Comparisons were made among Douglas-fir forest, aspen (broad leaf deciduous) forest and wheatgras... more Comparisons were made among Douglas-fir forest, aspen (broad leaf deciduous) forest and wheatgrass (C3) grassland for ecosystem-level water-use efficiency (WUE). WUE was defined as the ratio of photosynthetic CO2 assimilation rate and evapotranspiration (ET) rate. The ET data measured by eddy covariance were screened so that they overwhelmingly represented transpiration. The three sites used in this comparison spanned a range of vegetation (plant functional) types and environmental conditions within western Canada. When compared in the relative order Douglas-fir (located on Vancouver Island, BC), aspen (northern Saskatchewan), grassland (southern Alberta), the sites demonstrated a progressive decline in precipitation and a general increase in maximum air temperature and atmospheric saturation deficit (Dmax) during the mid-summer. The average (±SD) WUE at the grassland site was 2.6±0.7 mmol mol−1, which was much lower than the average values observed for the two other sites (aspen: 5.4±2.3, Douglas-fir: 8.1±2.4). The differences in WUE among sites were primarily because of variation in ET. The highest maximum ET rates were approximately 5, 3.2 and 2.7 mm day−1 for the grassland, aspen and Douglas-fir sites, respectively. There was a strong negative correlation between WUE and Dmax for all sites. We also made seasonal measurements of the carbon isotope ratio of ecosystem respired CO2 (δR) in order to test for the expected correlation between shifts in environmental conditions and changes to the ecosystem-integrated ratio of leaf intercellular to ambient CO2 concentration (ci/ca). There was a consistent increase in δR values in the grassland, aspen forest and Douglas-fir forest associated with a seasonal reduction in soil moisture. Comparisons were made between WUE measured using eddy covariance with that calculated based on D and δR measurements. There was excellent agreement between WUE values calculated using the two techniques. Our δR measurements indicated that ci/ca values were quite similar among the Douglas-fir, aspen and grassland sites, despite large variation in environmental conditions among sites. This implied that the shorter-lived grass species had relatively high ci/ca values for the D of their habitat. By contrast, the longer-lived Douglas-fir trees were more conservative in water-use with lower ci/ca values relative to their habitat D. This illustrates the interaction between biological and environmental characteristics influencing ecosystem-level WUE. The strong correlation we observed between the two independent measurements of WUE, indicates that the stable isotope composition of respired CO2 is a useful ecosystem-scale tool to help study constraints to photosynthesis and acclimation of ecosystems to environmental stress.
The anisotropic and skewed turbulent motions on a broad scale range contribute to the complexity ... more The anisotropic and skewed turbulent motions on a broad scale range contribute to the complexity of dispersion patterns in the atmospheric convective boundary layer (CBL). The main turbulence forcing in the CBL is the convective heat transfer from a warm underlying surface. Several field, numerical and laboratory studies, see eg.
Carbon dioxide, water vapour, and energy fluxes vary spatially and temporally within forested env... more Carbon dioxide, water vapour, and energy fluxes vary spatially and temporally within forested environments. However, it is not clear to what extent they vary as a result of variability in the spatial distribution of biomass and elevation. The following study presents a new methodology for extracting changes in the structural characteristics of vegetation and elevation within footprint areas, for direct comparison with eddy covariance (EC) CO2 flux concentrations. The purpose was to determine whether within-site canopy structure and local elevation influenced CO2 fluxes in a mature jack pine (Pinus banksiana Lamb.) forest located in Saskatchewan, Canada. Airborne light detection and ranging (lidar) was used to extract tree height, canopy depth, foliage cover, and elevation within 30 min flux footprints. Within-footprint mean structural components and elevation were related to 30 min mean net ecosystem productivity (NEP) and gross ecosystem production (GEP). NEP and GEP were modeled u...
Background/Question/Methods: Eddy covariance (EC) observations of ecologically relevant trace gas... more Background/Question/Methods: Eddy covariance (EC) observations of ecologically relevant trace gas and energy fluxes are too sparse spatially for direct assimilation into gridded earth system models (ESMs) or for comparison with large-scale observations. The spatial coverage of a tower EC measurement may represent less than 1% of the domains typically covered by ESMs and remote sensing data. It is hence desirable to improve the spatial representativeness and temporal consistency of EC measurements for improving ecological inference. The objectives of this study are (i) to provide consistent flux time-series for target regions, rather than for a spatio-temporally variable patch of surface close to tower sites, and (ii) to test the applicability of the presented procedure across eco-climatological gradients covering some of the complexity of NEON sites. Based on the environmental response function approach (ERF, Metzger et al., 2013), we developed a procedure to produce spatio-temporal...
A newly developed pulsed cavity ring-down spectroscopy (CRDS) system for measuring atmospheric ga... more A newly developed pulsed cavity ring-down spectroscopy (CRDS) system for measuring atmospheric gaseous elemental mercury (GEM) concentrations at high temporal resolution (25 Hz) was used to successfully conduct the first eddy covariance (EC) flux measurements of GEM. GEM is the main gaseous atmospheric form, and quantification of bidirectional exchange between the Earth's surface and the atmosphere is important because gas exchange is important on a global scale. For example, surface GEM emissions from natural sources, legacy emissions, and re-emission of previously deposited anthropogenic pollution may exceed direct primary anthropogenic emissions. Using the EC technique for flux measurements requires subsecond measurements, which so far has not been feasible because of the slow time response of available instrumentation. The CRDS system measured GEM fluxes, which were compared to fluxes measured with the modified Bowen ratio (MBR) and a dynamic flux chamber (DFC). Measurements...
zip file contains documentation and a file in netcdf format with vegetation height distributions ... more zip file contains documentation and a file in netcdf format with vegetation height distributions between 0 and 70 m at 0.5 m intervals and at 0.5 by 0.5 degrees resolution. analysis is extended to 80 degrees N (previously to 60 degrees N).
Seven years of turbulent flux measurements from the Southern Old Aspen site in Saskatchewan, Cana... more Seven years of turbulent flux measurements from the Southern Old Aspen site in Saskatchewan, Canada, were analyzed to quantify the effect of systematic biases of data processing on half-hourly fluxes as well as annual estimates of net ecosystem production (NEP). Recently, efforts have intensified to unify the processing of half-hourly fluxes as well as annual carbon sequestration across flux tower
Soil water content can exert an important control on tree growth processes, an important consider... more Soil water content can exert an important control on tree growth processes, an important consideration for the boreal forest in Central Canada where climate change may bring about increased drought frequency. Empirical evidence has shown the strong coupling between conductance and photosynthesis, and the effect that drought can have on both variables. In models, canopy conductance and carbon uptake are
For the present study, we derived a footprint climatology for the Southern Old Aspen, Southern Ol... more For the present study, we derived a footprint climatology for the Southern Old Aspen, Southern Old Black Spruce, and Southern Old Jack Pine sites for the years 2005 to 2008. For each 30-min averaged sample period, the footprint area has been calculated taking into ...
Comparisons were made among Douglas-fir forest, aspen (broad leaf deciduous) forest and wheatgras... more Comparisons were made among Douglas-fir forest, aspen (broad leaf deciduous) forest and wheatgrass (C3) grassland for ecosystem-level water-use efficiency (WUE). WUE was defined as the ratio of photosynthetic CO2 assimilation rate and evapotranspiration (ET) rate. The ET data measured by eddy covariance were screened so that they overwhelmingly represented transpiration. The three sites used in this comparison spanned a range of vegetation (plant functional) types and environmental conditions within western Canada. When compared in the relative order Douglas-fir (located on Vancouver Island, BC), aspen (northern Saskatchewan), grassland (southern Alberta), the sites demonstrated a progressive decline in precipitation and a general increase in maximum air temperature and atmospheric saturation deficit (Dmax) during the mid-summer. The average (±SD) WUE at the grassland site was 2.6±0.7 mmol mol−1, which was much lower than the average values observed for the two other sites (aspen: 5.4±2.3, Douglas-fir: 8.1±2.4). The differences in WUE among sites were primarily because of variation in ET. The highest maximum ET rates were approximately 5, 3.2 and 2.7 mm day−1 for the grassland, aspen and Douglas-fir sites, respectively. There was a strong negative correlation between WUE and Dmax for all sites. We also made seasonal measurements of the carbon isotope ratio of ecosystem respired CO2 (δR) in order to test for the expected correlation between shifts in environmental conditions and changes to the ecosystem-integrated ratio of leaf intercellular to ambient CO2 concentration (ci/ca). There was a consistent increase in δR values in the grassland, aspen forest and Douglas-fir forest associated with a seasonal reduction in soil moisture. Comparisons were made between WUE measured using eddy covariance with that calculated based on D and δR measurements. There was excellent agreement between WUE values calculated using the two techniques. Our δR measurements indicated that ci/ca values were quite similar among the Douglas-fir, aspen and grassland sites, despite large variation in environmental conditions among sites. This implied that the shorter-lived grass species had relatively high ci/ca values for the D of their habitat. By contrast, the longer-lived Douglas-fir trees were more conservative in water-use with lower ci/ca values relative to their habitat D. This illustrates the interaction between biological and environmental characteristics influencing ecosystem-level WUE. The strong correlation we observed between the two independent measurements of WUE, indicates that the stable isotope composition of respired CO2 is a useful ecosystem-scale tool to help study constraints to photosynthesis and acclimation of ecosystems to environmental stress.
The anisotropic and skewed turbulent motions on a broad scale range contribute to the complexity ... more The anisotropic and skewed turbulent motions on a broad scale range contribute to the complexity of dispersion patterns in the atmospheric convective boundary layer (CBL). The main turbulence forcing in the CBL is the convective heat transfer from a warm underlying surface. Several field, numerical and laboratory studies, see eg.
Carbon dioxide, water vapour, and energy fluxes vary spatially and temporally within forested env... more Carbon dioxide, water vapour, and energy fluxes vary spatially and temporally within forested environments. However, it is not clear to what extent they vary as a result of variability in the spatial distribution of biomass and elevation. The following study presents a new methodology for extracting changes in the structural characteristics of vegetation and elevation within footprint areas, for direct comparison with eddy covariance (EC) CO2 flux concentrations. The purpose was to determine whether within-site canopy structure and local elevation influenced CO2 fluxes in a mature jack pine (Pinus banksiana Lamb.) forest located in Saskatchewan, Canada. Airborne light detection and ranging (lidar) was used to extract tree height, canopy depth, foliage cover, and elevation within 30 min flux footprints. Within-footprint mean structural components and elevation were related to 30 min mean net ecosystem productivity (NEP) and gross ecosystem production (GEP). NEP and GEP were modeled u...
Background/Question/Methods: Eddy covariance (EC) observations of ecologically relevant trace gas... more Background/Question/Methods: Eddy covariance (EC) observations of ecologically relevant trace gas and energy fluxes are too sparse spatially for direct assimilation into gridded earth system models (ESMs) or for comparison with large-scale observations. The spatial coverage of a tower EC measurement may represent less than 1% of the domains typically covered by ESMs and remote sensing data. It is hence desirable to improve the spatial representativeness and temporal consistency of EC measurements for improving ecological inference. The objectives of this study are (i) to provide consistent flux time-series for target regions, rather than for a spatio-temporally variable patch of surface close to tower sites, and (ii) to test the applicability of the presented procedure across eco-climatological gradients covering some of the complexity of NEON sites. Based on the environmental response function approach (ERF, Metzger et al., 2013), we developed a procedure to produce spatio-temporal...
A newly developed pulsed cavity ring-down spectroscopy (CRDS) system for measuring atmospheric ga... more A newly developed pulsed cavity ring-down spectroscopy (CRDS) system for measuring atmospheric gaseous elemental mercury (GEM) concentrations at high temporal resolution (25 Hz) was used to successfully conduct the first eddy covariance (EC) flux measurements of GEM. GEM is the main gaseous atmospheric form, and quantification of bidirectional exchange between the Earth's surface and the atmosphere is important because gas exchange is important on a global scale. For example, surface GEM emissions from natural sources, legacy emissions, and re-emission of previously deposited anthropogenic pollution may exceed direct primary anthropogenic emissions. Using the EC technique for flux measurements requires subsecond measurements, which so far has not been feasible because of the slow time response of available instrumentation. The CRDS system measured GEM fluxes, which were compared to fluxes measured with the modified Bowen ratio (MBR) and a dynamic flux chamber (DFC). Measurements...
zip file contains documentation and a file in netcdf format with vegetation height distributions ... more zip file contains documentation and a file in netcdf format with vegetation height distributions between 0 and 70 m at 0.5 m intervals and at 0.5 by 0.5 degrees resolution. analysis is extended to 80 degrees N (previously to 60 degrees N).
Seven years of turbulent flux measurements from the Southern Old Aspen site in Saskatchewan, Cana... more Seven years of turbulent flux measurements from the Southern Old Aspen site in Saskatchewan, Canada, were analyzed to quantify the effect of systematic biases of data processing on half-hourly fluxes as well as annual estimates of net ecosystem production (NEP). Recently, efforts have intensified to unify the processing of half-hourly fluxes as well as annual carbon sequestration across flux tower
Soil water content can exert an important control on tree growth processes, an important consider... more Soil water content can exert an important control on tree growth processes, an important consideration for the boreal forest in Central Canada where climate change may bring about increased drought frequency. Empirical evidence has shown the strong coupling between conductance and photosynthesis, and the effect that drought can have on both variables. In models, canopy conductance and carbon uptake are
For the present study, we derived a footprint climatology for the Southern Old Aspen, Southern Ol... more For the present study, we derived a footprint climatology for the Southern Old Aspen, Southern Old Black Spruce, and Southern Old Jack Pine sites for the years 2005 to 2008. For each 30-min averaged sample period, the footprint area has been calculated taking into ...
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