PEATLAND

Lowland raised bogs are peatland ecosystems which develop primarily in lowland areas such as the head of estuaries, along river flood plains and in topographic depressions. In such locations drainage may be impeded by a high groundwater table, or by low-permeability substrata. The resultant waterlogging provides anaerobic conditions which slow down the decomposition of plant material which in turn leads to an accumulation of peat. Continued accrual of peat elevates the bog surface above regional groundwater level to form a gently curving dome, from which the term ‘raised’ bog is derived. The thickness of the peat mantle varies considerably but can exceed 12 metres.

Lowland raised bogs may develop from a preceding phase of fen via successional processes or, if the climate is sufficiently wet, by peat formation directly onto a bare substrate, a process known as ‘paludification’. Accumulation of peat separates the bog surface from the influence of groundwater, so that it becomes irrigated exclusively by precipitation, giving rise to an ‘ombrotrophic’ bog. The raised bog surface may support a patterned surface of pools, hummocks and lawns, which provide a range of water regimes supporting different species assemblages, in particular, of Sphagnum mosses. Lowland raised bogs support a distinctive range of animals including a variety of breeding waders and wildfowl, and many rare and localised invertebrates.

Lowland raised bogs were once extensive habitats, formed in wet climatic phases in the flood plains of major rivers. In the region these habitats were a feature of the river systems at the base of the Pennine fringe, creating large areas such as those at Holcroft Moss and Risley Moss near Warrington, in the Mersey catchment, and a Lindow Moss, White Moss and Danes Moss, further south. Only small fragments of these original habitats remain, covering a total of 159ha.

Valley bogs and basin mires are distinctive features of a lowland glaciated landscape. A valley bog is distinguished by having an identifiable water flow as, for example, at Pettypool SSSI. A mire, however, develops where rainfall on the site is the only water supply. There is a significant group of such habitats in the Delamere complex, mostly remaining within the area of the forest managed by the Forestry Commission, including Abbots Moss SSSI. Many of the forest sites have been partially drained and planted with conifers earlier this century. The redevelopment of these areas as wetlands has already begun with Blakemere.

To the east of the Delamere complex there is a scattering of sites, including Wybunbury Moss, identified as a nationally important site. There is evidence that many sites were managed as local sources of peat into the 19th century. This habitat type is most at risk from drainage operations and nutrient enrichment.

An estimated 97% of lowland bogs in England and Wales have been damaged or destroyed. This is due to drainage for agricultural use, peat cutting for fuel in earlier times and extraction for horticultural peat. In Cheshire all areas of lowland raised bog have been disturbed to some extent, although a remnant of Holcroft Moss is thought never to have been cut. Thus conservation of remaining peatlands has become increasingly important, nationally and internationally.