Degraded peatlands can contribute to high sediment levels in streams and rivers through erosion leading to increased levels of dissolved organic carbon (DOC) and colour in watercourses. In catchments such as the Erne and Derg which are abstracted for drinking water, this can lead to challenges during drinking water treatment as well as potentially impacting upon fish spawning grounds.
The Source to Tap peat pilot planned to restore an area of formerly afforested peat to active blanket bog. A 32.9ha site, in Tullychurry Forest, next to the internationally designated conservation site of Pettigoe Plateau, was planted by Forest Service NI in the 1960s. The peat was originally prepared for planting using double moldboard ploughing. This leaves a characteristic ridge and furrow pattern which must be addressed for effective restoration to ensure that the water table recovers sufficiently to support sphagnum recovery and re-colonisation.
The pilot aimed to compare the effectiveness of a restoration technique called cell bunding on the recovery of water table levels, with the more traditional method of drain blocking using peat dams.
Following harvesting, the site was split into three treatment areas.
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. By creating these watertight cells it allows the water table to rise and allow the growth of sphagnum moss.
Drain blocking is a popular method of peatland restoration. Peat dams were used to block each drain 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 and covered with vegetation and brash to prevent wind and rain erosion.
The control area was used to compare methods of current forestry best practice, observed on another restoration site, with other restoration methods. In this area, drains were blocked with peat dams only where they exited the area.
Each of the three restoration areas were monitored using piezometers. These are shallow groundwater wells which are sunk around 1.5-2 m into the ground and were used to monitor water table recovery post restoration. A fourth area, of intact blanket bog was also monitored as a comparison.
Results will be made available in a technical report in 2021 at the end of the pilot.