Influence of Land Cover and Climate on CO2 and CH4 fluxes from Urban Soils

Abstract:

Soils are important sinks for greenhouse gases globally. Urbanization influences biogeochemical processes and gas fluxes through increased nitrogen deposition, heat island effects, and vegetation management. Previous work at the Baltimore Ecosystem Study LTER site has reported elevated CO₂ fluxes and reduced CH₄ consumption in urban soils. Differences among soils (urban forest, rural forest, lawns) have been linked to nitrogen cycling and may also be driven by temperature differences between land cover types. A combination of site-specific changes (land cover, nitrogen availability) and climatological (temperature, soil moisture) factors are likely to influence long-term patterns in gas fluxes and therefore carbon storage in growing urban regions. We utilized 15 years of measured gas fluxes and continuous temperature and soil moisture data to model CO₂ emissions and CH₄ consumption under different vegetation classes. We scaled these fluxes to the metropolitan region using high-resolution spatial, and found that regional CH₄ consumption and CO₂ fluxes are sensitive to changes in temperature and land cover. For instance, in 2007 land cover in Baltimore City had 21% lawn and 22% forest cover. If all of the lawn area in the city were converted to urban forest, CH₄ consumption by urban soils would increase by 70% and CO₂ emissions would decrease by 20%. In suburban Baltimore County, lawns and urban forests comprised 35 and 50% of land cover respectively. If all lawns in the county were converted to urban forest, soil CH₄ consumption would increase by 55% and soil CO₂ flux would decrease by 20%. Soil CO₂ fluxes also increase by approximately 0.1g C m^-2 d^-1 for every 1° C increase across all land cover classes. CH₄ consumption increases with temperature in urban and rural forest soils. Our results highlight the interacting effects of land cover change and climate on carbon fluxes from urban soils.