ABSTRACT The BOREAS TF-4 team measured fluxes of CO2 and CH4 across the soil-air interface in fou... more ABSTRACT The BOREAS TF-4 team measured fluxes of CO2 and CH4 across the soil-air interface in four ages of jack pine forest at the BOREAS SSA during August 1993 to March 1995. Gross and net flux of CO2 and flux of CH4 between soil and air are presented for 24 chamber sites in mature jack pine forest, 20-year-old, 4-year-old, and clear cut areas. The data are stored in tabular ASCII files.
a g r i c u l t u r a l a n d f o r e s t m e t e o r o l o g y 1 4 8 ( 2 0 0 8 ) 5 9 2 -6 0 5 Hu... more a g r i c u l t u r a l a n d f o r e s t m e t e o r o l o g y 1 4 8 ( 2 0 0 8 ) 5 9 2 -6 0 5 Humidity Micrometeorology Soil moisture a b s t r a c t Stable isotopes provide insight into ecosystem carbon cycling, plant physiological processes, atmospheric boundary-layer dynamics, and are useful for the integration of processes over multiple scales. Of particular interest is the carbon isotope content (d 13 C) of nocturnal ecosystem-respired CO 2 (d R ). Recent advances in technology have made it possible to continuously examine the variation in d R within a forest canopy over relatively long timescales (months-years). We used tunable diode laser spectroscopy to examine d R at withinand below-canopy spatial locations in a Colorado subalpine forest (the Niwot Ridge Ameri-Flux site). We found a systematic pattern of increased d R within the forest canopy (d R-c ) compared to that near the ground (d R-g ). Values of d R-c were weakly correlated with the previous day's mean maximum daytime vapor pressure deficit (VPD). Conversely, there was a negative but still weak correlation between d R-g and time-lagged (0-5 days) daily mean soil moisture. The topography and presence of sustained nightly drainage flows at the Niwot Ridge forest site suggests that, on nights with stable atmospheric conditions, there is little mixing of air near the ground with that in the canopy. Atmospheric stability was assessed using thresholds of friction velocity, stability above the canopy, and bulk Richardson number within the canopy. When we selectively calculated d R-g and d R-c by removing time periods when ground and canopy air were well mixed, we found stronger correlations between d R-c and VPD, and d R-g and soil moisture. This suggests that there may be fundamental differences in the environmental controls on d R at sub-canopy spatial scales. These results may help explain the wide variance observed in the correlation of d R with different environmental parameters in other studies. (S.M. Schaeffer). a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / a g r f o r m e t
a g r i c u l t u r a l a n d f o r e s t m e t e o r o l o g y 1 4 8 ( 2 0 0 8 ) 5 9 2 -6 0 5 Hu... more a g r i c u l t u r a l a n d f o r e s t m e t e o r o l o g y 1 4 8 ( 2 0 0 8 ) 5 9 2 -6 0 5 Humidity Micrometeorology Soil moisture a b s t r a c t Stable isotopes provide insight into ecosystem carbon cycling, plant physiological processes, atmospheric boundary-layer dynamics, and are useful for the integration of processes over multiple scales. Of particular interest is the carbon isotope content (d 13 C) of nocturnal ecosystem-respired CO 2 (d R ). Recent advances in technology have made it possible to continuously examine the variation in d R within a forest canopy over relatively long timescales (months-years). We used tunable diode laser spectroscopy to examine d R at withinand below-canopy spatial locations in a Colorado subalpine forest (the Niwot Ridge Ameri-Flux site). We found a systematic pattern of increased d R within the forest canopy (d R-c ) compared to that near the ground (d R-g ). Values of d R-c were weakly correlated with the previous day's mean maximum daytime vapor pressure deficit (VPD). Conversely, there was a negative but still weak correlation between d R-g and time-lagged (0-5 days) daily mean soil moisture. The topography and presence of sustained nightly drainage flows at the Niwot Ridge forest site suggests that, on nights with stable atmospheric conditions, there is little mixing of air near the ground with that in the canopy. Atmospheric stability was assessed using thresholds of friction velocity, stability above the canopy, and bulk Richardson number within the canopy. When we selectively calculated d R-g and d R-c by removing time periods when ground and canopy air were well mixed, we found stronger correlations between d R-c and VPD, and d R-g and soil moisture. This suggests that there may be fundamental differences in the environmental controls on d R at sub-canopy spatial scales. These results may help explain the wide variance observed in the correlation of d R with different environmental parameters in other studies. (S.M. Schaeffer). a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / a g r f o r m e t
A prototype rapid-response CO2 sensor was used in conjunction with a Lyman-alpha hygrometer, fine... more A prototype rapid-response CO2 sensor was used in conjunction with a Lyman-alpha hygrometer, fine-wire thermocouples and a three-dimensional drag anemometer to measure CO2, humidity, temperature and wind velocity fluctuations. Measurements were made over a soybean crop grown on relatively flat terrain near Mead, Nebraska. Temperature, humidity and CO2 spectra measured under near neutral conditions were most similar in shape while longitudinal velocity ( U) spectra appeared to be somewhat broader. Peaks occurred around f = 0.02 to 0.06 (where f is the non-dimensional frequency) in all spectra except for vertical velocity which had a peak near f = 0.5. As thermal stability changed from neutral to stable, spectra exhibited lower peaks, were narrower in shape and were shifted towards higher frequencies. Opposite behavior was observed with increasing instability. Cospectra for momentum, heat, water vapor and CO2 measured during neutral conditions had similar peak frequencies (near f = 0.15). Among the cospectra studied, CO2 and water vapor cospectra had the greatest similarity in shape.
The BOREAS TF-4 team measured fluxes of CO2 and CH4 across the soil-air interface in four ages of... more The BOREAS TF-4 team measured fluxes of CO2 and CH4 across the soil-air interface in four ages of jack pine forest at the BOREAS SSA during August 1993 to March 1995. Gross and net flux of CO2 and flux of CH4 between soil and air are presented for 24 chamber sites in mature jack pine forest, 20-year-old, 4-year-old, and clear cut areas. The data are stored in tabular ASCII files.
Urban ecosystems are currently characterized by rapid growth, are expected to continually expand ... more Urban ecosystems are currently characterized by rapid growth, are expected to continually expand and, thus, represent an important driver of land use change. A significant component of urban ecosystems is lawns, potentially the single largest irrigated "crop" in the U.S. Beginning in March of 2011 (ahead of the growing season), eddy covariance measurements of net carbon exchange and evapotranspiration along with energy balance fluxes were conducted for a well-watered, fertilized lawn (rye-bluegrass-mix) in metropolitan Denver and for a nearby tallgrass prairie (big bluestem, switchgrass, cheatgrass, blue grama). Due to the semi-arid climate conditions of the Denver region, differences in management (i.e., irrigation and fertilization) are expected to have a discernible impact on ecosystem productivity and thus on carbon sequestration rates, evapotranspiration, and the sensible and latent heat partitioning of the energy balance. By mid-July, preliminary data indicated that ...
Near surface soil-water content is crucial to the sustainability of an ecosystem. Additionally, t... more Near surface soil-water content is crucial to the sustainability of an ecosystem. Additionally, the feedbacks between soil water and soil carbon improve the ability to predict carbon sequestration rates. Organic-carbon content in surface soils influences soil texture and, subsequently, water holding capacity. Preliminary research for two growing seasons (2010 and 2011) compares soil water, temperature, heat flux, and evapotranspiration (ET) with soil organic carbon content at several sites in the Colorado Front Range. Continuous measurements of precipitation, soil moisture and temperature, and energy fluxes were conducted from eddy covariance flux towers at three sites around metropolitan Denver: one urban site and two adjacent sites, a montane forest (Flying J Ranch Open Space), and a native tallgrass prairie (Rocky Flats National Wildlife Refuge (NWR)). Irrigation data were obtained for the Denver urban site and added to its precipitation to obtain total water inputs. Soil samples...
Although urban areas occupy just a few percent of US land area, they are expanding rapidly and ar... more Although urban areas occupy just a few percent of US land area, they are expanding rapidly and are expected to maintain this trend for the foreseeable future. Within these domains is the largest irrigated crop in the US - lawns. Utilizing eddy covariance instruments, surface chambers, and destructive leaf sampling, well watered, fertilized lawns in metropolitan Denver were found to sequester substantially more carbon (1.3 T C ha-1 yr-1) than adjacent native grassland (0.6 T C ha-1 yr-1) over a growing season. Due to the semi-arid environment, contrasts in lawn management (irrigation and fertilization) led to wide variation in carbon sequestration rates, evapotranspiration, and the sensible and latent heat partitioning of the energy balance. Measured leaf area was correlated with remotely sensed vegetation indices obtained from aircraft and satellite hyperspectral instruments to quantify spatial variability in leaf area over contrasting land surfaces and lawn management practices. Th...
Data are provided from 17 single-swath aerial spray trials that were conducted over a fully leafe... more Data are provided from 17 single-swath aerial spray trials that were conducted over a fully leafed, 16-m tall, mixed oak forest. The distribution of cross-swath spray deposits was sampled at the top of the canopy and below the canopy. Micrometeorological conditions were measured above and within the canopy during the spray trials. The USDA Forest Service FSCBG (Forest Service-Cramer-Barry-Grim) model was run to predict the target sampler catch for each trial using forest stand, airplane-application-equipment configuration, and micrometeorological conditions as inputs. Observations showed an average cross-swath deposition of 100 IU cm2 with large run-to-run variability in deposition patterns, magnitudes, and drift. Eleven percent of the spray material that reached the top of the canopy penetrated through the tree canopy to the forest floor.The FSCBG predictions of the ensemble-averaged deposition were within 17% of the measured deposition at the canopy top and within 8% on the ground...
ABSTRACT The BOREAS TF-4 team measured fluxes of CO2 and CH4 across the soil-air interface in fou... more ABSTRACT The BOREAS TF-4 team measured fluxes of CO2 and CH4 across the soil-air interface in four ages of jack pine forest at the BOREAS SSA during August 1993 to March 1995. Gross and net flux of CO2 and flux of CH4 between soil and air are presented for 24 chamber sites in mature jack pine forest, 20-year-old, 4-year-old, and clear cut areas. The data are stored in tabular ASCII files.
a g r i c u l t u r a l a n d f o r e s t m e t e o r o l o g y 1 4 8 ( 2 0 0 8 ) 5 9 2 -6 0 5 Hu... more a g r i c u l t u r a l a n d f o r e s t m e t e o r o l o g y 1 4 8 ( 2 0 0 8 ) 5 9 2 -6 0 5 Humidity Micrometeorology Soil moisture a b s t r a c t Stable isotopes provide insight into ecosystem carbon cycling, plant physiological processes, atmospheric boundary-layer dynamics, and are useful for the integration of processes over multiple scales. Of particular interest is the carbon isotope content (d 13 C) of nocturnal ecosystem-respired CO 2 (d R ). Recent advances in technology have made it possible to continuously examine the variation in d R within a forest canopy over relatively long timescales (months-years). We used tunable diode laser spectroscopy to examine d R at withinand below-canopy spatial locations in a Colorado subalpine forest (the Niwot Ridge Ameri-Flux site). We found a systematic pattern of increased d R within the forest canopy (d R-c ) compared to that near the ground (d R-g ). Values of d R-c were weakly correlated with the previous day's mean maximum daytime vapor pressure deficit (VPD). Conversely, there was a negative but still weak correlation between d R-g and time-lagged (0-5 days) daily mean soil moisture. The topography and presence of sustained nightly drainage flows at the Niwot Ridge forest site suggests that, on nights with stable atmospheric conditions, there is little mixing of air near the ground with that in the canopy. Atmospheric stability was assessed using thresholds of friction velocity, stability above the canopy, and bulk Richardson number within the canopy. When we selectively calculated d R-g and d R-c by removing time periods when ground and canopy air were well mixed, we found stronger correlations between d R-c and VPD, and d R-g and soil moisture. This suggests that there may be fundamental differences in the environmental controls on d R at sub-canopy spatial scales. These results may help explain the wide variance observed in the correlation of d R with different environmental parameters in other studies. (S.M. Schaeffer). a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / a g r f o r m e t
a g r i c u l t u r a l a n d f o r e s t m e t e o r o l o g y 1 4 8 ( 2 0 0 8 ) 5 9 2 -6 0 5 Hu... more a g r i c u l t u r a l a n d f o r e s t m e t e o r o l o g y 1 4 8 ( 2 0 0 8 ) 5 9 2 -6 0 5 Humidity Micrometeorology Soil moisture a b s t r a c t Stable isotopes provide insight into ecosystem carbon cycling, plant physiological processes, atmospheric boundary-layer dynamics, and are useful for the integration of processes over multiple scales. Of particular interest is the carbon isotope content (d 13 C) of nocturnal ecosystem-respired CO 2 (d R ). Recent advances in technology have made it possible to continuously examine the variation in d R within a forest canopy over relatively long timescales (months-years). We used tunable diode laser spectroscopy to examine d R at withinand below-canopy spatial locations in a Colorado subalpine forest (the Niwot Ridge Ameri-Flux site). We found a systematic pattern of increased d R within the forest canopy (d R-c ) compared to that near the ground (d R-g ). Values of d R-c were weakly correlated with the previous day's mean maximum daytime vapor pressure deficit (VPD). Conversely, there was a negative but still weak correlation between d R-g and time-lagged (0-5 days) daily mean soil moisture. The topography and presence of sustained nightly drainage flows at the Niwot Ridge forest site suggests that, on nights with stable atmospheric conditions, there is little mixing of air near the ground with that in the canopy. Atmospheric stability was assessed using thresholds of friction velocity, stability above the canopy, and bulk Richardson number within the canopy. When we selectively calculated d R-g and d R-c by removing time periods when ground and canopy air were well mixed, we found stronger correlations between d R-c and VPD, and d R-g and soil moisture. This suggests that there may be fundamental differences in the environmental controls on d R at sub-canopy spatial scales. These results may help explain the wide variance observed in the correlation of d R with different environmental parameters in other studies. (S.M. Schaeffer). a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / a g r f o r m e t
A prototype rapid-response CO2 sensor was used in conjunction with a Lyman-alpha hygrometer, fine... more A prototype rapid-response CO2 sensor was used in conjunction with a Lyman-alpha hygrometer, fine-wire thermocouples and a three-dimensional drag anemometer to measure CO2, humidity, temperature and wind velocity fluctuations. Measurements were made over a soybean crop grown on relatively flat terrain near Mead, Nebraska. Temperature, humidity and CO2 spectra measured under near neutral conditions were most similar in shape while longitudinal velocity ( U) spectra appeared to be somewhat broader. Peaks occurred around f = 0.02 to 0.06 (where f is the non-dimensional frequency) in all spectra except for vertical velocity which had a peak near f = 0.5. As thermal stability changed from neutral to stable, spectra exhibited lower peaks, were narrower in shape and were shifted towards higher frequencies. Opposite behavior was observed with increasing instability. Cospectra for momentum, heat, water vapor and CO2 measured during neutral conditions had similar peak frequencies (near f = 0.15). Among the cospectra studied, CO2 and water vapor cospectra had the greatest similarity in shape.
The BOREAS TF-4 team measured fluxes of CO2 and CH4 across the soil-air interface in four ages of... more The BOREAS TF-4 team measured fluxes of CO2 and CH4 across the soil-air interface in four ages of jack pine forest at the BOREAS SSA during August 1993 to March 1995. Gross and net flux of CO2 and flux of CH4 between soil and air are presented for 24 chamber sites in mature jack pine forest, 20-year-old, 4-year-old, and clear cut areas. The data are stored in tabular ASCII files.
Urban ecosystems are currently characterized by rapid growth, are expected to continually expand ... more Urban ecosystems are currently characterized by rapid growth, are expected to continually expand and, thus, represent an important driver of land use change. A significant component of urban ecosystems is lawns, potentially the single largest irrigated "crop" in the U.S. Beginning in March of 2011 (ahead of the growing season), eddy covariance measurements of net carbon exchange and evapotranspiration along with energy balance fluxes were conducted for a well-watered, fertilized lawn (rye-bluegrass-mix) in metropolitan Denver and for a nearby tallgrass prairie (big bluestem, switchgrass, cheatgrass, blue grama). Due to the semi-arid climate conditions of the Denver region, differences in management (i.e., irrigation and fertilization) are expected to have a discernible impact on ecosystem productivity and thus on carbon sequestration rates, evapotranspiration, and the sensible and latent heat partitioning of the energy balance. By mid-July, preliminary data indicated that ...
Near surface soil-water content is crucial to the sustainability of an ecosystem. Additionally, t... more Near surface soil-water content is crucial to the sustainability of an ecosystem. Additionally, the feedbacks between soil water and soil carbon improve the ability to predict carbon sequestration rates. Organic-carbon content in surface soils influences soil texture and, subsequently, water holding capacity. Preliminary research for two growing seasons (2010 and 2011) compares soil water, temperature, heat flux, and evapotranspiration (ET) with soil organic carbon content at several sites in the Colorado Front Range. Continuous measurements of precipitation, soil moisture and temperature, and energy fluxes were conducted from eddy covariance flux towers at three sites around metropolitan Denver: one urban site and two adjacent sites, a montane forest (Flying J Ranch Open Space), and a native tallgrass prairie (Rocky Flats National Wildlife Refuge (NWR)). Irrigation data were obtained for the Denver urban site and added to its precipitation to obtain total water inputs. Soil samples...
Although urban areas occupy just a few percent of US land area, they are expanding rapidly and ar... more Although urban areas occupy just a few percent of US land area, they are expanding rapidly and are expected to maintain this trend for the foreseeable future. Within these domains is the largest irrigated crop in the US - lawns. Utilizing eddy covariance instruments, surface chambers, and destructive leaf sampling, well watered, fertilized lawns in metropolitan Denver were found to sequester substantially more carbon (1.3 T C ha-1 yr-1) than adjacent native grassland (0.6 T C ha-1 yr-1) over a growing season. Due to the semi-arid environment, contrasts in lawn management (irrigation and fertilization) led to wide variation in carbon sequestration rates, evapotranspiration, and the sensible and latent heat partitioning of the energy balance. Measured leaf area was correlated with remotely sensed vegetation indices obtained from aircraft and satellite hyperspectral instruments to quantify spatial variability in leaf area over contrasting land surfaces and lawn management practices. Th...
Data are provided from 17 single-swath aerial spray trials that were conducted over a fully leafe... more Data are provided from 17 single-swath aerial spray trials that were conducted over a fully leafed, 16-m tall, mixed oak forest. The distribution of cross-swath spray deposits was sampled at the top of the canopy and below the canopy. Micrometeorological conditions were measured above and within the canopy during the spray trials. The USDA Forest Service FSCBG (Forest Service-Cramer-Barry-Grim) model was run to predict the target sampler catch for each trial using forest stand, airplane-application-equipment configuration, and micrometeorological conditions as inputs. Observations showed an average cross-swath deposition of 100 IU cm2 with large run-to-run variability in deposition patterns, magnitudes, and drift. Eleven percent of the spray material that reached the top of the canopy penetrated through the tree canopy to the forest floor.The FSCBG predictions of the ensemble-averaged deposition were within 17% of the measured deposition at the canopy top and within 8% on the ground...
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