14.1 Magnitudes and Multi-year Trends of Greenhouse Gas Fluxes in the Denver, Colorado Urban Ecosystem

Friday, 6 August 2010: 11:15 AM
Crestone Peak I & II (Keystone Resort)
Dean E. Anderson, U.S. Geological Survey, Denver, CO; and K. Powell and G. Szanko

Recent reports indicate that, in the U.S., nearly 78% of fossil fuel emissions occur in urban areas along with 60% of residential water use. Urban areas also contain the largest irrigated crop by area- lawns. Urban lawns cover about 30% of Denver and tree cover averages about 12%. Measurements of greenhouse gas (GHG) fluxes (carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O)) in cities have been rare. We report net ecosystem exchange (NEE) rates of CO2 measured from a tall tower using eddy covariance and storage flux methods in Denver during 2001-2007 and include GHG fluxes over lawns and water bodies in parks using chambers. A separate continuously running eddy covariance station was used to estimate NEE of CO2 in one of the parks in the tall tower footprint. Following best practices (watering and fertilizing) lawns, with a leaf area index averaging about 2.5, annually sequester 1.5+/-.3 Ton C per hectare and emit 1.5 +/-0.8 kg N2O-N per hectare. CH4 fluxes were negligible. There are 83 ponds or lakes larger than 1ha in the Denver urban ecosystem, 24 of which were sampled from fall 2008 to summer 2009. All but one water body was supersaturated (with respect to the atmosphere) with CH4, 22 were supersaturated with N2O and 21 with CO2. Calculation of emission rates from these water bodies is underway. NEE and CO2 concentration measured from the tall tower indicated a strong dependence on fetch, time of day, day of the week, and season that indicate impacts of environmental and anthropogenic influences.
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