"The extensive deposits of peat in Canada are an important natural resource, but one that is being disturbed more often, not only by wildfire but also by human activities," Turetsky said. Previous studies have documented the effects of land use practices and global warming on the ecology of peatlands. "But we wanted to examine how decades of lowered water table in peatlands might affect wildfire behaviour, and that required a very large experiment."
To determine those effects, the researchers used a unique outdoor laboratory. A large section of a boreal fen near Slave Lake, Alta., had been drained over 20 years ago in a wetland drainage project. A portion of the fen including drained and pristine plots burned in a wildfire in 2001 allowed for a natural experiment.
Earlier research had documented increases in tree growth and carbon storage after drainage. "But nobody had looked at the impacts of dewatering on fire intensity and associated carbon gains or losses," Donohue said.
The results were surprising, he said. Long-term drainage actually increased tree productivity and carbon storage in the fen soils. But the lower water table also changed wildfire conditions, and losses of soil carbon to burning in the drained areas increased ninefold.
"Even though the organic matter accumulation doubled over two decades after drainage, severe burning triggered the complete loss of this newly stored carbon, plus a further 450 years' worth of peat accumulation," Donahue said.
"Currently, peatlands are considered important global stores for carbon. But we've shown that human disturbance or climate-induced drying can switch peatlands from sinks to potentially huge sources of carbon, with losses associated with severe burning far outweighing long-term rates of sequestration."
|Contact: Prof. Merritt Turetsky, University of Guelph|
University of Guelph