HR: 09:30h
AN: B31C-07    [Abstracts]
TI: Quantifying Urban-Ecosystem Atmosphere Fluxes of N$_2$O, CO$_2$, CH$_4$ over Denver, Colorado.
AU: * Anderson, D E
EM: deander@usgs.gov
AF: U.S. Geological Survey, M.S. 413, Federal Center, Denver, CO 80225 United States
AU: Tindall, J
EM: jtindall@usgs.gov
AF: U.S. Geological Survey, M.S. 413, Federal Center, Denver, CO 80225 United States
AU: Thienelt, T
AF: U.S. Geological Survey, M.S. 413, Federal Center, Denver, CO 80225 United States
AB: Urban ecosystems are complex, rapidly expanding, and the location of strong emissions of greenhouse gases. Ecosystem-atmosphere exchanges of carbon dioxide (CO$_2$), methane (CH$_4$), nitrous oxide (N$_2$O) and water vapor were measured over a ~30 km$^2$ portion of Denver, Colorado. Equipment used in these measurements included eddy covariance sensors at two levels on a tall 120m tower for CO$_2$ flux and evapotranspiration (ET), soil surface chambers for the measurement of CO$_2$, CH$_4$, and N$_2$O fluxes at 33 locations, and direct flux measurements of CO$_2$ and N$_2$O from the water treatment system. Measurement of CO$_2$ flux and ET has been continuous for more than two years (2002-2004). Chamber measurements were conducted on selected dates during two growing seasons. Direct flux measurements from the water treatment system were conducted on a monthly basis in the 2004 summer. Measurements indicate both strong temporal and spatial heterogeneity of fluxes owing to characteristics of natural and anthropogenic ecosystem components. Tower-based eddy covariance measurements indicated that the urban ecosystem was a net CO$_2$ source when measurements were averaged over a day or longer. However, during the majority of mid-day summer hours it was a weak sink, sequestering atmospheric CO$_2$. In this case, the weak sink may indicate that the vegetative sink for CO$_2$ was stronger than anthropogenic emissions of CO$_2$ from heavy traffic on nearby highways in the flux footprint. Chamber-based measurements of CH$_4$ flux over most dry land surfaces with vegetation varied from -0.3 to 2.6mmol/m$^2$/d while the range in N$_2$O flux was ~0 to 0.2\mu mol/m$^2$/d. For both fluxes, the higher values were observed over wet soils ($>$20%, volumetric). In contrast, at certain locations over a landfill (closed more than 30years ago) and converted to other uses (light industry, city park and golf course), CO$_2$, CH$_4$ and N$_2$O fluxes were a few orders of magnitude higher than that found anywhere else in the city. However, for the majority of the landfill surface, fluxes were near that found elsewhere in the city. N$_2$O flux from a waste water treatment facility within the study area was 3.2X10$^5$ mol/yr or about 1 mol/yr/capita. This does not include emissions from waste water in transit to the waste water treatment facility or departing it. There will also be discussion of other significant sources of N$_2$O within the urban ecosystem.
DE: 1615 Biogeochemical processes (4805)
DE: 0315 Biosphere/atmosphere interactions
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting