Sulfate deposition and temperature controls on methane emission and sulfur forms in peat

Natural wetlands are the single most important contributors of methane (CH₄) to the atmosphere. Recent research has shown that the deposition of sulfate (SO₄^2–) can substantially reduce the emission of this radiatively important gas from wetlands. However, the influence of temperature in regulating the extent of this effect is unclear. Peatlands also constitute an important store of sulfur (S), so understanding the effect of S deposition on S dynamics within this store is important if we are to understand the interaction. The effect of enhanced SO₄^2– deposition on CH₄ fluxes and S pools were investigated in peatland monoliths under controlled environment conditions. This enabled a close examination of effects at the onset of experimentally enhanced SO₄^2– deposition while examining temperature effects on the interaction. Experimentally enhanced S deposition at rates as small as 15 kg SO₄^2–-S ha^–1 year^–1 suppressed CH₄ emissions by 30%. There was no increased suppression at larger deposition rates of simulated acid rain. Temperature affected the suppressive effect of the simulated acid rain. At low temperatures (down to 5 °C), there was a greater proportional suppression than at higher temperatures (up to 20 °C). Evidence suggests that populations of SO₄^2–-reducing bacteria do not respond, as previously thought, to enhanced SO₄^2– supply with a boom followed by a bust and less recalcitrant S pools (SO₄^2– and S°) were depleted in the SO₄^2–-treated peat, indicating enhanced S turnover. A significant proportion of the SO₄^2– from the treatment was taken up and stored as SO₄^2– in vascular plants, placing this mechanism as a potentially important seasonal regulator of peatland SO₄^2– availability.