HR: 15:25h
AN: B52D-07    [PDF]
TI: Evidence of a Positive Warming Effect on Boreal Productivity Derived From a 11-year Air CO2 Concentration Record at Fraserdale
AU: * Chen, J M
EM: chenj@geog.utoronto.ca
AF: Department of Geography, University of Toronto 100 St. George St., Toronto, Ont M5S 3G3 Canada
AU: Chen, B
EM: chenb@geog.utoronto
AF: Department of Geography, University of Toronto 100 St. George St., Toronto, Ont M5S 3G3 Canada
AU: Liu, J
EM: jliu@atmosp.physics.utoronto.ca
AF: Department of Physics, University of Toronto 60 St. George St., Toronto, Ont M5S 1A7 Canada
AU: Higuchi, K
EM: kaz.higuchi@ec.gc.ca
AF: Meteorological Service of Canada, 4905 Dufferin Street, Toronto, Ont M3H 5T4 Canada
AU: Chan, D
EM: douglas.chan@ec.gc.ca
AF: Meteorological Service of Canada, 4905 Dufferin Street, Toronto, Ont M3H 5T4 Canada
AU: Shashkov, A
EM: alexander.shashkov@ec.gc.ca
AF: Meteorological Service of Canada, 4905 Dufferin Street, Toronto, Ont M3H 5T4 Canada
AU: Huang, L
EM: lin.huang@ec.gc.ca
AF: Meteorological Service of Canada, 4905 Dufferin Street, Toronto, Ont M3H 5T4 Canada
AU: Worthy, D
EM: doug.worthy@ec.gc.ca
AF: Meteorological Service of Canada, 4905 Dufferin Street, Toronto, Ont M3H 5T4 Canada
AB: An 11-year long (1990-1996, 1999-2002), hourly air CO$_{2}$ concentration record measured on a 40-m tower at Fraserdale, northern Ontario, is used to retrieve information on the carbon cycle of boreal ecosystems at the landscape level. Using a model, the effects of ecosystem metabolism and atmospheric diffusion on the hourly CO$_{2}$ concentration are separated, and daily ecosystem respiration (R$_{e}$) and gross primary productivity (GPP) are estimated. Both R$_{e}$ and GPP increased with increasing air temperature. As the mean air temperature in the growing season (May to October) varied from 10.6 to $13.2\deg$C within the 11-year period, seasonal mean GPP varied from 3.4 to 5.3 gC m$^{-2}$d$^{-1}$ and R$_{e}$ from 3.2 to 3.9 gC m$^{-2}$d$^{-1}$. The temperature sensitivity is higher for GPP than for R$_{e}$ because of additive direct and indirect warming effects on productivity. Faster nutrient mineralization in soil at higher temperatures is considered to be the main indirect factor according to model simulations. As the footprint area of the concentration measurements is of the order of 10$^{2}$-10$^{4}$ km$^{2}$, the methodology allows for evaluation of the collective effects of climate change on ecosystems at the landscape level consisting of forests of different ages, species and densities as well as non-forest cover types. The atmospheric diffusion model only considers the vertical diffusion processes in the surface and mixed layers in both daytime unstable and nighttime stable conditions. In hourly simulations, such a model is in error under advection conditions associated with synoptic weather systems, but when averaged for ten-day periods, the error in the simulated CO$_{2}$ is less than 0.6 ppmv. The methodology of deriving fluxes from concentration was tested against a tower flux site in a black spruce forest in Saskatchewan for the year 1998. The correlation coefficient was 0.86 between concentration-derived daily GPP and those derived from eddy covariance flux measurements. When averaged for 10 days, the coefficient increased to 0.94.
UR: http://www.geog.utoronto.ca/info/facweb/Chen/Chen%27s%20homepage/home.htm
DE: 0315 Biosphere/atmosphere interactions
DE: 0330 Geochemical cycles
DE: 1610 Atmosphere (0315, 0325)
DE: 1615 Biogeochemical processes (4805)
DE: 3307 Boundary layer processes
SC: Biogeosciences [B]
MN: 2003 Fall Meeting