Fen Management Handbook - Scottish Natural Heritage

inundation are less likely to be species-rich than those where the summer water
level is subsurface.
These ecohydrological guidelines provide only generic indications of water (and
nutrient) regime needs for wetland habitats, which vary from site to site because
of factors such as soil type, geology and climate. Hydrological guidelines for
species and habitats also tend to relate to ‘average’ conditions which are more
easily researched and defined than tolerance of less frequently experienced
hydrological events which may be critical to long-term maintenance of a habitat in
good condition. For example, low-frequency, high-magnitude flooding events are
required in certain wet woodland communities (e.g. NVC W6 Alnus glutinosa –
Urtica dioica woodland) to provide bare ground for seedlings to develop, which may
be essential to maintaining a healthy age distribution of trees.
Water supply mechanisms for a large number of wetland sites in England and
Wales have been identified as part of the Wetland Framework Project (Wheeler et
al 2009).
5.9 Compare existing and target regimes and identify necessary changes
Comparing the differences between existing and target fen type, hydrological
and nutrient regimes is the starting point in identifying changes necessary to
achieve agreed objectives. If the current regime matches the target regime, there
is no immediate need for intervention, but appropriate hydrological monitoring
(see Section 10: Monitoring to Inform Fen Management) and periodic review
is essential. Active management or intervention is required wherever there is a
disparity between existing and target regime(s).
5.10 Identify and assess viability of suitable techniques to achieve changes
A range of practical management techniques are outlined in Section 6: Fen
Vegetation Management, Section 7: Fen Water Management and Section 8:
Managing Fen Nutrient Enrichment. The case studies at the end of each of these
sections illustrate how these techniques have worked in practice, which will help
in assessing the suitability and viability of different techniques for a particular fen.
Even though the focus has usually been on a specific site, most of the case studies
have required some changes at a catchment scale. Some fens, such as the New
Forest Valley Mires experience similar problems over a very large area, and have
required landscape-scale solutions (see Case Study 7.1).
5.11 Sharing with agriculture
Groundwater-fed fens are often grouped over a single aquifer shared with
agricultural land. Agriculture may rely on irrigation from groundwater, which can
depress the water supply to the fen to a degree that causes habitat changes. A
typical example experienced at Cors Bodeilio Common, Anglesey, is the change
from the rare black-bog rush fen to the commoner blunt-flowered rush fen meadow,
with consequent significant reduction in plant diversity and loss of many rarer
species. One of the potential remedies could be to seek an alternative water supply
for agriculture but this could be costly and involves consideration of issues beyond
that of immediate fen management. Complications arise in that water-bearing rock
strata are often fractured, making it hard to predict connectivity within the aquifer,
and thus to demonstrate the impacts of abstraction on other sites such as wetlands
within the same catchment.
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