For Peat’s Sake!
Peatlands: the not-so-secret solution to our climate crisis
These drastically undervalued “Cinderella” habitats cover approximately 3% of the earth’s land area yet store almost 33% of the entire global soil Carbon pool and around 3-3.5 times that of the tropical rainforests (1,2). As an active carbon-accumulating, flood-alleviating, biodiversity haven – why are these instrumental carbon stores not being recognised for their potential in the battle against rising atmospheric levels of carbon dioxide?
It all starts with Sphagnum. Sphagnum mosses are small unassuming bryophytes that probably don’t strike you as the answer to global warming. They may be small but their unique and impressive physiognomy enables them to not only cope with, but seemingly control, the environment in which they thrive. In a constant cycle of growth, Sphagna develop from the apices of the plant and leave dead organic material at the base in a waterlogged state. In a constant cycle, the addition of dead organic matter far exceeds the loss through decay which results in layers of organic matter and water forming to produce peat.
The very nature of peatland carbon dynamics means that vast amounts of carbon can then be naturally, and continuously, sequestered. The UK’s peatlands store an impressive 4.5 million tonnes of carbon (3). These stores can outlast millennia providing, simply, that the habitat remains wet (4). In terms of flood risk alleviation, intact peatlands also act as large, self-regulating sponges that absorb rainfall and steady the flow of water into lower-lying ground.
So, if peatlands are as useful as they appear to be why aren’t they at the forefront of global climate change mitigation and adaptation solutions?
Unfortunately, Peatlands have been drained and cut extensively over past centuries. In the UK, commercial peat extraction removes peat at a rate far exceeding that of deposition. This is then utilised as a horticultural growing medium (despite equally effective and readily available peat-free alternatives). Globally, most bogs are now drained, cultivated or surrounded by urban expansion. As a result of this misuse, annual emissions from degraded peatlands constitute around 2-3 gigatonnes of CO2 per year (5). These incredible carbon storage systems are rapidly being converted into large-scale, dangerous carbon sources.
Anthropogenic alterations also have far-reaching catastrophic effects for the entire ecosystem. A change in the water table of even a few centimetres can destroy the delicate balance of wetland flora that often has particular requirements for water depth and its seasonal fluctuations. Man-made drains directly exacerbate the effects of rainfall which results in rapid run-off into ditches instead of slow percolation through the soil. These water surges have catastrophic effects on both the bankside plants and burrowing animal inhabitants (6). As sphagnum also compacts with drainage this further reduces permeability and increases the overall flood risk. Furthermore, peat oxidation and deflation results in an increased risk of ground subsidence (7).
Large-scale restoration appears to be the only current option for ‘fixing’ this man-made problem. Restoration ecology aims to regenerate a Carbon accumulating, self-sustaining ecosystem. Various methods have been developed but it still remains both difficult and expensive to restore near-natural conditions. Efforts generally focus on raising the water table to above, or close to, the soil surface in order to promote the re-establishment of wet minerotrophic vegetation and Sphagna.
Gammelmose in NE Denmark, one of the very first peatland restoration sites to be protected from human usage in 1844, has shown that autogenic recovery can be a successful method of ‘passive restoration’. (8) However, relying on spontaneous re-vegetation may be a risky strategy for large industrially exploited systems as sphagnum re-immigration can be extremely slow. Restoration could take more than a century in cutover peatlands left to revegetate spontaneously (9). In comparison, active peatland restoration through deliberate species reintroductions, such as the dispersal of sphagnum diaspores, could reduce the time taken for vegetative regeneration by around 70 years (9). Tuittila et al. (2000) also found that Sphagnum reintroduction increased Carbon binding and therefore directly improved on-site carbon sequestration (10).
Unfortunately, complete restoration is often impossible due to non-reversible physical changes in the upper soil layer. Increased oxygen saturation, as a consequence of drainage, increases the degree of peat decomposition which decreases hydraulic conductivity and increases the mobility of nutrients. Active rewetting processes then result in the production of shallow eutrophic lakes. However, both Zak et al. (2010) and Zak and Gelbrecht (2007) have demonstrated that the removal of this highly decomposed layer prior to flooding decreases these effects (1,11,12).
The main limitation for peatland restoration is a lack of long term data in this area of ecology. This often results in projects utilising trial and error methodology. As P. Anderson (2014) stated, in terms of peatland restoration efforts, “not everything can be, or is, researched” (13). New techniques have to be trialled but in such extensive projects there is often no real scope for large-scale experimentation due to the high costs involved.
Time-scales are also frequently unrealistic for projects involving these slow growing habitats. In the deepest parts of the Gammelmose peatland 1m of peat accumulated over 145 years and in other areas of this site little change was observed at all (8). Ten years after restoration measures were applied to a cutover part of the Boisdes-Bel Bog (Québec, Canada) a near complete 15cm thick Sphagnum moss layer was found. However, low overall moisture levels indicate further growth is needed (14).
In terms of effective management, the situation does appear to be slowly improving with peatlands starting to get the recognition they deserve. The UK government has stated its ambition for the horticultural sector to end peat use by 2030. The Environmental Stewardship agreements of 2015 will directly benefit large areas of both the Peak District and South Pennines peatlands. A recent online gov.uk petition has so far received over 27,000 signatures demanding more be done by the government to manage and alleviate flood risks. In their response to this, the government has highlighted peatland restoration projects as part of Defra’s upcoming 25-year environmental plan to “work with the natural systems that underpin the health of our environment” and reduce overall flood risk in the UK. As well as the publication of this plan by the end of the year, the announcement of a £2.3bn investment in flood protection by 2021 hopefully means further progress is to come.
However, successful long-term peatland regeneration still requires the development of effective propagation techniques and monitoring methodologies. These will need to be tested and proven in large-scale trials before being formalised for widespread use. These habitats lack long-term investment and deserve the opportunity to demonstrate both their benefits and their potential. Peatlands may appear unexciting; the ‘Cinderella’ of the ecosystems, but these under-funded, under-valued sites should definitely not be underestimated.
By Megan Scott, 4th Year BSc Biology
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Kollmann, J.C. and Rasmussen, K.K., 2012. Succession of a degraded bog in NE Denmark over 164 years–monitoring one of the earliest restoration experiments. Tuexenia, 32, pp.67-85.
Pouliot, R., Rochefort, L. and Karofeld, E., 2011. Initiation of microtopography in revegetated cutover peatlands. Applied Vegetation Science, 14(2), pp.158-171.
Tuittila, E.S., 2000. vegetation and carbon dynamics in a cut-away peatland.Canadian Journal of Botany, 78, pp.47-58.
Zak, D., Wagner, C., Payer, B., Augustin, J. and Gelbrecht, J., 2010. Phosphorus mobilization in rewetted fens: the effect of altered peat properties and implications for their restoration. Ecological Applications,20(5), pp.1336-1349.
Zak, D. and Gelbrecht, J., 2007. The mobilisation of phosphorus, organic carbon and ammonium in the initial stage of fen rewetting (a case study from NE Germany). Biogeochemistry, 85(2), pp.141-151.
Anderson, P., 2014. PRACTITIONER’S PERSPECTIVE: Bridging the gap between applied ecological science and practical implementation in peatland restoration. Journal of Applied Ecology, 51(5), pp.1148-1152.
McCarter, C.P. and Price, J.S., 2013. The hydrology of the Bois-des-Bel bog peatland restoration: 10 years post-restoration. Ecological Engineering, 55, pp.73-81.