Managing nature for carbon
Accelerating the rate of carbon sequestration in natural systems is one option for mitigating the impacts of climate change. This includes increasing the amount of carbon held in soils and vegetation, and deep geological reservoirs. Carbon capture at source and storage in geological reservoirs is a long term solution that is dependent on further technological innovations. Soil and vegetation capture can be done now because they only demand a change in how we use and manage our land.
Understanding carbon resilience, and how we can manage the land to retain carbon in vegetation, soil and seabed sediments is essential if we want to mitigate effects of climate change.
Land management: soils
Soils are the main terrestrial store of carbon in Scotland containing over 3000 megatonnes of carbon. This represents about 60 times more than there is in Scotland's trees and plants. Even though Scotland is only one third of the UK land mass, its soils contain ~50% of the total UK soil carbon store (~6000 megatonnes) equivalent to 186 years of Scotland's total carbon dioxide emissions at current rates.
Our peatlands which hold most of our carbon store (53%). The depth of peat can be as much as 12m, representing up to 9000 years accumulation, although the mean depth is more like 2m. The deeper the peat soil the more carbon it stores. Undisturbed, active peatlands accumulate about 0.25 tonnes of carbon per hectare per year which is broadly equivalent to around 10% of the amount of carbon accumulated over the duration of a forest crop.
Its not just about Peatlands - other soils are an often overlooked part of Scotland's nature and landscapes, which provide the basis to many habitats and are an important carbon sink that needs to be well managed.
Scotland's soils are already very rich in organic carbon and options to further improve carbon capture are more limited compared with the rest of the UK. Agricultural soils have the greatest potential for increased carbon sequestration. It has been estimated that agricultural soils could take up an additional 115 megatonnes of carbon, which is equivalent to 22 % of total carbon dioxide emissions from the energy sector.
A wide range of materials, including farm manures and slurries, sewage sludges, composts and other non-agricultural wastes are used in farmland, forestry, land restoration, landfill reclamation, landscaping and domestic gardens. Application of organic materials to land has the potential to increase the carbon stock of Scottish soils at a time when there is evidence that soils may be losing carbon at rates hitherto unforeseen. Over the next few years there is likely to be a significant increase in the production of composts from green waste and other organic materials that are diverted away from landfill in order to meet the UK's recycling targets. However, the availability of a suitable landbank, at both a national and local level, will be a key factor in deciding to what extent it is feasible and practical to increase recycling of non-agricultural materials in Scotland.
There is also growing interest in biochar (this is charcoal-like material created by pyrolysis of biomass) as a potential means to help tackle climate change by enhancing soil carbon sequestration and limiting carbon flux exchange. In others part of the world, where biochar is traditionally used it also has an added advantage in helping to improve soil fertility. This may be less relevant in already carbon rich Scottish soils like our peatlands and wetlands.
Land management: vegetation
There is an estimated 50 megatonnes of carbon locked in Scotland's vegetation, most of it being held in natural woodland and forest plantations. Woodland and forest covers over 1.3 million ha in Scotland (around 16% of Scotland).
Growing trees is one way to increase our natural carbon reservoir. The amount of carbon sequestrated by forest depends on the species of tree and the duration of the crop rotation. It can vary between 700 to 800 tonnes of carbon per hectare. Young forests grow rapidly and soak up carbon more quickly than mature forests. In mature forests the carbon balance may reach a steady state as carbon storage is matched by decomposition. Growing wood to use as a fuel is carbon neutral and provides a sustainable alternative to burning fossil fuels.
The Scottish Government aims to substantially increase the woodland cover up to 25% of Scotland. It will be important, however, to ensure this is done without releasing potential greenhouse gases from the soils in the process.
Marine management: 'blue' carbon
The global ocean plays a vital role in trapping and storing atmospheric carbon dioxide a greenhouse gas that would otherwise remain in the atmosphere and contribute to global warming. Scotland has around 470,000 square kilometres of seas in which more than 1,700 megatonnes of inorganic carbon, in the form of calcium carbonate, are stored as non-living material such as mollusc and crab shells, and the skeletons of microscopic plants (phytoplankton) coral, and maerl.
So-called 'blue' carbon is captured and stored across a range of seabed types such as kelp forests, saltmarsh, seagrass beds, cold-water coral reefs, flame shell and mussel beds and maerl that play a vital role in tackling climate change, much the same as onshore peatlands. But these habitats face challenges - maerl beds and coral reefs are subject to climate change and trawling, while seagrasses and saltmarsh can be affected by coastal erosion and various development activities. When damaged, these habitats cannot retain as much carbon and may become a source of greenhouse gases.
Many of these carbon storing habitats are on a list of features which could receive protection under a Nature Conservation Marine Protected Area (MPA).
All coastal plants and animals involved in carbon sequestration are potentially vulnerable to local impacts, but the effect of climate change is probably the biggest and least understood effect on the rate of capture and storage of carbon in Scottish seas. Find out more about Scotland's blue carbon stores by opening the Commissioned report in related links above.
Last updated on Tuesday 1st March 2016 at 14:22 PM. Click here to comment on this page