Fen Management Handbook - Scottish Natural Heritage

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Creating fen from raised bog
In some areas of the UK, removal of raised and blanket bog peat for
the horticultural industry has resulted in extensive areas of bare peat or
underlying mineral substrate. Where hydrological and hydrochemical
conditions (such as acidity of the soil or groundwater, depth of water
that can be achieved) are unsuitable for bog re-establishment, or the
costs are prohibitive, conversion to fen vegetation may be appropriate
(Meade & Wheeler 2007), even if only as a pre-cursor to the
development of raised bog habitat in the very long-term. Several highly
valued fens developed without any active human intervention on cut-over
or otherwise damaged bogs (e.g. Whitlaw Mosses SAC, Crymlyn Bog
SAC, parts of Thorne Moors SAC). Given the rarity of raised bog and
the lack of opportunities to create new habitat of this type, it is unlikely
that the maintenance of fen would be a long-term management objective
on such sites.
Middlemuir Moss,
Aberdeenshire, a cut
over bog showing slow
natural colonisation by
cotton-grass 15 years after
abandonment. Colonisation
by fen and bog plants could
be enhanced by raising
water levels across the
whole area. (A. McBride)
9.2 Benefits of fen creation - integration with flood risk management
Capacity of fens to store storm water and help reduce flooding downstream
depends on location in the catchment, and the area and depth to which the fen
can be flooded. Deliberate flooding with river water may in turn affect the type
of fen, depending on the depth and duration of flooding, time of year, nutrient
concentrations of any deposited sediment, and land management between floods.
Reedbed and associated tall herbaceous fen vegetation may develop on ungrazed
fens subject to deep and persistent periods of inundation. If the flooding is not too
deep and persistent, with low nutrient/silt loads, and there is light grazing between
floods, fen meadow is more likely. However, creation of herb-rich fens in areas
subject to seasonal flooding with eutrophic water is likely to be unsuccessful due to
high nutrient levels encouraging dominance by reed or reed sweet-grass (Glyceria
maxima).
Potential opportunities for fen creation may arise as part of sustainable urban
drainage schemes (SUDS) such as balancing ponds, set back of river defences
and flood storage schemes and washlands (land deliberately flooded to reduce the
risk of rivers over-topping). Although often small and of the commoner types of fen
vegetation, such schemes are nonetheless valuable. Most new washland creation
schemes for flood risk alleviation are unlikely to provide suitable conditions for the
creation of fen habitat (Morris et al. 2004), except where persistent groundwater or
surface water supplies can maintain permanently wet areas.