As has been previously discussed in Robert’s blog, fertile soil is an incredibly important resource that is fast running out in many regions of the world. It is true that soil’s importance for agriculture (and sustainable development) cannot be understated, but I wish to focus on another aspect of soil in this week’s blog– its ability to store carbon.
One soil type in particular, peat, is an incredibly important form of carbon storage. Despite only covering 3% of the Earth’s land surface it contains a third of the carbon stored in soils, formed by the build-up of partially decomposed organic carbon, trapped in waterlogged and anoxic conditions. For this reason the preservation of peatland is of the upmost importance, and should be considered in sustainable development efforts in order to prevent the release of vast amounts of carbon into the atmosphere.
- Figure 1- Distribution of mires around the world. Source: International Peat Society, Available www.peatsociety.fi
When you picture peat it is typically in a cool and damp climate, such as in the highlands of Scotland or expanses of tundra within the Arctic Circle. This is because the cooler climates further impede the decomposition of organic matter and facilitate the formation of peaty soils. Recently, however, it has been discovered that peat forms in other regions too, and in quantities far vaster than had ever been considered before. These tropical peat deposits form in the swamps commonly found in the river basins of warm and humid regions. Although warm and wet conditions typically aid the processes of rot and decay, the often stagnant water of swamps produces anoxic environments not dissimilar to those in the extensive peatlands found at higher latitudes. Conditions are exacerbated by poor drainage, high rainfall and overbank flooding by rivers, meaning that the land never truly gets the opportunity to dry out and peatlands are able to form, albeit in much smaller expanses than those in the North.
Despite the smaller size of tropical peat deposits they are disproportionately more significant to sustainable development, as they tend to be focussed in regions where development is occurring rapidly – central Africa, South East Asia and South America. Building on and draining these fragile ecosystems could result in mass release of carbon dioxide.
An example of a tropical peat deposit is the Cuvette Centrale depression in the Central Congo basin, where the peat is relatively shallow (with a median depth of 2m), but has a large aerial extent, making it the greatest ranging peatland in the tropics. Other extensive peat deposits can be found in the amazon rainforest and in tropical Asia (for example the island of Borneo) but land use changes in recent years have drastically reduced the amount of peatland in SE Asia, as much has been drained for agricultural use. It is predicted that SE Asian peatland will be lost completely by 2030, but thankfully the peatlands in other areas of the world are in a significantly more pristine condition, relatively unaffected by humans due to their relative inaccessibility.
Drainage of land for agricultural use is not the only threat to tropical peatlands. Climate change is acting to reduce the annual precipitation in many tropical regions, meaning carbon trapped in peat is oxidised more readily and able to decompose. Even though tropical peatlands are only a fraction of the size of their northern, cooler cousins, they still represent huge carbon stores that, if destroyed, could accelerate the release of carbon into the atmosphere and accelerate global warming further, entering into a feedback loop which will release tonnes of carbon into the atmosphere that has lain trapped underground for millennia. Carbon stocks of peat in the Cuvette Centrale alone are potentially equal to 20 years of current fossil fuel emissions from the USA, demonstrating the importance of protecting this seemingly insignificant soil type.
- Figure 3 – SE Asian rainforest. It is in rainforests such as this that peatlands are quickly being drained for agricultural use. Source: https://imaggeo.egu.eu/view/4268/
A further concern is that swamplands are a refuge for many of the world’s remaining megafaunal populations, including lowland gorillas and forest elephants. It is clear that if Africa and South American peatlands are to avoid the fate of the SE Asian counterparts, they must become a conservation research priority. Doing this would undoubtedly help to combat the rise of CO2 levels and simultaneously work towards the UN Sustainable Development Goal 13 – climate action.
