HR: 0830h
AN: B41C-0886    [PDF]
TI: Carbon and Nitrogen Trace Gas Fluxes from Urban Grasslands in California
AU: * Chou, W W
EM: wchou@nature.berkeley.edu
AF: University of California Berkeley, 151 Hilgard Hall MC #3110, Berkeley, CA 94720 United States
AU: Silver, W L
EM: wsilver@nature.berkeley.edu
AF: University of California Berkeley, 151 Hilgard Hall MC #3110, Berkeley, CA 94720 United States
AB: Human management of urban ecosystems affects their biogeochemical cycling by altering environmental conditions such as water and resource availability. Urban grasslands under human-modified regimes comprise approximately 10 million hectares in the United States and represent a poorly quantified biogenic source of radiatively active trace gases from soil. We described the annual pattern of net CO$_{2}$, N$_{2}$O, and CH$_{4}$ soil effluxes and associated soil C and N pools and fluxes for urban grasslands in Berkeley, California, USA. Using a static chamber approach, we undertook a 12-month field study of 6 irrigated and fertilized lawns dominated by grasses of either C3 or C4 photosynthetic systems. The urban grasslands emitted 36($\pm$4) Mg C ha$^{-1}$ yr$^{-1}$ as CO$_{2}$, more than 7 times the rate observed from natural grasslands globally. Lawns dominated by C4 species emitted significantly greater amounts of CO$_{2}$ on average relative to C3-dominated lawns. Rates of CO$_{2}$ efflux from the urban grasslands showed a strong response to ambient temperature, and urban grasslands emitted higher CO$_{2}$ fluxes during warm summer months when unmanaged grassland ecosystems in this Mediterranean climate would exhibit low to no activity due to drought. Fluxes of N$_{2}$O and CH$_{4}$ were generally negligible. The exception was a large and significant release of N$_{2}$O associated with the construction of a new lawn. In this site we measured a maximum rate of N$_{2}$O emissions of 877 ($\pm$244) ng N cm$^{-2}$ h$^{-1}$ and an average rate of 290 ($\pm$41) ng N cm$^{-2}$ h$^{-1}$ over a 6.5-week period. The observation of higher trace gas losses from urban grasslands relative to natural systems encourages further examination to determine their role as sources of greenhouse gases.
DE: 0315 Biosphere/atmosphere interactions
DE: 0400 Biogeosciences
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting