scholarly journals Comparison between eddy covariance and automatic chamber techniques for measuring net ecosystem exchange of carbon dioxide in cotton and wheat fields

2013 ◽  
Vol 10 (11) ◽  
pp. 6865-6877 ◽  
Author(s):  
K. Wang ◽  
C. Liu ◽  
X. Zheng ◽  
M. Pihlatie ◽  
B. Li ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Eddy Covariance ◽  
Net Ecosystem Exchange ◽  
Cotton Field ◽  
Wheat Field ◽  
Cropping Season ◽  
Flux Measurements ◽  
One Year ◽  
Carbon Dioxide Co2 ◽  
B Test

Abstract. Static and transparent automatic chamber (AC) technique is a necessary choice for measuring net ecosystem exchange (NEE) of carbon dioxide (CO2) in circumstances where eddy covariance (EC) technique is not applicable. However, a comparison of the two techniques for measurements on croplands has seldom been undertaken. We carried out NEE observations in a cotton field (for one year) and a winter wheat field (for one cropping season) using both AC and EC techniques, to (a) compare the NEE fluxes measured using each technique, and (b) test the NEE measurement performance of an automatic chamber system (AMEG), which was designed for simultaneous flux measurements of multiple gases. The half-hourly NEE fluxes measured with the two techniques were in approximate agreement, with the AC fluxes being 0.78 (cotton) and 1.06 (wheat) times the size of the EC fluxes. When integrated to daily timescale, the fluxes of the two techniques were in better agreement, showing an average ratio of 0.94 and 1.00 for the cotton and wheat, respectively. During the periods with comparable field conditions and normal performance of both instruments, the cumulative NEE fluxes revealed small differences between the two techniques (−9.0% ~ 7%, with a mean of 0.1%). The measurements resulted in an annual cumulative NEE of −40 g C m−2 yr−1 (EC) and −42 g C m−2 yr−1 (AC) in the cotton field, and a seasonal cumulative NEE of −251 g C m−2 (EC) and −205 g C m−2 (AC) in the wheat field. Our results indicate that, for cropland populated by short plants, the AMEG system and the data processing procedures applied in this study are able to provide NEE estimates comparable to those from EC measurements.

scholarly journals Comparison between eddy covariance and automatic chamber techniques for measuring net ecosystem exchange of carbon dioxide in cotton and wheat fields

2013 ◽  
Vol 10 (5) ◽  
pp. 8467-8503 ◽  
Author(s):  
K. Wang ◽  
C. Liu ◽  
X. Zheng ◽  
M. Pihlatie ◽  
B. Li ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Eddy Covariance ◽  
Calcareous Soils ◽  
Net Ecosystem Exchange ◽  
Cotton Field ◽  
Wheat Field ◽  
Cropping Season ◽  
Flux Measurements ◽  
One Year ◽  
Carbon Dioxide Co2

Abstract. Static and transparent automatic chamber (AC) technique is a~necessary choice for measuring net ecosystem exchange (NEE) of carbon dioxide (CO2) in circumstances where eddy covariance (EC) technique is not applicable. However, a comparison of the two techniques for measurements on croplands has seldom been undertaken. We carried out NEE observations in a cotton field (for one year) and a winter wheat field (for one cropping season) using both AC and EC techniques, to (a) compare the NEE fluxes measured using each technique, and (b) test the NEE measurement performance of an automatic chamber system (AMEG), which was designed for simultaneous flux measurements of multiple gases. The half-hourly NEE fluxes measured with the two techniques were in approximate agreement, with the AC fluxes being 0.78 (cotton) and 1.06 (wheat) times those of the EC. When integrated to daily timescale, the fluxes of the two techniques were in better agreement, showing an average ratio of 0.94 and 1.00 for the cotton and wheat, respectively. During the periods with comparable field conditions and normal performance of both instruments, the cumulative NEE fluxes revealed small differences between the two techniques (–9.0 ~ 6.7%, with a mean of 0.1%). The measurements resulted in annual cumulative NEE of –40 g C m–2 yr–1 (EC) and –42 g C m–2 yr–1 (AC) in the cotton field and seasonal cumulative NEE of –251 g C m–2 (EC) and –205 g C m–2 (AC) in the wheat field. Our results indicate that, for cropland populated by short plants, the AMEG system and the data processing procedures applied in this study are able to provide NEE estimates comparable to those from EC measurements, although either technique may lead to an overestimation of the loss rate (or underestimation of the gain rate) of the soil organic carbon stock of an ecosystem, in particular with calcareous soils exposed to increasing atmospheric acid deposition.

Eddy covariance flux measurements of momentum, heat and carbon dioxide in Hudson Bay at the onset of sea ice melt 

2021 ◽  
Author(s):  
Richard Sims ◽  
Brian Butterworth ◽  
Tim Papakyriakou ◽  
Mohamed Ahmed ◽  
Brent Else
Keyword(s):  
Carbon Dioxide ◽  
Gas Exchange ◽  
Sea Ice ◽  
Eddy Covariance ◽  
Open Water ◽  
The Arctic ◽  
Gas Transfer ◽  
Hudson Bay ◽  
Flux Measurements ◽  
Ice Fraction

<p>Remoteness and tough conditions have made the Arctic Ocean historically difficult to access; until recently this has resulted in an undersampling of trace gas and gas exchange measurements. The seasonal cycle of sea ice completely transforms the air sea interface and the dynamics of gas exchange. To make estimates of gas exchange in the presence of sea ice, sea ice fraction is frequently used to scale open water gas transfer parametrisations. It remains unclear whether this scaling is appropriate for all sea ice regions. Ship based eddy covariance measurements were made in Hudson Bay during the summer of 2018 from the icebreaker CCGS Amundsen. We will present fluxes of carbon dioxide (CO<sub>2</sub>), heat and momentum and will show how they change around the Hudson Bay polynya under varying sea ice conditions. We will explore how these fluxes change with wind speed and sea ice fraction. As freshwater stratification was encountered during the cruise, we will compare our measurements with other recent eddy covariance flux measurements made from icebreakers and also will compare our turbulent CO<sub>2 </sub>fluxes with bulk fluxes calculated using underway and surface bottle pCO<sub>2</sub> data. </p><p> </p>

scholarly journals Greenhouse gas flux measurements in a forestry-drained peatland indicate a large carbon sink

2011 ◽  
Vol 8 (11) ◽  
pp. 3203-3218 ◽  
Author(s):  
A. Lohila ◽  
K. Minkkinen ◽  
M. Aurela ◽  
J.-P. Tuovinen ◽  
T. Penttilä ◽  
...  
Keyword(s):  
Carbon Sink ◽  
Accumulation Rate ◽  
Peat Soil ◽  
Net Ecosystem Exchange ◽  
Flux Measurement ◽  
Co2 Exchange ◽  
Co2 Uptake ◽  
Flux Measurements ◽  
Ch4 And N2o ◽  
Carbon Dioxide Co2

Abstract. Drainage for forestry purposes increases the depth of the oxic peat layer and leads to increased growth of shrubs and trees. Concurrently, the production and uptake of the greenhouse gases carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) change: due to the accelerated decomposition of peat in the presence of oxygen, drained peatlands are generally considered to lose peat carbon (C). We measured CO2 exchange with the eddy covariance (EC) method above a drained nutrient-poor peatland forest in southern Finland for 16 months in 2004–2005. The site, classified as a dwarf-shrub pine bog, had been ditched about 35 years earlier. CH4 and N2O fluxes were measured at 2–5-week intervals with the chamber technique. Drainage had resulted in a relatively little change in the water table level, being on average 40 cm below the ground in 2005. The annual net ecosystem exchange was −870 ± 100 g CO2 m−2 yr−1 in the calendar year 2005, indicating net CO2 uptake from the atmosphere. The site was a small sink of CH4 (−0.12 g CH4 m−2 yr−1) and a small source of N2O (0.10 g N2O m−2 yr−1). Photosynthesis was detected throughout the year when the air temperature exceeded −3 °C. As the annual accumulation of C in the above and below ground tree biomass (175 ± 35 g C m−2) was significantly lower than the accumulation observed by the flux measurement (240 ± 30 g C m−2), about 65 g C m−2 yr−1 was likely to have accumulated as organic matter into the peat soil. This is a higher average accumulation rate than previously reported for natural northern peatlands, and the first time C accumulation has been shown by EC measurements to occur in a forestry-drained peatland. Our results suggest that forestry-drainage may significantly increase the CO2 uptake rate of nutrient-poor peatland ecosystems.

scholarly journals Dried, closed-path eddy covariance method for measuring carbon dioxide flux over sea ice

2018 ◽  
Vol 11 (11) ◽  
pp. 6075-6090 ◽  
Author(s):  
Brian J. Butterworth ◽  
Brent G. T. Else
Keyword(s):  
Carbon Dioxide ◽  
Sea Ice ◽  
Eddy Covariance ◽  
Co2 Flux ◽  
Carbon Dioxide Flux ◽  
The Arctic ◽  
Closed Path ◽  
Eddy Covariance Method ◽  
Open Path ◽  
Flux Measurements

Abstract. The Arctic marine environment plays an important role in the global carbon cycle. However, there remain large uncertainties in how sea ice affects air–sea fluxes of carbon dioxide (CO2), partially due to disagreement between the two main methods (enclosure and eddy covariance) for measuring CO2 flux (FCO2). The enclosure method has appeared to produce more credible FCO2 than eddy covariance (EC), but is not suited for collecting long-term, ecosystem-scale flux datasets in such remote regions. Here we describe the design and performance of an EC system to measure FCO2 over landfast sea ice that addresses the shortcomings of previous EC systems. The system was installed on a 10 m tower on Qikirtaarjuk Island – a small rock outcrop in Dease Strait located roughly 35 km west of Cambridge Bay, Nunavut, in the Canadian Arctic Archipelago. The system incorporates recent developments in the field of air–sea gas exchange by measuring atmospheric CO2 using a closed-path infrared gas analyzer (IRGA) with a dried sample airstream, thus avoiding the known water vapor issues associated with using open-path IRGAs in low-flux environments. A description of the methods and the results from 4 months of continuous flux measurements from May through August 2017 are presented, highlighting the winter to summer transition from ice cover to open water. We show that the dried, closed-path EC system greatly reduces the magnitude of measured FCO2 compared to simultaneous open-path EC measurements, and for the first time reconciles EC and enclosure flux measurements over sea ice. This novel EC installation is capable of operating year-round on solar and wind power, and therefore promises to deliver new insights into the magnitude of CO2 fluxes and their driving processes through the annual sea ice cycle.

scholarly journals Ecosystem fluxes of hydrogen: a comparison of flux-gradient methods

2014 ◽  
Vol 7 (9) ◽  
pp. 2787-2805 ◽  
Author(s):  
L. K. Meredith ◽  
R. Commane ◽  
J. W. Munger ◽  
A. Dunn ◽  
J. Tang ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Forest Canopy ◽  
Trace Gases ◽  
Gradient Methods ◽  
Net Ecosystem Exchange ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Flux Gradient ◽  
Harvard Forest ◽  
Flux Measurements

Abstract. Our understanding of biosphere–atmosphere exchange has been considerably enhanced by eddy covariance measurements. However, there remain many trace gases, such as molecular hydrogen (H2), that lack suitable analytical methods to measure their fluxes by eddy covariance. In such cases, flux-gradient methods can be used to calculate ecosystem-scale fluxes from vertical concentration gradients. The budget of atmospheric H2 is poorly constrained by the limited available observations, and thus the ability to quantify and characterize the sources and sinks of H2 by flux-gradient methods in various ecosystems is important. We developed an approach to make nonintrusive, automated measurements of ecosystem-scale H2 fluxes both above and below the forest canopy at the Harvard Forest in Petersham, Massachusetts, for over a year. We used three flux-gradient methods to calculate the fluxes: two similarity methods that do not rely on a micrometeorological determination of the eddy diffusivity, K, based on (1) trace gases or (2) sensible heat, and one flux-gradient method that (3) parameterizes K. We quantitatively assessed the flux-gradient methods using CO2 and H2O by comparison to their simultaneous independent flux measurements via eddy covariance and soil chambers. All three flux-gradient methods performed well in certain locations, seasons, and times of day, and the best methods were trace gas similarity for above the canopy and K parameterization below it. Sensible heat similarity required several independent measurements, and the results were more variable, in part because those data were only available in the winter, when heat fluxes and temperature gradients were small and difficult to measure. Biases were often observed between flux-gradient methods and the independent flux measurements, and there was at least a 26% difference in nocturnal eddy-derived net ecosystem exchange (NEE) and chamber measurements. H2 fluxes calculated in a summer period agreed within their uncertainty and pointed to soil uptake as the main driver of H2 exchange at Harvard Forest, with H2 deposition velocities ranging from 0.04 to 0.10 cm s−1.

scholarly journals Carbon exchange between the atmosphere and subtropical forested cypress and pine wetlands

2014 ◽  
Vol 11 (11) ◽  
pp. 15753-15791
Author(s):  
W. B. Shoemaker ◽  
J. G. Barr ◽  
D. B. Botkin ◽  
S. L. Graham
Keyword(s):  
Carbon Dioxide ◽  
Methane Emission ◽  
Vegetation Index ◽  
Overland Flow ◽  
Net Ecosystem Exchange ◽  
Forested Wetland ◽  
Carbon Dioxide Exchange ◽  
Cypress Swamp ◽  
Ch4 Production ◽  
Carbon Dioxide Co2

Abstract. Carbon dioxide exchange between the atmosphere and forested subtropical wetlands is largely unknown. Here we report a first step in characterizing this atmospheric–ecosystem carbon (C) exchange, for cypress strands and pine forests in the Greater Everglades of Florida as measured with eddy covariance methods at three locations (Cypress Swamp, Dwarf Cypress and Pine Upland) for one year. Links between water and C cycles are examined at these three sites, and methane emission measured only at the Dwarf Cypress site. Each forested wetland showed net C uptake (retained in the soil and biomass or transported laterally via overland flow) from the atmosphere monthly and annually. Net ecosystem exchange (NEE) of carbon dioxide (CO2) (difference between photosynthesis and respiration, with negative values representing net ecosystem uptake) was greatest at the Cypress Swamp (−1000 g C m-2 year-1), moderate at the Pine Upland (−900 g C m-2 year-1), and least at the Dwarf Cypress (−500 g C m-2 year-1). Methane emission was a negligible part of the C (12 g C m-2 year-1) budget when compared to NEE. However, methane (CH4) production was considerable in terms of global warming potential, as about 20 g CH4 emitted per m2 year was equivalent to about 500 g CO2 emitted per m2 year}. Changes in NEE were clearly a function of seasonality in solar insolation, air temperature and water availability from rainfall. We also note that changes in the satellite-derived enhanced-vegetation index (EVI) served as a useful surrogate for changes in net and gross atmospheric–ecosystem C exchange at these forested wetland sites.

scholarly journals Comparison of floating chamber and eddy covariance measurements of lake greenhouse gas fluxes

2013 ◽  
Vol 10 (11) ◽  
pp. 18309-18335 ◽  
Author(s):  
E. Podgrajsek ◽  
E. Sahlée ◽  
D. Bastviken ◽  
J. Holst ◽  
A. Lindroth ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Carbon Sink ◽  
Co2 Flux ◽  
Flux Footprint ◽  
Gas Fluxes ◽  
Partial Pressure Of Co2 ◽  
Flux Measurements ◽  
Eddy Covariance Measurements ◽  
Terrestrial Carbon Sink ◽  
Carbon Dioxide Co2

Abstract. Fluxes of carbon dioxide (CO2) and methane (CH4) from lakes may have a large impact on the magnitude of the terrestrial carbon sink. Traditionally lake fluxes have been measured using the floating chambers (FC) technique, however, several recent studies use the eddy covariance (EC) method. We present simultaneous flux measurements using both methods at the lake Tämnaren in Sweden during field campaigns in 2011 and 2012. Only very few similar studies exist. For CO2 flux, the two methods agree relatively well during some periods, but deviate substantially at other times. The large discrepancies might be caused by heterogeneity of partial pressure of CO2 (pCO2w) in the EC flux footprint. The methods agree better for CH4 fluxes, it is, however, clear that short-term discontinuous FC measurements are likely to miss important high flux events.

scholarly journals First eddy covariance flux measurements of gaseous elemental mercury (Hg<sup>0</sup>) over a grassland

2019 ◽  
Author(s):  
Stefan Osterwalder ◽  
Werner Eugster ◽  
Iris Feigenwinter ◽  
Martin Jiskra
Keyword(s):  
Detection Limit ◽  
Eddy Covariance ◽  
Net Ecosystem Exchange ◽  
Elemental Mercury ◽  
Terrestrial Ecosystems ◽  
Co2 Uptake ◽  
Gaseous Elemental Mercury ◽  
Flux Measurements ◽  
Net Co2 Uptake

Abstract. Direct measurements of the net ecosystem exchange (NEE) of gaseous elemental mercury (Hg0) are crucial to improve the understanding of global Hg cycling und ultimately human and wildlife Hg exposure. The lack of long-term, ecosystem-scale measurements causes large uncertainties in Hg0 flux estimates. Today it remains unclear whether terrestrial ecosystems are net sinks or sources of atmospheric Hg0. Here we show a detailed validation of the eddy covariance technique for direct Hg0 flux measurements (Eddy Mercury) based on a Lumex mercury monitor RA-915AM. The flux detection limit derived from a zero-flux experiment in the laboratory was 0.22 ng m−2 h−1 (maximum) with a 50 % cut-off at 0.074 ng m−2 h−1. The statistical estimate of the Hg0 flux detection limit under real-world outdoor conditions at the site was 5.9 ng m−2 h−1 (50 % cut-off). We present the first successful eddy covariance NEE measurements of Hg0 over a low-Hg level soil (41–75 ng Hg g−1 topsoil [0–10 cm]) in summer 2018 at a managed grassland at the Swiss FluxNet site in Chamau, Switzerland (CH-Cha). We measured a net summertime re-emission over a period of 34 days with a median Hg0 flux of 2.5 ng m−2 h−1 (−0.6 to 7.4 ng m−2 h−1, range between 25th and 75th percentiles). We observed a distinct diel cycle with higher median daytime fluxes (8.4 ng m−2 h−1) than nighttime fluxes (1.0 ng m−2 h−1). Drought stress during the measurement campaign in summer 2018 induced partial stomata closure of vegetation which led to a midday depression in CO2 uptake which did not recover during the afternoon. Thus, the cumulative net CO2 uptake was only 8 % of the net CO2 uptake during the same period in the previous year 2017. We suggest that partial stomata closure dampened Hg0 uptake by vegetation, resulting in a NEE of Hg0 dominated by soil re-emission. Finally, we give suggestions to further improve the precision and handling of the Eddy Mercury system in order to assure its suitability for long-term NEE measurements of Hg0 over natural background surfaces with low soil Hg concentrations (

scholarly journals Ecosystem fluxes of hydrogen: a comparison of flux-gradient methods

2014 ◽  
Vol 7 (3) ◽  
pp. 2879-2928 ◽  
Author(s):  
L. K. Meredith ◽  
R. Commane ◽  
J. W. Munger ◽  
A. Dunn ◽  
J. Tang ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Forest Canopy ◽  
Trace Gases ◽  
Gradient Methods ◽  
Net Ecosystem Exchange ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Flux Gradient ◽  
Harvard Forest ◽  
Flux Measurements

Abstract. Our understanding of biosphere-atmosphere exchange has been considerably enhanced by eddy-covariance measurements, however there remain many trace gases, such as molecular hydrogen (H2), for which there are no suitable analytical methods to measure their fluxes by eddy covariance. In such cases, flux-gradient methods can be used to calculate ecosystem-scale fluxes from vertical concentration gradients. The budget of atmospheric H2 is poorly constrained by the limited available observations, thus the ability to quantify and characterize the sources and sinks of H2 by flux-gradient methods in various ecosystems is important. We developed an approach to make nonintrusive, automated measurements of ecosystem-scale H2 fluxes both above and below the forest canopy at the Harvard Forest in Petersham, MA for over a year. We used three flux-gradient methods to calculate the fluxes: two similarity methods that do not rely on a micrometeorological determination of the eddy diffusivity, K, based on (1) trace gases or (2) sensible heat and one flux-gradient method that (3) parameterizes K. We quantitatively assessed the flux-gradient methods on CO2 and H2O by comparison to their simultaneous independent flux measurements via eddy covariance and chambers. All three flux-gradient methods performed well in certain locations, seasons, and times of day, and the best methods were trace gas similarity above and K parameterization below the canopy. Sensible heat similarity required several independent measurements and the results were more variable, in part because those data were only available in the winter when heat fluxes and temperature gradients were small and difficult to measure. Biases were often observed between flux-gradient methods and the independent flux measurements, including at least a 26% difference in nocturnal eddy-derived Net Ecosystem Exchange (NEE) and soil chamber measurements. All flux-gradient methods used to calculate above and below canopy H2 fluxes pointed to soil uptake as the main driver of H2 exchange at Harvard Forest. H2 fluxes calculated in a summer period agreed within their uncertainty and indicated that H2 deposition velocities ranged from 0.04 to 0.1 cm s−1.

First application of low-cost eddy covariance for CO2 fluxes over agroforestry

2020 ◽  
Author(s):  
Justus van Ramshorst ◽  
Christian Markwitz ◽  
Timothy Hill ◽  
Robert Clement ◽  
Alexander Knohl ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Low Cost ◽  
Net Ecosystem Exchange ◽  
Agroforestry Systems ◽  
Agricultural System ◽  
Data Series ◽  
Custom Made ◽  
Flux Measurements ◽  
Eddy Covariance System ◽  
The Difference

&lt;p&gt;Agroforestry is a combination of monoculture agriculture and trees. Studies of net ecosystem exchange of CO&lt;sub&gt;2&lt;/sub&gt; (NEE) of agroforestry systems are rare, in comparison to the extensive studies of NEE of agricultural systems (croplands and grasslands). Agroforestry has been shown to alter the microclimate, productivity, and nutrient and water usage &amp;#8211; as compared to standard agricultural practise. The, potentially, higher carbon sequestration of agroforestry, relative to monoculture systems, provides an interesting option for mitigating climate change, highlighting the need for improved study of agroforestry systems. The current study, as part of the SIGNAL (sustainable intensification of agriculture through agroforestry) project, investigates NEE of agroforestry compared to that of monoculture agriculture. The study employs paired comparisons of flux measurements above agroforestry and monoculture agronomy, replicated at five locations across Germany. Fluxes are measured, using innovative low-cost CO&lt;sub&gt;2&lt;/sub&gt; eddy covariance sensors (slow response Vaisala GMP343 IRGA with custom made housing), which have been successfully used in a study over grassland. Continuous data series from mid-summer until winter 2019 show that both systems acted as a sink with comparable fluxes during summer. The diurnal CO&lt;sub&gt;2&lt;/sub&gt; cycle and the response to management activities are distinguishable and in autumn preliminary results suggest a small difference in fluxes between the two systems. The low-cost eddy covariance system is able to capture the turbulence and to measure the CO&lt;sub&gt;2&lt;/sub&gt; flux over the agroforestry and monoculture agricultural system. We aim to further improve the quality of the CO&lt;sub&gt;2&lt;/sub&gt; fluxes, by adapting post-processing software to better estimate the difference in carbon uptake between the agroforestry and monoculture systems.&lt;/p&gt;

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