World Soil Day: why we need to protect our peatlands from erosion

"Every year, we lose some of our precious agricultural soil to erosion, and, similarly, out of our 1.9 million hectares of peatland, about 270,000 hectares show evidence of peat erosion"

‘Erosion’ is partly a natural process where soil particles are transported by our rivers and streams to the sea. ‘Accelerated erosion’ however, is caused by inappropriate land use or land management and this is a global issue that affects our ability to manage soils sustainably. The Food and Agriculture Organisation (FAO) of the United Nations has estimated that a third of the world’s soils are already degraded. While much of this degradation is found in low-income countries, Scotland is not immune to the adverse effects of soil erosion.

Every year, we lose some of our precious agricultural soil to erosion, and, similarly, out of our 1.9 million hectares of peatland, about 270,000 hectares show evidence of peat erosion. Having nearly 15% of our peatlands eroding is very bad news for our efforts to respond to the global climate emergency. The Scottish Government has put into law the toughest targets to reduce greenhouse gas emissions by 75% by 2030, and to net zero emissions by 2045. With nearly a quarter of our land area covered by peatlands, restoration of 50,000 ha of degraded peatland areas by 2020 is one of the targets the current Climate Change Plan is hoping to achieve.

Peat erosion can contribute to a physical loss of peat of up to 4 cm per year in some locations. This used to be measured with pins that were anchored into the ground and measured again at regular intervals, but we don’t really know whether this peat actually disappears off the hill and into our watercourses, or whether it is simply redistributed further down a peat erosion gully. Our current estimates from monitoring greenhouse gas losses and water quality sampling are that just under 5 tonnes of carbon dioxide equivalents per hectare are disappearing completely from eroding peatlands each year and while some of this may be locked up in ocean sediments, eroded peat is unable to gain carbon compared with an intact, healthy bog. The brown water you frequently see in Scottish rivers is often due to dissolved peat and peat particles from erosion further uphill. Consequently, the water industry spends significant amounts of money each year to make our drinking water clean and clear.

Erosion in peatlands can take the form of minor ‘peat haggs’ around the edges, or, as in the image, large ‘peat gullies’ deeper than a person and wide enough to hide a car or even small plane can form. In some areas of Scotland, there will be hundreds of such peat gullies per hectare. Some forms of erosion are not even visible and cause so-called ‘peat pipes’ – tunnels below the ground through which water flows and which become larger as time progresses and may eventually collapse to form a new gully.

All our soils are under threat from a changing climate and peatlands are no exception. Extreme rainfall events such as that of 2016 (Storm Frank) are predicted to become more common (a recent report from the Met Office Hadley Centre suggested that there is a 34% chance of somewhere in the UK breaking a rainfall record each winter). These rainfall events can cause widespread erosion on unprotected or already damaged soils leading to increased flood risk, loss of soil nutrients and carbon, and pollution of our rivers.

A large programme of restoration is now ongoing to restore Scotland’s peatland habitat and to reduce carbon emissions and soil erosion losses. Eroded peatlands are extremely challenging to restore as they are more frequently found in our uplands and are more difficult to access. Restoration management aims to reprofile erosion gullies and cover bare areas with turfs or sphagnum-rich mulch. This is no mean feat when such sites are covered with snow for a substantial part of the year, experience high rainfall and wind speeds in the autumn and spring, and plant growth rates are so slow.

Research at the James Hutton Institute, in collaboration with Peatland Action (Scottish Natural Heritage) is focusing on measuring how much carbon is lost from eroded peatland before restoration efforts and then how effective restoration management is. We monitor greenhouse gas emissions on eroded peatland using a specialised weather station, which measures rainfall, windspeed, temperature and the amount of carbon dioxide released from the eroded area both before and after restoration management.

An additional project has also started to monitor how much carbon is lost through water flowing through erosion gullies and transporting peat downslope. By doing this we will be able to show how much carbon and greenhouse gas emissions we save with effective restoration and help Scotland achieve its net-zero targets.

Dr Rebekka Artz is a soil scientist within the Ecological Sciences group at the James Hutton Institute and wrote this article with Dr Allan Lilly to highlight World Soil Day, held annually on 5 December to focus attention on the importance of healthy soil and sustainable management of soil resources.