Methane emissions from trees planted on a closed landfill site

Area of Science:

• Environmental Science
• Ecology
• Biogeochemistry

Background:

• Trees possess adaptations enabling subterranean methane (CH4) to bypass soil oxidation.
• The role of these adaptations in landfill environments, where trees may influence CH4 emissions, remains unquantified.

Purpose of the Study:

• To measure greenhouse gas (GHG) emissions, specifically CH4 and CO2, from tree stems and soils in a landfill setting.
• To compare these emissions with those from a natural, non-landfill site.
• To determine the contribution of tree stem emissions to the overall CH4 flux from a landfill surface.

Main Methods:

• Utilized off-axis integrated cavity output spectroscopy (OAICOS) and flux chambers for GHG measurements.
• Monitored CH4 and CO2 emissions from tree stems and soils at a closed UK landfill and a comparable natural site.
• Analyzed seasonal variations and differences across stem heights and tree species.

Main Results:

• Average CH4 stem fluxes were significantly higher at the landfill site (31.8 µg m-2 h-1) compared to the natural site (-0.3 µg m-2 h-1).
• Seasonal patterns in CH4 and CO2 stem emissions were observed at the landfill, but not significantly influenced by stem height or tree species.
• Tree stem emissions represented 39% of the total CH4 surface flux and 7% of the CO2 surface flux at the landfill.

Conclusions:

• Tree stems are a significant pathway for CH4 release from landfills, accounting for a substantial portion of the total surface flux.
• This previously unrecognized pathway must be incorporated into future landfill carbon assessments and climate models.
• Understanding these biophysical processes is crucial for accurate environmental monitoring and management of landfill sites.