Effects of decadal deposition of nitrogen and sulfur, and increased temperature, on methane emissions from a boreal peatland

Boreal peatlands represent a significant source of methane to the atmosphere. Pollutants and climate changes resulting from human activity are likely to affect the processes controlling methane emissions from these systems. This study investigated the effects of decadal deposition of nitrogen and sulfate, and increased air temperature, on methane emissions from a northern Swedish peatland during the snow‐free seasons of 2005 and 2006, the latter being exceptionally dry. The experimental setup involved a full factorial design at two levels with greenhouse cover (present or absent), nitrogen deposition (2 or 30 kg N ha−1 a−1), and sulfate deposition (3 or 20 kg S ha−1 a−1) as experimental factors. Methane emission rates were measured using static chambers after 10–11 years of experimental manipulations. Emissions were significantly reduced by the greenhouse treatment in 2005, by 30% on average, but not in 2006. The reduction in methane emissions in response to the greenhouse treatment were counteracted by nitrogen deposition; with high nitrogen deposition the effect of the greenhouse cover was low and nonsignificant. High nitrogen deposition increased methane emissions at ambient sulfate levels, probably due to sedge cover increasing from 37 to 65%, but the combination of high nitrogen deposition and high sulfate deposition did not affect methane emissions. Effects of increased nitrogen on methane emission have previously in short‐term manipulations (