Deforested tropical peatlands are haemorrhaging carbon from deep within their peat soils, with consequences for the release of carbon dioxide to the atmosphere, according to new research published in Nature.
The research was carried out by scientists at the Open University and partners, the Centre for Ecology & Hydrology (CEH), the University of Leicester, the NERC Radiocarbon Facility, Bangor University, Deltares, the Met Office and the University of Plangka Raya, Indonesia.
Tropical peatlands, with their high water tables and low decomposition rates, form vast stores of organic carbon tens of metres thick. Most of it is found in Indonesia, where the natural swamp forests (also home to endangered animal species such as orangutans) are increasingly being destroyed by deforestation, drainage and fire, to make way for agriculture, in particular oil palm for biofuels and food.
Dr Sam Moore, lead author of the study and former Open University PhD student, said, “We measured carbon losses in channels draining intact and deforested peatlands, and found it is 50 per cent higher from deforested swamps, compared to intact swamps. Dissolved organic carbon released from intact swamps mainly comes from fresh plant material, but carbon from the deforested swamps is much older – centuries to millennia – and comes from deep within the peat column.”
Co-author Professor Chris Evans from CEH led the work on radiocarbon dating of dissolved organic carbon (DOC). He said, "We found that the DOC being released by the drained peat swamps was up to 4000 years old - as far as we know the oldest measurement of this type ever recorded - which tells us that carbon which has been securely stored for millennia is now being released by drainage for agriculture and biofuels. Most of this carbon will probably end up in the atmosphere as carbon dioxide, contributing to climate change."
Deforestation of Asian peat swamps is an important source of carbon dioxide emissions globally and its emission may be larger than previously thought. Carbon dating shows that the additional carbon lost from deforested swamps comes from peat which had been securely stored for thousands of years. Carbon lost from the drainage systems of deforested and drained peatlands is often not considered in ecosystem exchange carbon budgets, but the research team found it increased the estimated total carbon loss by 22 per cent.
Changes in the water cycle seem to be the principal driver of this increase in carbon loss. Much of the water falling as rain would normally leave the ecosystem through transpiration in vegetation, but deforestation forces it to leave through the peat, where it dissolves fossil carbon on its way.
Dr Vincent Gauci, Senior Lecturer in Earth Systems and Ecosystem Science at The Open University, and corresponding author said: “Essentially, ancient carbon is being dissolved out of Asian peatlands as they are increasingly being turned over to agriculture to meet global demands for food and biofuels. This has led to a large increase in carbon loss from Southeast Asian rivers draining peatland ecosystems - up by 32 per cent over the last 20 years, which is more than half the entire annual carbon loss from all European peatlands. The destruction of the Asian peat swamps is a globally significant environmental disaster, but unlike deforestation of the Amazon, few people know that it is happening.”
The authors concluded that their results increase the urgency for protecting these ecosystems from ongoing destruction for oil palm and other uses.
Professor Chris Evans is currently contributing to the development, by the Intergovernmental Panel on Climate Change (IPCC), of new guidelines for reporting greenhouse gas emissions from drained and re-wetted peatlands. The data from this study, as well as ongoing CEH measurements in the UK within our Carbon Catchments programme, have allowed waterborne carbon losses to be included in these emissions for the first time.
Deep instability of deforested tropical peatlands revealed by fluvial organic carbon fluxes is published in Nature (doi:10.1038/nature11818).
The Open University issued a press release about this paper.