HR: 09:45h
AN: B21D-08 INVITED    [Abstracts]
TI: Measurement of Landscape-scale Fluxes in the Complex Terrain of a Rocky Mountain Subalpine Forest
AU: * Monson, R K
EM: Russell.Monson@colorado.edu
AF: Department of Ecology and Evolutionary Biology and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, United States
AU: Turnipseed, A
EM: turnip@ucar.edu
AF: Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO 80307, United States
AU: Sun, J
EM: jsun@ucar.edu
AF: Mesoscale and Microscale Meteorology Division, National Center for Atmospheric Research, Boulder, CO 80307, United States
AU: Anderson, D
EM: deander@usgs.gov
AF: Water Resources Division, US Geological Survey, Lakewood, CO 80225, United States
AU: Yi, C
EM: Chuixiang.Yi@colorado.edu
AF: Department of Ecology and Evolutionary Biology and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, United States
AU: Burns, S
EM: Sean.Burns@colorado.edu
AF: Department of Ecology and Evolutionary Biology and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, United States
AU: Burns, S
EM: Sean.Burns@colorado.edu
AF: Mesoscale and Microscale Meteorology Division, National Center for Atmospheric Research, Boulder, CO 80307, United States
AU: Lamb, B
EM: blamb@wsu.edu
AF: Laboratory for Atmospheric Research, Washington State University, Pullman, WA 99164, United States
AU: Schimel, D
EM: schimel@ucar.edu
AF: NEON, Inc., 1444 I St., NW, Washington, D.C 20005, United States
AB: For the past eight years, we have made observations using various approaches, including eddy covariance, mass-balance budgeting of advective fluxes, dispersion of SF6 tracer, and energy-budget closure to evaluate landscape-scale fluxes of CO2, H2O and energy in a complex mountain landscape in the Colorado Rocky Mountains. We discovered that daytime energy budget closure using eddy covariance fluxes balanced by available net radiation was better than 84% on a half-hourly basis in both winter and summer, and approached complete closure at surface friction velocities (u*) greater than 1 m s-1. Co-spectral analysis indicated that contributions from advective fluxes and low-frequency flux contributions were likely responsible for the lack of daytime energy budget closure at lower u*. Using multiple towers dispersed across a restricted (0.25 km2) footprint of the landscape we discovered that the highest nighttime CO2 concentrations occur at the lowest point (stream channel), due to the forces of gravitational drainage flows, that the downslope drainage of high-CO2 air is broken up gradually in the late morning when within canopy turbulence increases, and that there is likely photosynthetic assimilation of 'pooled' CO2 the next morning when upslope flows develop due to mountainside warming. Studies of nighttime dispersion of released SF6 tracer showed that the nighttime drainage flows are restricted to a relatively shallow layer of air beneath the canopy, with little vertical mixing. We used the multiple towers to estimate the contributions to the local CO2 budget by horizontal and vertical advective fluxes (driven by the nighttime drainage flows) and found that compared to traditional methods of correcting eddy covariance derived CO2 budgets on flat terrain, the complex terrain in at the Niwot Ridge site can induce an average 10% error in monthly cumulative net ecosystem exchange (NEE), which is amplified to a 65% error in cumulative NEE across six years. Thus, the errors to the local CO2 budget, when advective fluxes are ignored can be large. We developed the concept of a mountain 'carbonshed' to describe the effects of complex terrain on local CO2 budgets; the carbonshed is potentially a valuable concept that represents an organizing feature for studying landscape-scale fluxes in mountain-valley systems.
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0428 Carbon cycling (4806)
DE: 1631 Land/atmosphere interactions (1218, 1843, 3322)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting