Cors Bodeilio another of the internationally important valley mire fen in the Anglesey fen SAC and Ramsar complex. The fen is famed for elusive and aptly named fly orchid.
Looking out South over Cors Bodeilio national nature reserve towards the peaks of Snowdonia in the backdrop
Geological history re-visited
Located in a shallow valley 5 km from the east coast of Anglesey, the fen covers an area of
55 hectares, smaller than Cors Goch and Cors Erddreiniog but similar in that
they are groundwater dependent peatlands set in a landscape of intensive
agricultural systems. In the figure below (Beamish and
Farr, 2013) show a conceptual model giving the geomorphology
of the Anglesey fen complex. At Bodeilio, on the middle right of the diagram, an aquifer fed spring at the north-east
corner of the site percolates though limestone bedrock to irrigate the fen with
calcium rich waters at 18 mg/l.
Cors Bodeilio is intersected by a main drain that splits the
fen into east and west sections akin to Cors Erddreiniog. The
network of drainage channels serve to intercept the natural spring outflows and
transport the calcium rich water into a nearby river and eventually to sea. These drainage channels and evidence of remnant peat cuttings on the fen serve to
threaten the quality and future functionality of the ecosystem.
Looking over to the slope where fly orchid spring emerges
at the north east corner of the site
Hydrological management of the fen
Set in a river valley basin, the fen is influenced by a
natural spring system and seepage face called fly orchid spring. The
calcium rich spring water was being intercepted by a drainage ditch and was
transported off the fen. A hydrological system needed to be implemented to allow
the calcium rich water to irrigate the fen. This came in the form of an
adjustable twin wall corrugated outflow U bend pipe, used to ensure water levels
were kept high in the channel, and consequently the fen. The adjustable pipe,
over engineered due to legal covenants protecting the neighboring land from
flooding can be lowered during heavy rainfall to lower the water levels and let
more water to escape via the ditch.
Adjustable twin wall corrugated outflow U bend pipe,
used to control water level and direction onto the fen
The water was then directed by the pipe onto the fen via a
subsurface flow constructed wetland with a permeable reactive barrier of
woodchip under gravel. This is important as it can function before plants can
take hold by providing a surface area for a biofilm of denitrifying bacteria to
allow the removal of excess nitrogen. Plastic hexagonal sheet piling was used to stop water leaching back into the drainage ditch.
Subsurface flow constructed treatment Wetland receiving the sping water and spreading it out across the fen via a gravel over woodchip channel.
Hexagonal sheet piling used to reduce water seepage into drainage channel
Any alteration in the water table was carefully considered
as to achieve a desirable height for fen restoration but not too high as to
flood out important bank dwelling invertebrate communities. Some of the ditches
were blocked using peat that had been taken from 30cm cuttings, any deeper and
wind fetch may result in a wave action and sedges, bog bean, stonewort,
bladderwort and brown mosses would not colonise as wished.
Grazing management
The LIFE project purchased additional fen, an unmanaged strip of land owned by neighboring landowners. The biomass was initially burnt then cut and taken by
a wetland harvester. Drainage ditches were re-opened in order to reduce the
effect of winter flooding on the fen by lowering the water table. One of the management
problems here is the land could not be grazed after cutting as it was too wet,
however the summer of 2012 was one of the wettest on record and may be partly
to blame. Management is on-going here to get the water levels in the right
place.
Cladium mariscus ( or great fen sedge) is one of the indicators of the calcareous fen habitat protected under Annex 1 of the habitats directive
The fen, impenetrable just 4 years ago is now grazed by Dexter cattle in order to open up the sward and encourage early successional species
rich communities to establish. If left
under-grazed, monocultures of Cladium mariscus can dominate forming a closed canopy and outcompeting other species for sunlight and nutrients.
Management is targeted to favour Alkaline fen at the edges of the fen where water discharges and M13 communities, typified by Schoenus nigricans favour. Calcareous fen habitat found towards the centre of the fen, away from the spings. The future management may see another burn in 10 years time, however there is a threat here just like at the other fen sites from of a lack of management due to limited resources after the EU grants seize.
Ecosystem services
Previously, the fen had been view of as an unappealing place to visit and one of its recorded uses was a fly tipping site. Since active management has been implemented there is an opportunity for local people to access the fen via a boardwalk and use it for recreational purposes such as walking. There are also interpretation boards and some open areas of water creating an opportunity for educational talks and school visits. Making good use of the boardwalk around the fen. Notice the delicate balance between improved pasture on the right and specially adapted fen vegetation on the left on the boardwalk
The Boring Bit
Location: Cors Bodeilio, Isle of Anglesey, Wales
Grid Ref: SH501744
Date: Thursday 10th October 2013
Weather: Dry but cloudy (80% cover)
Weather: Dry but cloudy (80% cover)
No comments:
Post a Comment