Effects of Peat Extraction on Peatlands
Large scale industrial production which removes peat by the milling process produces a cutaway bog. The process involves removal of the original surface peat forming vegetation. A series of drains are installed to form a grid-like system over the entire peatland. The peat fields intervening between the drains are 15m wide and shaped in such a way that the centre of the field is 23cm higher that the two sides at the drain edges. The drainage process of the peatland may take place by gravity or by means of pumping depending on the location of the site. The peat is removed over many years. A site is only taken out of production when there is no economic supply of peat remaining. The nature of the peat remaining in a cutaway bog is not uniform, its thickness may vary over the site and in some intances the underlying substrate may be visible.
The effects of industrial peat extraction are drainage, peat removal, peat compaction, expansion of non-peat forming vegetation types, peat instability, changed soil chemistry conditions and the exposure of the underlying substrates.
Rehabilitation of Cutaway Peatlands in the Midlands of Ireland
In the Midlands of Ireland, the after use of cutaway peatlands has involved rehabilitation of cutaways into wetlands, lakes, grassland, woodland and amenity areas. The showcase project for this work is the Lough Boora Parklands in Co. Offaly. This site is owned and managed by Bord na Móna. Part of the work has involved recreating old farmland pastures to help conserve the Grey Partridge. Consideration is also being given to managing naturally recolonising areas of cutaway for endangered farmland birds such as Lapwing. The work of lake creation on industrial cutaway bogs involves, blocking drains and limited re-profiling of the substrate to create flat areas suitable for flooding and islands in the lakes.
Three approaches have been trialed with regard to recreating wetlands on former industrial cutaway bogs. These depend on the volume of peat remaining on the site.
Approach 1: Total Peat Removal leaving a lake basin 3-4m deep with a marl or calcareous soil base. A piped inflow of water is used to flood the area. Soil cores containing wetland plants are introduced. The cost in 2008 for this approach is Euro 20,000 to 25.000 per hectare created. For example Loch Clochan, Loch an Dochas and Finnamore Loughs in Lough Boora Parklands. These lakes are eutrophic with pH 8.
Approach 2: Partial Peat Removal leaving peat islands and a basin 1-2m deep. Banks are re-inforced with peat. Wetland plant seeds were sewn along the edges and allowed to colonise naturally. This example is spring fed but also has a pipe inflow. The cost in 2008 for this approach is Euro 500 per hectare created. For example Turraun in Lough Boora Parklands and Blackwater in Co. Offaly. This lake is mesotrphic with pH 7.45.
Approach 3: Complete peat substrate in a basin of varying depth. The outflow is blocked and the area left to naturally re-flood and re-vegetate. The cost in 2008 for this approach is Euro 200 per hectare created. For example Clongawney and the Derries Loughs in Lough Boora Parklands. These lakes are mesotrophic with pH 6.74.
World Wide Establishment of Sphagnum Moss on an Industrial Cutaway Bog – the Canadian Approach
The Canadian peatland restoration approach is based on active reintroduction of peat bog plant species and hydrological management in order to raise and stabilise the water level. It consists of surface preparation, plant collection, plant spreading, straw spreading, fertilization and blocking drainage. The starting point for the restoration process is a relatively deep acidic peat substrate from which only horticultural grade peat has been removed.
- The surface dry crust of hard peat must be broken up so that plants introduced are in contact with the peat substrate. Harrowing machinery is used. Between 5 and 10cm of the surface may need to be milled depending on local conditions. In addition excessive loose peat should be removed.
- Dome shaped harvesting fields need to be reprofiled, i.e flattened. Ditches need to be filled in or blocked.
- Sphagnum is harvested from a donor site. The top 10cm are removed using a rotovator to first break up plant fragments and facilitate collection. This material is then spread using a back mounted manure spreader. The recommended harvest area to spread area ratio is 1:10 harvest:spread.
- Straw mulch needs to be spread over newly innoculated Sphagnum moss on the field surface using a blower. A minimum quantity to use is 3000kg per hectare. This reparesents 25 to 30 four foot bales per hectare (10 to 12 per acre). A sideward straw spreader may be used to apply the straw. The advantage of using this machne is that the machinery does not have to pass over plant fragments during straw application.
- Fertilization is carried out once all of the previous steps are complete. A weak dose of granulated rock phosphate fertiliser is used. Use of other types of phosphorus containing fertilisers is not recommended as the concentration phosphorus that they contain makes it difficult to get an even spread due to such a low application rate. Also, high doses of phosphorus promotes invasive species such as birch. Nitrogen fertilisers are not required as disturbed peatlands already contain enough nitrogen to support their native flora. Rock phosphate releases just enough phosphorus over a long enough period of time to help promote the growth of species such as Polytrichum moss. Polytrichum mosses act as nurse plants that in turn promote the growth of Sphagnum mosses. A dose of 150kg of rock phosphate per hectare is recommended. Care should be taken however when any phosphorus containing fertilizer is used near to a watercoarse so as to avoid contamination.
- Drain blocking is the final step in the restoration work. For further information see our page on Restoration of Drained Peatlands.
For a more detailed description of the methods described above download the Peatland Restoration Guide: Second Edition by Francois Quinty and Line Rochefort.
Small Scale Sphagnum Growth Restoration Projects
The same principals are used for smaller scale Sphagnum growth projects. Depending on the size of the area to be restored, plant material can be collected and spread by hand, as can straw and fertilizer.
Text, Photographs and Images © Irish Peatland Conservation Council, Bog of Allen Nature Centre, Lullymore, Rathangan, Co. Kildare. Email: bogs@ipcc.ie; Tel: +353-45-860133.