Fen Management Handbook - Scottish Natural Heritage

Case Study 4.1
Understanding Fen Nutrients: Biglands Bog
This 12 ha wetland site near Wigton in north Cumbria (grid reference NY258537)
has some attributes of basin mire but also has an axial stream and is best classified
as a floodplain fen. It lies within a shallow river valley on a bed of drift. Boulder
clay, alluvium and sand & gravel act as aquitards and aquifers respectively, so that
in the past, soligenous fen has developed on groundwater seepages along the
edge, topogenous fen has developed on the floodplain of the beck and small areas
composed of ombrotrophic peat have developed over a deep basin and where the
fen has been isolated from the main water flow. Records from the 1950s show that
the groundwater-fed fen supported species associated with base-rich conditions
such as the moss Scorpidium scorpioides, and with the ombrotrophic mires, these
were the main interests of the site.
In more recent times, the groundwater-fed fen vegetation has been lost. The
floodplain fen has taken over in all but the ombrotrophic areas, which are thought
to float and remain just a little higher than the flood waters. The beck catchment
is now largely arable; it carries discharge from a sewage works and much silt. The
consequence from flooding several times a year has been a build-up of nutrientenriched
silt and the spread of enriched surface water over most of the site. This is
thought to be responsible for the massive expansion of S28 Phalaris arundinacea
tall herb fen.
The fact that change has occurred is supported by the stratigraphic studies of
Wheeler and Wells (1989). In their description of one of the bores taken on the
western edge “The uppermost horizons were largely obscured by a thick alluvial
deposit (and associated Phalaris rhizomes) but immediately below this (40 cm
depth) the peat contained rather little wood and was apparently deposited in rather
wet circumstances with rafts of Scorpidium and some rather more base-tolerant
Sphagna. This may indicate a ‘flooding’ horizon upon more solid, woody peat.”
Biglands Bog illustrates how vulnerable some types of fen can be to land-use
changes and that any prospect of reversal involves fundamental changes in
catchment and surface water management.
M4 Carex rostrata-Sphagnum recurvum mire
M9 Carex rostrata-Calliergon cuspidatum/
giganteum mire
M18 Erica tetralix-Sphagnum papillosum raised & blanket mire
M27a M27 Filipendula ulmaria-Angelica sylvestris mire, Valeriana
officianalis-Rumex acetosa sub-community
M27b M27 Filipendula ulmaria-Angelica sylvestris mire, Urtica
dioica-Vicia cracca sub-community
S27a Carex rostrata-Potentilla palustris tall fen,
Carex rostrata-Equisetum fluviatile sub-community
S28 Phalaris arundinacea tall-herb fen
W3 Salix pentandra-Carex rostrata woodland.
W4 Betula pubescens-Molinia caerulea woodland
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