Today’s guest blog has been written by Dr Paul Gaffney, former PhD student and hydrochemist at the Environmental Research Institute, on his work with RSPB centre for conservation science at Forsinard Flows.
Although peatlands cover just three percent of the Earth’s surface, they provide an important range of ecosystem services to society, include nature conservation, water regulation and carbon storage. Crucially peatlands store around one third of the world’s soil carbon in the peat.
Compared to most soils, peat is unusual because it forms on continuously wet ground. This means that decomposition of vegetation, which normally happens (like compost) in the presence of oxygen, has to happen underwater in the near-absence of oxygen and so it occurs a lot slower.
Through slow decomposition, dead vegetation forms peat, rich in carbon captured through photosynthesis from the atmosphere when the plants were alive. The amount of carbon stored in this way is greater than that lost from decomposition and so results in an overall net accumulation of carbon. 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 is more than eight thousand years old.
Sphagnum mosses are a vital part of the peatland ecosystem © Eleanor Bentall (rspb-images.com)
Why does peatland need restoration?
In recent times drainage to improve grazing and for forestry has been common practice. This has meant a loss of specialist vegetation, such as Sphagnum mosses, and lowering of the water table. In some cases, as decomposition increased, this has switched peatlands from net sequestration, to becoming carbon emitters. The good news is that these negative impacts have been recognised and has led to a global increase in peatland restoration.
While there are clear biodiversity and long-term climate benefits to restoring peatlands, there are still some uncertainties around carbon losses, particularly in the short term. Initially sites being restored may continue to emit carbon, only switching over time as they recover. There is also a clear need to understand whether restoration increases carbon concentrations in peatland water.
The Flow Country
80% of the UK’s peatlands are in Scotland and mostly in the form of blanket bog. 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. 20% of the peatlands here were drained and afforested with non-native conifers during the 1950s-1980s.
Over the last twenty years, restoration of drained afforested peatlands (or ‘Forest-to-bog’) 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.
Forest-to-bog restoration in action – the first stage is felling the trees and stripping the brash (branches and tops), which is harvested separately from the stems © Ainoa Pravia
In our new paper, published in the journal Science of the Total Environment, we measured the concentration of aquatic carbon from three catchments (one restoration catchment, one afforested control, one open bog control) over two years.
In the first year, the three catchments were compared before restoration. In the second year 12% of the restoration catchment underwent “forest-to-bog” restoration (conifers were harvested and the main forestry drains were blocked) whilst the two control catchments remained unchanged.
The author setting up a stream depth logger © Paul Gaffney
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, perhaps more related to rainfall and water table depth, which differed between years.
Automatic stream water sampler in action © Mark Hancock
Conifer brash decomposition may have contributed to increased summer aquatic carbon concentrations in the restoration catchment, as has been found previously by others. Although constrained by the length of the study, the results suggest that differences in rainfall between the study years played an important role in determining aquatic carbon export from the catchments.
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, restoring small areas, e.g., around 10% of a catchment, should help to minimise aquatic carbon loss following restoration.
This collaborative project is between the Environmental Research Institute, North Highland College, University of the Highlands and Islands and the RSPB Centre for Conservation Science.
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