Peatlands like bogs and fens have been in the spotlight for some time for their role in climate change, both as carbon sinks and as methane sources. Methane is produced naturally in the low-oxygen environments of peatlands and Arctic lakes. It is a potent greenhouse gas that traps heat more effectively than carbon dioxide and poses a threat to agriculture.
Despite its importance to climate patterns, the dynamics of methane production in peatlands are not fully understood. Here Glaser et al. build upon previous studies to analyze 43 years of peatland data and draw out connections between climate patterns and methane dynamics.
The researchers sampled water in pores, or microscopic voids in peat, at numerous sites across the Glacial Lake Agassiz peatlands in northwestern Minnesota to see how water moves solutes through the peat. The researchers took advantage of the calcium-rich deposits that lie beneath the peatland, measuring calcium to trace the upward movement of groundwater in the peat. They examined tritium, a radioactive hydrogen isotope that has been present in the atmosphere since nuclear testing began, to trace the downward movement of precipitation. Finally, they tracked radiocarbon, which is also carried downward by precipitation, as a representative of young, easily altered, and mobile forms of carbon that stimulate methane production.
The researchers identified three periods in the climate of the past century: dry (1911–1940), transitional (1941–1986), and moist (1991–2012). They found that during the dry and transitional phases, contemporary precipitation penetrated only 1 meter into the peat, but by the onset of the moist phase it had flushed the top 2 meters. Because the carbon that stimulates methane production is primarily dissolved organic carbon carried downward through the peat by rainwater rather than the solid-phase carbon that forms peat, this change in transport depth doubled the peak production zones for methane. Methane production is accelerated even more in areas dominated by sedges, grasslike plants that exude more easily altered forms of dissolved organic carbon from their roots.
As climate patterns continue to change, it is important to understand how chemical processes in peatlands change along with them. The researchers suggest that other factors, such as changing peat temperatures or water levels, may also play a role in a peatland’s greenhouse gas emissions. Because the shift in pore water chemistry that doubled methane production zones happened so suddenly and unexpectedly, the researchers warn that peatlands may be even more sensitive to changes in climate patterns than was originally thought. (Global Biogeochemical Cycles, doi:10.1002/2016GB005397, 2016)
—Elizabeth Jacobsen, Staff Writer