By Greta Dargie
The Congo Basin is the second largest drainage basin on the planet, draining 3.7 million squared kilometres. In the centre of the Congo Basin, shared between the Republic of Congo (ROC) and Democratic Republic of Congo (DRC), is a shallow depression, overlaid by swamp vegetation, known as the Cuvette Centrale. A few grey literature sources since the 1950’s mention that within the Cuvette Centrale it is possible to find peat, a wetland soil comprised of semi-decomposed plant material, which has a very high carbon (C) content. However, as these sources do not provide the locations of the peat deposits, the presence of peat beneath the swamp vegetation of the Cuvette Centrale was unconfirmed.
Myself and a team of researchers, from both the UK and Republic of Congo, therefore set about to establish whether peat was present within the Cuvette Centrale.
Given the size of the region, we used multiple satellite products to first identify areas thought likely to have environmental conditions suitable for peat development. Our search focused on the north of the ROC in the Likouala Department, where we carried out extensive field campaigns, covering an area of 40,000 km2 and visiting a total of eight field sites, all thought likely to harbour peat. At all eight sites peat was found and there was a strong association between vegetation type and peat presence, with a palm-dominated swamp and hardwood swamp found to be indicative of peat.
By combining our ground data with satellite data, we were able to use this vegetation-peat relationship to map peatlands across the Cuvette Centrale. Our results, which were recently published in Nature, show the peatlands of the Cuvette Centrale to be the largest tropical peatland complex on the planet, covering an estimated 145,500 km2 (95% CI: 131,900–156,400 km2). Using this area estimate and our data on peat depth and carbon density, we estimate that 30.6 Pg C (95% CI: 6.3–46.8 Pg C) are stored in the Cuvette Centrale peatlands-a quantity that is similar to the above-ground C stocks of the tropical forests of the entire Congo Basin. In a global context, our results increase the tropical peatland C stock estimate by 36%, to 104.7 Pg C. This finding places the DRC and the ROC as the second and third most important country in the tropics for both peatland extent and C stocks, behind Indonesia. Whilst Indonesia has the largest tropical peatland extent and C stock, these peatlands are under threat. Agriculture, forestry and palm oil plantations have caused the extensive degradation and destruction of South East Asian peatlands. Aside from the devastating impact on the biodiversity, this land use change has led to very large greenhouse gas emissions. Whilst the Cuvette Centrale peatlands are relatively intact, it is important that action is taken now to avoid a similar scenario to that seen in South East Asia.