Monday, 28 October 2013

Cors Bodeilio on the fly!

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.  


Peat cutting at Cors Bodeilio to infill drainage ditches

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)

 





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