Horses for Corsydd at Cors Erddreiniog

The second day of the Anglesey and Llyn fens LIFE conference saw a visit to another internationally important fen in East Anglesey! The story of the fen is a quite a contrast to that of the fen in my last Blog!

 

Looking south over Cors Erddreiniog from Nant Isaf, the 

Snowdonia mountian range in the backdrop. The spring heads at the 

eastern  egde of the fen are to the left of the frame.

Geological history revisited

Cors Erddreiniog is much like Cors Goch (see feature “a Fentastic day out”) in its origins as a glacial lake based on  the sandstone beds of the Carboniferous limestone series. The fen is under the ownership and management of Natural Resources Wales and is also designated as a SAC and ramsar site.

The fen was formed in much the same way as Cors Goch as a result of terrestrialisation of a glacial lake. The lake, called Llyn yr wyth eidion is subject to local folklore suggesting that its name came from a past farmer who upon ploughing his land with 8 Oxen, the animals for some reason bolted into the lake dragging the farmer with them. The only remaining artefact is an Ash branch that the farmer was holding onto and dug into the soil in a failed attempt to brake. The Ash tree is still visible near the lake today.

We began our walk from the eastern end of the fen just below the limestone springs at Nant Isaf farm. We are informed about the recent history and management of the site and how past drainage has had wider implications beyond the boundaries of the fen. 

Limestone scarps outcrop form the east forming three valley head springs and a diffuse groundwater seepage face that provide the valley basin with calcium-rich water akin to water source at Cors Goch.

 Conference party talking to the farmer at Cors Nant Isaf farm

Cause and effect of past management

In contrast to Cors Goch, this Wetland has been draining fairly efficiently in the past, owing to government pressure and subsidies paid to land owners to produce ever increasing amounts of food to meet the demand of modern society. The problem with this site in particular is that a network of drainage ditches were once intercepting some of the calcium rich spring water before it had chance to enter the fen. This valuable water was channelled into the main drain and eventually into a nearby river and finally out to sea. The problem here is multiple!

Firstly, when a Wetland is drained it loses the ability to store carbon within peat via a series of chemical reactions, and eventually loses this locked up carbon to the atmosphere as Carbon Dioxide gas. The second problem is that a drained peatland will start to waste away and cause a high concentration of dissolved organic carbon in the watercourse, making the water brown in colour. The third problem is that, prior to drainage, fen vegetation has the ability to form peat which can hold water throughout the year, this can lessen the impacts of winter flooding further downstream. 

Water Quantity and Water Quality

One of the spring heads being channelled into a drain.

The task of the LIFE project was to restore the hydrological pathways and allow the site to function as a peatland again. One of the keys to this was making time to create good links with the local landowners. The task of restoring the hydrological channels by re-routing some of the drainage ditches to by- pass the spring water, was made possible by building good relations with the surrounding landowners as most of the springs heads appear on neighbouring land.

 The neighbouring land where the spring heads 

are located. Notice the contrast between the green of the 

improved field and the brown fen of the fen vegetation.

 Here the LIFE project built a damn to cut off  the 

spring water from the enriched drainage channel.

  

  Enriched water is diverted into a drainage channel here

The spring water, through some light engineering and manipulation of drainage ditches, now seeps out onto the fen. Water from three different spring-head systems are now received either received directly by a constructed wetland or via a mixing chamber onto a constructed Wetland. This process acts to remove any excess nitrogen originating from fertiliser and pooling in an aquifer which may be elevating nitrate levels locally. The water was then received a bare peat scrape, via an infiltration trench. The scrape involved removing 40,000 tonnes of degraded peat to allow for re-colonisation by peat forming vegetation and kick-start peat accumulation once again.

Video courtesy of Natural Resources Wales. Peat stripping at Cae Gwyn to remove upper layers of nutrient enriched peat.

 

 Re-colonisation of sedges on the bare  scrape, The white matter is marl, which gives the scrape

 the welsh name Cae Gywn (White field)

Schoenus nigricans (Black bog-rush)  is a common feature of site. This is the constructed Wetland designed to receive a 7 litres/second discharge.

Shoenus nigricans (Black Bog Rush) is a common feature of the site.

The is the inspection chamber of the

infiltration trench.

The constrcuted Wetalnd has lead to a decrease in 

Nitrogen in the water from 24 at the inflow to 4 mg/l at the outflow

The mixing chamber and constructed wetlands were controlled by an outflow pipe where water could overflow during storm conditions. Excess water is firstly received by the infiltration trench untreated, then in cases of very high rainfall the excess was received by the drainage ditch.Plastic hexagonal sheet piling was sheet to separate the drainage ditch from the scrap to ensure that there was no seepage between the two to avoid. The scrape was carefully engineered on an east-west tilt to create a seepage that would naturally infiltrate the rest of the basin, for the same reason care was taken to to undercut the rest of the basin and the lake.  

Vegetation and grazing management.

A number of monitoring plots (10x10m with a 10m buffer) have been set up to assess the recolonisation of fen vegetation of the scrape, comparing different tecniques of re-vegetating using Black-bog rush Schonus nigricans seed heads, S. nigricans hay and a control.

  
Showing where the scrape ends and the cut vegetation begins. 

The grazing on the site is carried out by local farmers. The LIFE project offered free grazing and erected stock proof fencing to ensure livestock husbandry on the fen. The accounts of the local farmers have been positive, stocking the fen with dairy cattle sucklers and heifers up to the age of 18 months, but not beef cattle for fears of drop in quality. The cattle do not loose condition until this age, however in their second winter when they could loose condition, they are taken off the fen and put onto winter fodder. In the first two years of active management on the fen, 106 cattle at a 0.7 stocking density have been as lightly grazing. The grazing is taken over by Konic and Welsh Mountain ponies at other times of the year.

Grazing is important as it helps maintain a diverse structure of plant communities that  enables light to penetrate the ground layer. This also avoid a thick impenetrable thatch of vegetation of build-up and fully decompose on the surface. Some more sensitive areas of vegetation were strim-cut by a team of local contractors, who would normally be laid-off in the winter due to a shortage of work. This is an example of how a wetland ecosystem can provide a valuable service to the local farming community. 

 

The Boring Bit

Location: Cors Erddreiniog, Isle of Anglesey, Wales 

Grid Ref: SH469820

Date:  Thursday 10th October 2013
Weather: Dry but cloudy (80% cover)