Blog by Dr Paul Gaffney
In this article, we explain the background to peatland restoration and some of the key findings of this study. A shortened version of this blog article is available from the RSPB website: here
A new paper investigating the effects of restoration of drained afforested blanket bog in the Flow Country on aquatic carbon loss has recently been published, as part of a collaborative project between the Environmental Research Institute, North Highland College, University of the Highlands and Islands and the RSPB Centre for Conservation Science. These findings contribute to the evidence base informing management of afforested peatlands. The key finding of this short term (1 year) study, was that no significant effects on aquatic carbon export were found following restoration (by conifer harvesting and drain blocking) of 12% of the catchment area.
Peatlands cover approximately three percent of the Earth’s surface but provide an important range of ecosystem services to society, including nature conservation, water regulation and carbon storage (Bonn et al., 2016). Crucially, on a global scale, peatlands store approximately one third of the world’s soil carbon in the peat (Parish et al., 2008). Peatland vegetation sequesters atmospheric carbon dioxide through vegetation photosynthesis. Due to the waterlogged anoxic conditions, the inputs of carbon via photosynthesis are greater than the outputs from decomposition (through both gaseous and aquatic pathways) resulting in net carbon accumulation. Through slow decomposition, dead vegetation forms peat – which is rich in carbon, captured from the atmosphere when the plants were alive. Over time, as long as conditions remain cool and wet, peat continues to form, the peat deposit grows (at a rate of about 1 mm per year) and it is not unusual to find peatlands where the bottom layer (several metres below the surface) is more than eight thousand years old.
However, climate change, land management and industrial development are all threats to the long-term fate of the carbon stored in peatlands (Joosten and Clarke, 2002). In relatively recent times (compared to the age of a peatland) drainage to improve grazing and drainage for forestry has been common practice on peatlands. This has caused degradation (lowering of the water table, loss of specialist vegetation), followed by a loss of ecosystem services including in some cases a switch from carbon sequestration to carbon emission, as decomposition of aerated peat increased. The wider recognition of the negative impacts of degradation of peatland ecosystems and the costs associated with the loss of ecosystem services has led to a global increase in peatland restoration (Andersen et al., 2016; Bonn et al., 2016). Peatland restoration aims to halt degradation and put degraded peatlands back on a functional trajectory towards that of intact peatlands (Hancock et al., 2018) and is supported (financially and through policy) by many government and intergovernmental organisations.
The UK has more than 21 000 km2 of peatlands (with a minimum depth of 45cm), 80% of which are in Scotland and mostly in the form of blanket bog (i.e. rain fed, nutrient poor peatlands which cover entire landscapes like blankets) (Cannell et al.,1993). The Flow Country peatland of Caithness and Sutherland in Northern Scotland covers 400 km2, making it the largest remaining expanse of blanket bog in Europe, and a site of global significance. Here, 20% of the Flow Country peatlands were drained and afforested with non-native conifers during the 1950s-1980s (Sloan et al., 2018). In the last twenty years, restoration of drained afforested peatlands has been undertaken by many land-owners across the Flow Country and in other regions in the UK, after being pioneered by the RSPB on the Forsinard Flows National Nature Reserve.
While there are clear biodiversity and long-term climate benefits to restoring drained afforested peatlands (Morison et al., 2010; Wilson et al., 2014; Hancock et al., 2018; Vanguelova et al., 2018; Hambley et al., 2019; Hermans et al., 2019; Lees et al., 2019) there are still some uncertainties around net carbon losses (particularly in the short term), where restoration can represent a physical and biogeochemical disturbance (Gaffney et al., 2018; Hermans et al., 2018). Initially restoration sites may be net sources of gaseous carbon, recovering through time to become net carbon sinks as they move towards intact conditions (Hambley et al., 2019; Lees et al., 2019). Through the aquatic pathway, following restoration there is also the potential for increased aquatic carbon concentrations (Gaffney et al., 2018). Thus, there is a clear need to understand the effect of restoration on aquatic carbon loss or export.
In the present study, aquatic carbon export was measured from three catchments (one restoration catchment, one afforested control, one open bog control) in a before-after-control-impact design over two years. In the first year, the three catchments were compared prior to restoration, while in the second year, 12% of the restoration catchment underwent “forest-to-bog” restoration, where conifers were harvested and the main forestry drains were blocked; meanwhile, the two control catchments remained unchanged.
Water samples were collected during a range of flow conditions from the outlet stream in each catchment, and analysed for aquatic carbon concentrations. The sampling included high flow storm events, known to carry disproportionate amounts of carbon. In these streams, water depth was continuously logged, which was translated into continuous stream discharge estimates, by establishing a stream depth-discharge relationship. The combination of stream water carbon concentrations and the stream discharge (volume of water flowing out per second) allows calculation of the export or loss of aquatic carbon. We found that following restoration, there were no significant changes in aquatic carbon concentrations or export when comparing the pre- and post-restoration periods between catchments. There was around a 50% increase in summer aquatic carbon concentrations in both the restoration and open bog control catchments, thus not directly associated with restoration but perhaps more related to precipitation patterns and water table depth, which differed between years. Nonetheless, conifer brash decomposition may have contributed to increased summer aquatic carbon concentrations in the restoration catchment, as has previously been found by others in surface water post-restoration (Gaffney et al., 2018; Shah and Nisbet, 2019). Although constrained by the length of the study (i.e. a longer study may allow greater comparison of restoration and climatic / hydrological factors), the results suggest that differences in precipitation patterns between the study years played an important role in determining aquatic carbon export from the catchments (pre-restoration lower carbon export – deeper water tables, fewer rain days meaning summer droughts, but higher annual precipitation; post-restoration – higher export – shallower water tables, more rain days, but lower total annual precipitation). As “forest-to-bog” restoration was carried out on a small percentage of the catchment, effects of restoration may simply have been diluted by the undisturbed area. Therefore, in contexts similar to the study, restoring small areas, e.g., around 10% of a catchment, should help to minimise aquatic carbon loss following restoration.
The paper was published in Science of the Total Environment (https://doi.org/10.1016/j.scitotenv.2020.140594) and can be found here https://authors.elsevier.com/a/1bLroB8ccoIAi (50 days free access link).
REFERENCES:
Andersen, R., Farrell, C., Graf, M., Muller, F., Calvar, E., Frankard, P., Caporn, S., Anderson, P., 2016. An overview of the progress and challenges of peatland restoration in Western Europe. Restor. Ecol. 25, 271–282.
Bonn, A., Allott, T., Evans, M., Joosten, H., Stoneman, R., 2016. Peatland restoration and ecosystem services : science, policy, and practice. Cambridge Univeristy Press, Cambridge.
Gaffney, P.P.J., Hancock, M.H., Taggart, M.A., Andersen, R., 2018. Measuring restoration progress using pore- and surface-water chemistry across a chronosequence of formerly afforested blanket bogs. J. Environ. Manage. 219, 239–251.
Hambley, G., Andersen, R., Levy, P., Saunders, M., Cowie, N.R., Teh, Y.A., Hill, T.C., 2019. Net ecosystem exchange from two formerly afforested peatlands undergoing restoration in the Flow Country of northern Scotland 23, 1–14.
Hancock, M.H., Klein, D., Andersen, R., Cowie, N.R., 2018. Vegetation response to restoration management of a blanket bog damaged by drainage and afforestation. Appl. Veg. Sci. 1–11.
Hermans, R., Andersen, R., Artz, R., Cowie, N., Coyle, M., Gaffney, P., Hambley, G., Hancock, M., Hill, T., Khomik, M., Teh, Y.A., Subke, J., 2019. Climate benefits of forest – to – bog restoration on deep peat, ClimateXChange. Edinburgh.
Hermans, R., Zahn, N., Andersen, R., Teh, Y.A., Cowie, N., Subke, J.A., 2018. An incubation study of GHG flux responses to a changing water table linked to biochemical parameters across a peatland restoration chronosequence. Mires Peat 23, 1–18.
Joosten, H., Clarke, D., 2002. Wise use of mires and peatlands: background and principles including a framework for decision-making. International Peat Society International Mire Conservation Group, Saarijärvi, Finland.
Lees, K.J., Quaife, T., Artz, R.R.E., Khomik, M., Sottocornola, M., Kiely, G., Hambley, G., Hill, T., Saunders, M., Cowie, N.R., Ritson, J., Clark, J.M., 2019. A model of gross primary productivity based on satellite data suggests formerly afforested peatlands undergoing restoration regain full photosynthesis capacity after five to ten years. J. Environ. Manage. 246, 594–604.
Morison, J., Vanguelova, E., Broadmeadow, S., Perks, M., Yamulki, S., Randle, T., 2010. Understanding the GHG implications of forestry on peat soils in Scotland, Forest Research. Edinburgh.
Parish, F., Sirin, A., Charman, D., Joosten, H., Minayeva, T., Silvius, M., Stringer, L., 2008. Assessment on Peatland, Biodiversity and Climate Change, Global Environment Centre, Kuala Lumpur & Wetlands International, Wageningen.
Shah, N.., Nisbet, T.., 2019. The effects of forest clearance for peatland restoration on water quality. Sci. Total Environ. 693, 133617.
Sloan, T.J., Payne, R.J., Anderson, A.R., Bain, C., Chapman, S., Cowie, N., Gilbert, P., Lindsay, R., Mauquoy, D., Newton, A.J., Andersen, R., 2018. Peatland afforestation in the UK and consequences for carbon storage. Mires Peat 23, 1–17.
Vanguelova, E., Chapman, S., Perks, M., Yamulki, S., Randle, T., Ashwood, F., Morison, J., 2018. Afforestation and restocking on peaty soils – new evidence assessment, ClimateXChange. Edinburgh.
Wilson, J.D., Anderson, R., Bailey, S., Chetcuti, J., Cowie, N.R., Hancock, M.H., Quine, C.P., Russell, N., Stephen, L., Thompson, D.B.A., 2014. Modelling edge effects of mature forest plantations on peatland waders informs landscape-scale conservation. J. Appl. Ecol. 51, 204–213.
