How is Peat Mined from Peatlands?
The extraction of peat, no matter what its ultimate use may be, involves a basic series of procedures. Drainage is almost always the essential first step in the mining process to dry the peat and make it more manageable to extract, process and transport. Controlling the hydrology of the peatland (its water table) is necessary for its successful exploitation.
Drainage of a peatland can be accomplished in a few different ways using a few different methods. Direct drainage involves the digging of ditches around the wetland to remove water from the area. Reduction in "basal area" requires the removal of peat that leads to drying effect that snowballs to further remove moisture from the wetland. This peat removal may also help to lower the resistance to the downward draining of water. Another method involves dehydration through lowering of the groundwater table, adjacent waterways, or both. Additionally, either through man-made placement or natural invasion, plant species start to grow in peatlands, increasing their relative rates of evapotranspiration, drying them out. Evapotranspiration is the loss of water from plants, either by evaporation or plant transpiration. Transpiration is the loss of water through plant cells.
(For a more detailed explanation of evapotranspiration, please visit this external page.)
After drainage of the area is achieved, the peat then must then be removed. There are three major methods that can be used with the actual peat removal; these include cutting the peat in peat blocks with machine or by hand, peat milling, and “sausage cutting”.
Peat cutting is the most customary form of peat removal as it can be done by hand or by machine. When done my hand, it usually involves the removal of the peat to a depth of 1 -2m, while working into the wetland. As explained above, removing peat caused a snowballing effect of drying that provides enough drainage necessary for extraction. The cut blocks are then placed in neat piles to dry out for a number of weeks before they may be transported. This is generally regarded as the least damaging way to extract peat. This is because it is usually done on a small scale as well as the fact that surface layers of peat are not preferred for fuel burning and are therefore placed back on the cutover area. This provides a surface for vegetation re-growth important to peatland renewal. It has been suggested that recovery can happen around 3 years after cutover if this surface turf is replaced again properly. If this is not done, peat erosion and invasive vegetation may negatively impact the area. This hand cutting method is still present in some areas, but it is largely being substituted for extraction by tractor-towed extrusion machines, or “sausage cutting”.
"Sausage cutting" involves the removal of peat beneath the surface that is then brought up through slits. This produces “sausages” of peat that can be cut to form convenient logs for fire places. This process could be arguably less detrimental to peatlands as the surface vegetation is mostly left intact, however more peatland area must be mined to produce the same amount of peat as block-cutting, possibly off-setting any benefits.
Machine-based block-cutting extraction is much the same as when done by hand in that the blocks are cut, stacked and finally transported when they are light enough from drying. The difference is the scale between machines and manual work, machines covering much larger areas. Machines are also used to turn over the blocks to facilitate a faster rate of drying. This method leads to leaving a pattern of hollow areas in the peatland referred to as “baulks”, then the area is abandoned.
Most recently, peat milling has become the main method in which peat is mined from an area. For this process, the surface of the peatland is drained and leveled by digging drains 15 m apart. The drain depth is gradually increased, meaning this type of preparation takes approximately 3 years to complete. It is done to prevent peat collapse that can occur with moist peat. The drainage process is sometimes also helped by cambering the peat, the arched surface lets water run off more quickly. When draining and leveling of the area is complete, the “peat field” can now support the heavy extraction machines. The peat is extracted using a vacuum harvester and then moved to an area off-site. As the peat depth decreases with every harvest, more and more drainage is needed, requiring drains to be dug deeper for the next harvest season.
Commercial peat extraction’s ultimate outcome is the large area of exposed peatland it leaves behind. Usually at least a depth of 0.5 m is removed, and sometimes more depending on the peat accumulation in an area. After such removal, the peatland is decimated, providing no habitat for wildlife and can no longer be of any recreational use to society for hunting or enjoyment of nature. Historically, these barren remnants were only seen suitable for agriculture or forestry. At present, this is slowly changing and efforts to restore peatlands after extraction activities are being made, a process that can be explored on this page of the website.
In addition to the demolition of the natural peatland ecosystem, other environmental issues can be caused by extraction. This includes the release of particulate carbon, dissolved organic carbon and heavy metals that run-off and subsequently end up in waterways. There is also the emission of carbon dioxide through combustion and decomposition peat during and after production. These potential environment effects can be explored on this page of the website.
ENVR 4000 Sustainable Water Management 2012