Methane uptake in urban forests and lawns

Area of Science:

• Environmental Science
• Soil Science
• Ecology

Background:

• Methane (CH4) is a potent greenhouse gas with significant natural sinks in soil bacteria.
• Soil CH4 consumption is sensitive to nitrogen (N) deposition and soil conditions.
• Urbanization alters ecosystems, potentially impacting regional methane budgets.

Purpose of the Study:

• To evaluate the effects of urban land use and atmospheric changes on CH4 uptake.
• To compare CH4 fluxes in urban forests, rural forests, and urban lawns.
• To assess the significance of urban CH4 uptake changes relative to other greenhouse gas forcings.

Main Methods:

• Monthly measurements of CH4 fluxes over four years (2001-2005).
• Comparison of CH4 uptake in urban forest, rural forest, and urban lawn plots in Baltimore, MD.
• Analysis of potential mechanisms reducing CH4 uptake in urban environments.

Main Results:

• Rural forests exhibited high CH4 uptake capacity (1.68 mg m(-2) day(-1)).
• CH4 uptake was substantially reduced in urban forests (0.23 mg m(-2) day(-1)).
• CH4 uptake was nearly eliminated in urban lawns.

Conclusions:

• Conversion of native ecosystems to urban lawns drastically reduces methane uptake.
• Increased nitrogen deposition, CO2 levels, and altered soil conditions may explain reduced CH4 uptake.
• While significant locally, these reductions in CH4 uptake do not appear to significantly impact statewide greenhouse gas forcing.