Spent bogs could provide important new conservation areas for all kinds of wildlife, writes Claire O'Connell.
What do you do with a spent bog? As more and more of Ireland's peatlands pass their usefulness for providing fuel, one option is to create artificial lakes in used boglands to conserve wildlife. But getting the conditions right is a balancing act, and a researcher at NUI Galway has been weighing up the best strategies for making conservation-friendly lakes in cutaway peatlands.
Harvested peatlands can be designated for non-commercial uses like tourism, fishing and conservation, explains Dr Tara Higgins, who completed her PhD at NUI Galway's department of microbiology. And given Ireland's extensive boggy coverage, the potential for creating new habitats is huge. By 2030, an estimated 80,000 hectares of milled peatland will be redundant here and around half of this area will be rehabilitated as lakes and surrounding wilderness.
The basis of creating a cutaway lake is to block up man-made drainage systems in a bog and let the site flood through a combination of groundwater seepage and rainfall. In some cases water may also be piped in from a nearby stream.
But Dr Higgins has found that the way in which a lake site is prepared, and particularly the sediment that lies at its base, can affect the new lake's water chemistry and the type of wildlife it will support.
As part of her project, which was funded by Bord na Móna, she monitored four experimental cutaway lakes in raised bogs in Co Offaly that had been created using different strategies. "It was the first examination of the water chemistry and the nutrient status, a baseline study of the artificial lakes," says Dr Higgins, who worked with Prof Emer Colleran. "The idea was to look at the water quality to maximise the conservation potential of the lakes."
She regularly collected six-litre samples from the different lakes and measured a range of attributes such as acidity, colour, nutrient levels and plankton content. "Plankton were good indicators of water quality," she explains. "The species types reflected the quality, such as hardness and silica, and abundance correlated with the nutrient status."
The most expensive of the lake-building schemes in her study was to scoop out peat sediment from the bottom of the lake site, boost irrigation with stream water and introduce plants and animals to speed up colonisation. The resulting lake type is deep and suitable for angling, but at €25,000 per hectare it's expensive.
At the other extreme, a lake can be created for a mere €200 per hectare by simply blocking the drainage channels and letting groundwater seep in. This lake has large amounts of peat at its base, making the water highly acidic, says Dr Higgins. "The pH of the acidic lake was 4.5, which is the same as orange juice - it's probably one of the most naturally acidic environments there is," she explains. "So there's going to be lower biodiversity because a lower number of species can tolerate that harsh environment. And the bare lake is not really attractive, it's a spooky environment."
Dr Higgins feels the most cost-effective and useful approach for conservation is the middle ground, where the bulk of peat is removed from the lake site's base, but some peat remains in mounds, creating a variety of local environments in the lake. The site is also seeded with vegetation. In total it costs around €500 per hectare. "The middle strategy is a balance," she says.
Dr Higgins also found that runoff from surrounding land could push up levels of nitrates or phosphates in the lake water and she recommends establishing a "buffer zone" of vegetation at the lake edges to help protect the vulnerable new ecosystems.
A lake's age is also an important factor. "You need to let things stabilise, so there's a need for future monitoring to get a bigger picture," she says, adding that another student, Heather Lally, is continuing the work.