How does elevated ozone reduce methane emissions from peatlands?

Area of Science:

• Environmental Science
• Ecology
• Atmospheric Chemistry

Background:

• Tropospheric ozone (O3) pollution is increasing globally.
• Its impact on methane (CH4) emissions from peatlands is not well understood.
• Peatlands are significant sources of atmospheric CH4.

Purpose of the Study:

• To investigate the effects of elevated ozone on CH4 emissions from temperate peatlands.
• To elucidate the mechanisms driving O3-induced changes in CH4 flux.
• To assess the role of plant carbon and soil nitrogen.

Main Methods:

• Peatland mesocosms were exposed to varying O3 concentrations in open-top chambers for 2.5 years.
• CH4 emissions, root biomass, dissolved organic carbon, and soil inorganic nitrogen were measured.
• CH4 production and oxidation potentials were assessed.

Main Results:

• Summer daytime O3 exposure (35ppb) reduced CH4 emissions by 27%.
• No significant effects were observed with year-round lower O3 concentrations (10-25ppb).
• Reduced CH4 emissions correlated with decreased pore water ammonium, not changes in plant carbon inputs.

Conclusions:

• Elevated summer O3 can decrease temperate peatland CH4 emissions.
• The primary mechanism involves reduced soil inorganic nitrogen affecting methanogenesis and/or methanotrophy.
• Future O3 increases may alter peatland CH4 budgets, but effects depend on O3 concentration and seasonality.