainage , Holden et al 2004), chemical differences in pore water between pristine and drained sites can be observed still decades after drainage. There was also much larger variation in the water table level and water chemistry within the drained than the pristine sites.…”

“…Because of the lowered water table level, drainage increases aeration and promotes decomposition and nutrient mineralization in the peat matrix . Subsequently, pH and concentrations of several chemical elements increase in the pore and outflow water shortly after drainage Holden et al 2004;Moore et al 2013). In contrast, long-term changes of pore water chemistry after drainage are not well understood (Holden et al 2004).…”

“…Subsequently, pH and concentrations of several chemical elements increase in the pore and outflow water shortly after drainage Holden et al 2004;Moore et al 2013). In contrast, long-term changes of pore water chemistry after drainage are not well understood (Holden et al 2004). Indeed, understanding the changes in pore water, which is in direct contact to the peat, might help e.g.…”