Tale of the two peatlands! Cord Erddreiniog and Migneint

A return trip to Cors Erddreiniog, eastern Anglesey took us to look at the some of the important management processes in place. It also took us to the Migneint blanket bog, an area of peatland stretching over the counties of Gwynedd and Conwy in North West Wales.

Peatland in a Wetland context!

At the fundamental level you need three ingredients to have a wetland, water (or a hydrology at the soil surface or within the root zone), soil (in a hydric state) and vegetation (the presence of hydrophytes, adapted to wet conditions). These three ingredients are inter-related meaning water conditions must be such that will induce soil conditions to support wetland plants, i.e. you have all three, you have a wetland!  

At the next level the two prerequisites necessary for a peatland type wetland to occur are firstly, a positive water balance, meaning precipitation and the supply of other water sources is greater the evapotranspiration.  Secondly, primary production is greater than decomposition, meaning plants die faster than they can be decomposed. Essentially, peat is partially decomposed organic material originated from vegetation.

Now, let’s clear up some terminology related to the ecosystem development processes that lead to the formation peatlands. Peatlands can be split into bogs and fens, the key determining factor of this split is the water source. In the first instance, a peatland open to sources of water other than precipitation is classed as a fen or minerotrophic peatland. This is due to the mineral influences on the peatland from surrounding soils. They are usually flat and characterised by graminoid vegetation. In contrast, a bog can be described a peatland that receives water exclusively from precipitation and is termed an ombrotrophic peatland, they are usually raised above the landscape and support Sphagnum dominated vegetation.  

Sphagnum moss 

The Migneint (area: 2750 ha, altitude: 300-712 meters, terrain: waterlogged hill-slope) is a blanket bog, meaning the peatland has exceeded its’ original basin boundaries and spread from the site of peat initiation, to blanket the previously dry surrounding landscape. This process is called paludification and occurs only when rainfall is experienced throughout the year with no significant dry season. Blanket bogs begin life as a fen in a depression, becoming a raised bog, subsequently spreading out like a blanket covering and taking the shape of the landscape.

View of the Migneint from the road at Ysbyty Ifan. The brown stripes running vertical

down the slope of the right hand side a drainage ditches.

Cors Erddreiniog, however is a fen (ca.289 ha, altitude 5-10m, terrain: waterlogged and flat) receiving the majority of its’ water from a series of limestone springs. The fen began life as a post-glacial marl lake after which sedimentation build up kick started terrestrialisation from its’ bed outwards exceeding the basin and spreading via paludification. This development process is called flowthrough succession and is an intermediate between terrestrialisation and paludification.

Both of the peatlands described have suffered disastrous consequences from land drainage.  At Erddreiniog, peat cutting and fertiliser enrichment from run-off and leaching from the surrounding upland grazing pasture have added to the hydrological problems. The fen has suffered from drainage due to reclamation of land for agriculture (i.e. growing carrots). As a result, the water loss can exceed the water supply into the ecosystem leading to net water loss and increased oxygen availability in the soil.

The arterial drain at Cors Erddreiniog taking water out of the fen,

which eventually ends up in the Cefni reservoir.

The major implication of water loss is oxic conditions, under which microbes produce the enzyme phenol oxidase which breaks down phenolic compounds, when phenolic compounds are broken down, hydrolase enzymes kick in to break down non phenolic plant matter. The result, dissolved organic carbon (DOC) is leached in to the water course being easily oxidised and lost to the atmosphere as CO₂, one of the main GHG’s and contributors of global warming and the peat is washed away!  Under anoxic (waterlogged) conditions however, phenol oxidase is supressed due to the lack of oxygen and cannot break down phenolics. The resulting accumulation of phenolic compounds supress the activity of hydrolase enzymes that microbes produce to break down non-phenolic plant matter. The result, peat is formed and sequesters carbon!

One of other key implications on peatland drainage is biodiversity loss.  When a peatland is drained it cannot support the specially adapted wetland vegetation as the soil is aeriated and the obligate anaerobes die off.  If not for the intervention of a dam and wier system at Cors Erddreiniog, holding back the water in the arterial drain, the water and therefore the peatland would be entirely lost. On the flipside, water can be released to lower the water levels of the fen during storm surges to protect it from flooding.

The dam and weir structure at Cors Erddreiniog holding back water in the fen.

This footage is showing the wier in action at Cors Erddreiniog.

Another key implication of drainage at Erddreiniog is its detrimental effects of water quality. The DOC enriched brown fen water drains into the Afon Cefni which feeds the Cefni reservoir. DOC removal from drinking water is the most expensive process of the water purification process. The danger however is when chlorine is used in the water purification process and DOC is present, trihalomethanes a suspected carcinogen accumulate in low concentrations.

­­­­­On the Migneint, drainage due to grouse management has had devastating effects of the peatland. The implications of drainage are the same in that a drained peatland has the inability to sequester carbon and loses its unique biodiversity which has implications for both global warming and biodiversity.

A peat erosion complex on the migneint. 

It is unclear why the patches remain as they are and are not washed away.

Conservation efforts in order to restore the peatlands back to their former condition pre-drainage have been made on both, given the implications outlines, I think that is money well spent! At the Migneint, the National Trust have concentrated on blocking draining ditches in an experimental study that compares the effectiveness of three damming methods, one damming with peat, one damming with straw bales and one damming with a synthetic artificial dam construction. The results are having a positive effect for global warming as CO₂ emissions are decreasing as ditches are being blocked and converting it from a net source to a net sink of carbon. The formation of bog pools that can provide a habitat for freshwater macro-invertebrates and macrophytes and subsequently biodiversity at the higher trophic level.

Experimental damming site, measuring discharge using V notch wiers

At Cors Erddreiniog as described in my second blog pot, conservation efforts are taking place in the form of re-wetting the peat surface by reconnecting previously intercepted springs to the fen in order to create conditions for target vegetation using the WETMEC’s framework, grazing is also introduced at a stocking density of <1 livestock unit to control the vegetation.

Life above the peat!

The biodiversity difference between the two sites is striking upon first arrival to the Migneint bog, the second stop of the day! The Migneint flora is comprised of short vegetation barely reaching 40 cm height, mostly consisting of Sphagnum mosses at ground level as well as Ling heather (Calluna vulgaris), Cotton-grass (Eriophorum), Lichens (Cladonia), and Bladderwort (Utricularia) in the bog pools. 

   

Ling (Calluna vulgaris) at the Migneint blanket bog

Cotton-grass (Eriophorum) at the Migneint

A drinker moth caterpillar on the Migneint. The blanket bog has a specialised

biodiversity due to the low pH, low productivity and lack of tall vegetation for 

protection and shade. 

Bog pools forming where the slopE levels, are good for aquatic plants and invertebrates

Bladderwort (Utricularia) forming in the Bog pools. Bladderwort is carniverous
like a sub-aquatic venus fly trap.

  

At Erddreiniog, the vegetation can exceed head height and is made up of primarily graminoids such as Cladium, Carex, Juncus, Phragmites and Typha as well as mosses as well as flowering plants such as Fly Orchid and Narrow-leaved marsh orchid.

Cladium mariscus (Saw sedge) beds at Cors Erddreiniog

Close up of Cladium bed with Myrica gale (Bog myrtle) interspersed throughout

Phragmites australis bed (Common Reed)  a Graminoid species at Cors Erddreiniog

Both peatlands support plants adapted low nutrient levels, however they contrast in that Cors Erddreiniog has a higher nutrient availability as a result of the mineral influences from surrounding mineral soil. This is evident when you look at biomass differences and vegetation height. Primary productivity is lower at the Bog as nutrient availability and acidic conditions limiting growth. The pH of the Bog is low as the Spagnum releases phenolic compounds and organic acids as it decomposes, this gives itself a competitive advantage however, other species can compete in the acidic environment. At the Erddreiniog the pH is higher due to the input of minerals from the surrounding soil, especially calcium which swings the balance to a slightly basic circum-neutral to basic pH. Conductivity is also low (30-44 ) due to the lack of minerals, whereas the conductivity at Erddreiniog is higher in comparison (47-61).