Recent changes in the global carbon balance of tropical organic soils

Tropical organic soils, which store at least 90 x 10/sup 9/ gigatons (Gt) of organic carbon in upper layers, form a distinct pool in the terrestrial biosphere. Although ordinarily functioning as carbon sinks through the continuing storage of unoxidized plant residues, the pool as a whole now appears to be undergoing a transition with respect to carbon balance. Based on analysis of available data, it appears that over the past decade or so, around 0.07 to 0.18 Gt of carbon has been released to the atmosphere annually. The flux is associated principally with reclamation of Histosols for food production. Opening up of organic soil pools is occurring principally in southeast Asia, where the largest Histosol pools are located. Lower carbon releases, however, also are occurring in Latin America and Africa. The future carbon balance of tropical organic soils will depend to a considerable extent upon the success of recent initiatives to increase yield of agricultural and aquacultural products from previously unutilized organic soils deposits in large wetlands.