Methane and nitrous oxide exchange over a managed hay meadow

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Ecology

Background:

• Temperate grasslands play a role in the global carbon cycle, but their greenhouse gas (GHG) exchange, particularly methane (CH4) and nitrous oxide (N2O), is not fully understood.
• Accurate assessment of GHG budgets for managed ecosystems requires quantifying emissions of CH4 and N2O alongside carbon dioxide (CO2) sequestration.

Purpose of the Study:

• To quantify the exchange rates of methane (CH4) and nitrous oxide (N2O) in a temperate mountain grassland.
• To determine the annual net GHG balance of the grassland, considering CO2, CH4, and N2O fluxes.
• To identify environmental factors influencing CH4 and N2O fluxes and assess the challenges in their measurement and interpretation.

Main Methods:

• Utilized the eddy covariance method to measure CH4 and N2O fluxes over a 22-month period (2010-2012).
• Analyzed the influence of ancillary parameters (e.g., soil moisture, temperature) on gas flux variability.
• Compared CH4 and N2O flux measurements with CO2, H2O, and energy fluxes.

Main Results:

• The grassland was a net annual source of both CH4 and N2O, despite being a sink during certain periods.
• CH4 and N2O emissions offset a significant portion (55%) of the grassland's CO2 sink strength in 2011.
• N2O emissions peaked at intermediate soil water content and specific soil temperatures (near 0°C or >14°C).
• Flux interpretation was challenging due to footprint heterogeneity and measurement uncertainties.

Conclusions:

• Temperate managed grasslands, even those with seemingly optimal conditions, can be significant sources of CH4 and N2O.
• The contribution of CH4 and N2O to the overall GHG balance of grasslands cannot be neglected.
• Accurate GHG assessments require comprehensive monitoring of all relevant greenhouse gases, not just CO2.