Mapping the total organic carbon in the soils of the Congo

A map of the main landscape units of Congo containing 31 cartographic units was established using vegetation and parent rock types, particle-size distribution and hydromorphy in soils. The average carbon stock in each unit was calculated to a depth of 2 m. The hydromorphy and the particle-size distribution of soils seemed to be the main factors influencing the capacity of soils to store carbon. The average carbon content of Congo soils is 160.5 t/ha for a depth of 0–2 m. The total stock of organic carbon in the mapped area (302,000 km2) is 0.8 Gt at 0–10 cm, 3.3 Gt at 0–100 cm, and 3.9 Gt at 0–200 cm. The stock between 1- and 2-m depth is stable carbon. As its content is relatively constant with depth, the total amount of stable carbon can be roughly estimated at about 1.2 Gt. It could be a sink for carbon dioxide.