Peat plays a significant role as a water/carbon store and as a habitat. The island of Ireland has one of the highest concentrations of peatbog of any country worldwide, with 20% wetland coverage.
In fact, approximately 68% of the island of Ireland’s drinking water comes from peatland, whilst up to 75% of its soil carbon is in the form of peat.
A key focus for the Source to Tap project is investigating techniques for restoring peatland, which could be used to benefit drinking water quality. Water from healthy, intact peat bogs requires little treatment, as it is well filtered by the complex soil system. But when the bog is damaged, more carbon seeps into the water, colouring it and requiring costly treatment processes.
There is also evidence that greater quantities of sediment in our rivers and lakes can prevent fish from spawning.
Source to Tap has piloted peatland restoration techniques from forest back to peatbog. Different peat restoration methods have been trialled on the test site at Tullychurry, owned by Forest Service (DAERA).
The first step was to cut down the plantation forest that covered the land. The forest had been planted in a ridge and furrow pattern, creating pathways for water to escape, and so this needed to be addressed and water levels raised back up to prevent water from escaping from the site.
Two methods were trialled: cell bunding and drain blocking.
Sphagnum mosses play a vital role in the creation of peat bogs: by storing water in their spongy forms, they prevent the decay of dead plant material and eventually form peat. Therefore, getting the conditions correct to encourage its recolonisation is an important part of the restoration process. After the initial work raising the water table, some of the trial land was sprayed with a mix of sphagnum mosses to see whether this speeded up the process.
Deep trench or cell bunding is the construction of watertight cells made from low peat walls, constructed at a 90-degree angle to the slope with a bund roughly every 30 cm fall in height.
‘Finger bunds’ are then constructed at intervals in line with the slope, joining the parallel bunds to prevent lateral erosion and wave action. Creating these watertight cells allows the water table to rise, encouraging the growth of sphagnum moss.
Drain blocking is a popular method of peatland restoration. Peat dams were used to block drains and brash mats at 12 m intervals or every 30 cm drop in ground level. Dams were constructed using saturated peat from a borrow pit adjacent to the dam location.
The control area was designed to mimic existing forestry best practice when leaving a site to restore. In this area, drains were blocked with peat dams only where they exited the area.
Each of the three restoration areas was monitored using shallow groundwater dipwells. These were sunk around 1.5-2 m into the ground and used to monitor water table recovery post-restoration and collect samples which were analysed for colour and True colour. A fourth area of intact blanket bog and an area of standing trees were also monitored for comparison with the three treatment areas.
Results will be made available in a technical report in 2022 at the end of the pilot.