Indonesian tropical peatlands — Carbon sink faces crisis of collapse

A research group including Senior Principal Researcher Jun Koarashi and Principal Researcher Mariko Andoh of the Nuclear Science and Engineering Center, the Nuclear Science Research Institute at the Japan Atomic Energy Agency (JAEA), in joint research with Kyoto University, Hokkaido University, and the Center for International Cooperation in Sustainable Management of Tropical Peatland at the University of Palangka Raya (Indonesia), clarified that 800 million to 3.7 billion tons of carbon accumulated in peat was emitted due to agricultural land conversion and subsequent fires in the tropical peatlands of Central Kalimantan, Indonesia. They found that carbon stored in tropical peatlands is extremely vulnerable to human activities. This is expected to contribute to the promotion of climate change countermeasures. The results were published in Nature Communications on May 27.

Tropical peatlands account for only 0.3% of the earth's land area, but their carbon storage reaches 105 billion tons, which accounts for 6% of the world's soil carbon storage. Under conditions of a high groundwater table, peat soil is covered with water and has little oxygen. The decomposition of organic plant matter does not progress, and it accumulates over thousands of years. Carbon was stored as a solid, and forests grew to form peat swamp forests. However, with the population growth since the 1990s, development in Southeast Asia has progressed, and large-scale drainage has been carried out through farmland conversion and other activities. This has promoted microbial decomposition and made peat fires more likely to happen. On the other hand, the extent of the impact of such human activities on the disturbance of peat swamp forests was not clear.

Therefore, in this research, targeting a representative tropical peatland in Kalimantan Province, the group investigated the long-term carbon accumulation history using the radiocarbon dating method in three environments with different degrees of disturbance: (1) a nearly natural peat swamp forest, (2) a peat swamp forest drained since 1996, and (3) a former peat swamp forest that has had repeated fires after drainage since 1996. The three sites are located within a 15-kilometer radius. In the survey, peat layers were sampled at various depths in 2014.

To evaluate the impact of drainage, they compared (1) and (2). In (2), peat up to 1,000 years old decreased (5 to 11 kg per square meter) due to drainage, and accumulated carbon corresponding to about 200 to 500 years disappeared. Also, in (3), peat up to the past 3,000 years was burned away by fires. Through comparisons with (2), it was estimated that 23 to 32 kg of carbon per square meter was released as CO₂.

It is estimated that these peat swamp forests, which functioned as carbon sinks, turned into emission sources due to these human activities and other factors. The deep peat exposed to the atmosphere by fires is expected to continue further release through microbial decomposition.

Applying the obtained results to the entire tropical peatlands of Indonesia, it is estimated that 800 million to 3.7 billion tons of carbon were emitted during the same period due to drainage and fires, in addition to normal emissions.

Koarashi stated: "Because the evaluation method of this study can visualize the carbon emissions of peatlands that are difficult to see, we hope to contribute to the conservation and restoration of peatlands and the establishment of measures to suppress carbon emissions. Locally, backfilling drainage channels is also being considered, and we expect that our method can be used for evaluation at that time as well."

Journal Information
Publication: Nature Communications
Title: Progressive release of long-stored carbon from tropical peatland disturbances
DOI: 10.1038/s41467-026-72890-y