scholarly journals Eddy covariance flux measurements confirm extreme CH<sub>4</sub> emissions from a Swiss hydropower reservoir and resolve their short-term variability

2011 ◽  
Vol 8 (9) ◽  
pp. 2815-2831 ◽  
Author(s):  
W. Eugster ◽  
T. DelSontro ◽  
S. Sobek
Keyword(s):  
Greenhouse Gas ◽  
Eddy Covariance ◽  
Land Surface ◽  
Lake Level ◽  
Driving Forces ◽  
Open Water ◽  
Short Term ◽  
Flux Measurements ◽  
Floating Chamber ◽  
Hydropower Reservoir

Abstract. Greenhouse gas budgets quantified via land-surface eddy covariance (EC) flux sites differ significantly from those obtained via inverse modeling. A possible reason for the discrepancy between methods may be our gap in quantitative knowledge of methane (CH4) fluxes. In this study we carried out EC flux measurements during two intensive campaigns in summer 2008 to quantify methane flux from a hydropower reservoir and link its temporal variability to environmental driving forces: water temperature and pressure changes (atmospheric and due to changes in lake level). Methane fluxes were extremely high and highly variable, but consistently showed gas efflux from the lake when the wind was approaching the EC sensors across the open water, as confirmed by floating chamber flux measurements. The average flux was 3.8 ± 0.4 μg C m−2 s−1 (mean ± SE) with a median of 1.4 μg C m−2 s−1, which is quite high even compared to tropical reservoirs. Floating chamber fluxes from four selected days confirmed such high fluxes with 7.4 ± 1.3 μg C m−2 s−1. Fluxes increased exponentially with increasing temperatures, but were decreasing exponentially with increasing atmospheric and/or lake level pressure. A multiple regression using lake surface temperatures (0.1 m depth), temperature at depth (10 m deep in front of the dam), atmospheric pressure, and lake level was able to explain 35.4% of the overall variance. This best fit included each variable averaged over a 9-h moving window, plus the respective short-term residuals thereof. We estimate that an annual average of 3% of the particulate organic matter (POM) input via the river is sufficient to sustain these large CH4 fluxes. To compensate the global warming potential associated with the CH4 effluxes from this hydropower reservoir a 1.3 to 3.7 times larger terrestrial area with net carbon dioxide uptake is needed if a European-scale compilation of grasslands, croplands and forests is taken as reference. This indicates the potential relevance of temperate reservoirs and lakes in local and regional greenhouse gas budgets.

scholarly journals Eddy covariance flux measurements confirm extreme CH<sub>4</sub> emissions from a Swiss hydropower reservoir and resolve their short-term variability

2011 ◽  
Vol 8 (3) ◽  
pp. 5019-5055 ◽  
Author(s):  
W. Eugster ◽  
T. DelSontro ◽  
S. Sobek
Keyword(s):  
Greenhouse Gas ◽  
Eddy Covariance ◽  
Land Surface ◽  
Lake Level ◽  
Driving Forces ◽  
Open Water ◽  
Methane Flux ◽  
Short Term ◽  
Flux Measurements ◽  
Hydropower Reservoir

Abstract. Greenhouse gas budgets quantified via land-surface eddy covariance (EC) flux sites differ significantly from those obtained via inverse modeling. A possible reason for the discrepancy between methods may be our gap in quantitative knowledge of methane CH4 fluxes. In this study we carried out EC flux measurements during two intensive campaigns in summer 2008 to quantify methane flux from a hydropower reservoir and link its temporal variability to environmental driving forces: water temperature and pressure changes (atmospheric and due to changes in lake level). Methane fluxes were extremely high and highly variable, but consistently showed gas efflux from the lake when the wind was approaching the EC sensors across the open water, as confirmed by floating chamber flux measurements. The average flux was 3.76 ± 0.39 μg C m−2 s−1 (mean ± SE) with a median of 1.42 μg C m−2 s−1, which is quite high even compared to tropical reservoirs. Fluxes increased exponentially with increasing temperatures, but were decreasing exponentially with increasing atmospheric and/or lake level pressure. A multiple regression using lake surface temperatures (0.1 m depth), temperature at depth (10 m deep in front of the dam), atmospheric pressure, and lake level was able to explain 35.4 % of the overall variance. This best fit included each variable averaged over a 9-h moving window, plus the respective short-term residuals thereof. We estimate that an annual average of 3 % of the particulate organic matter (POM) input via the river is sufficient to sustain these large CH4 fluxes. To compensate the global warming potential associated with the CH4 effluxes from this hydropower reservoir a 1.3 to 3.7 times larger terrestrial area with net carbon dioxide uptake is needed, which indicates the potential relevance of temperate reservoirs and lakes in local and regional greenhouse gas budgets.

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

&lt;p&gt;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&lt;sub&gt;2&lt;/sub&gt;), 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&lt;sub&gt;2&amp;#160;&lt;/sub&gt;fluxes with bulk fluxes calculated using underway and surface bottle pCO&lt;sub&gt;2&lt;/sub&gt;&amp;#160;data.&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

scholarly journals Quantifying the impact of emission outbursts and non-stationary flow on eddy-covariance CH<sub>4</sub> flux measurements using wavelet techniques

2019 ◽  
Vol 16 (16) ◽  
pp. 3113-3131 ◽  
Author(s):  
Mathias Göckede ◽  
Fanny Kittler ◽  
Carsten Schaller
Keyword(s):  
Eddy Covariance ◽  
Methane Flux ◽  
Stationary Flow ◽  
Methane Emissions ◽  
Gap Filling ◽  
Short Term ◽  
Flux Measurements ◽  
Systematic Biases ◽  
The Impact ◽  
Short Term Variability

Abstract. Methane flux measurements by the eddy-covariance technique are subject to large uncertainties, particularly linked to the partly highly intermittent nature of methane emissions. Outbursts of high methane emissions, termed event fluxes, hold the potential to introduce systematic biases into derived methane budgets, since under such conditions the assumption of stationarity of the flow is violated. In this study, we investigate the net impact of this effect by comparing eddy-covariance fluxes against a wavelet-derived reference that is not negatively influenced by non-stationarity. Our results demonstrate that methane emission events influenced 3 %–4 % of the flux measurements and did not lead to systematic biases in methane budgets for the analyzed summer season; however, the presence of events substantially increased uncertainties in short-term flux rates. The wavelet results provided an excellent reference to evaluate the performance of three different gap-filling approaches for eddy-covariance methane fluxes, and we show that none of them could reproduce the range of observed flux rates. The integrated performance of the gap-filling methods for the longer-term dataset varied between the two eddy-covariance towers involved in this study, and we show that gap-filling remains a large source of uncertainty linked to limited insights into the mechanisms governing the short-term variability in methane emissions. With the capability for broadening our observational methane flux database to a wider range of conditions, including the direct resolution of short-term variability on the order of minutes, wavelet-derived fluxes hold the potential to generate new insight into methane exchange processes with the atmosphere and therefore also improve our understanding of the underlying processes.

scholarly journals Towards standards for measuring greenhouse gas fluxes from agricultural fields using instrumented towers

2006 ◽  
Vol 86 (3) ◽  
pp. 373-400 ◽  
Author(s):  
E. Pattey ◽  
G. Edwards ◽  
I B Strachan ◽  
R L Desjardins ◽  
S. Kaharabata ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Nitrous Oxide ◽  
Greenhouse Gas ◽  
Diode Laser ◽  
Eddy Covariance ◽  
Tunable Diode Laser ◽  
Trace Gas ◽  
Noise Characteristics ◽  
Short Period ◽  
Flux Measurements

This is a discussion of the available technology for measuring turbulent fluxes using instrumented towers. This review focuses on the flux measurements of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) for agricultural systems and the development of standards and protocols for measuring them. Agroecosystems present unique challenges because they undergo large leaf area index (LAI) and canopy architecture changes in a relatively short period of time (i.e., months) coupled with the fact that many of the greenhouse gas sources are diffuse. This review examines all aspects of the theory and application of the micrometeorological techniques, with focus on the flux gradient, eddy accumulation and eddy covariance techniques. Instrument placement, sens or response and noise characteristics are also explored. Innovative applications of micrometeorological methods are discussed for closed- and open-path trace gas sensors and commonly used meteorological instrumentation. The use of fast response single-pass optical tunable diode laser (i.e., CH4, N2O) and infrared gas analyzers (i.e., CO2, H2O) is described. Consideration is also taken of the trace gas sensors’flow system design, mixing ratio measurement, and data acquisition and reduction requirements for micrometeorological flux measurement. Procedures are outlined for the meteorological instrumentation necessary for eddy covariance-based energy budget measurement including ultrasonic anemometry. Key words: Tower-based greenhouse gas flux measurements, nitrous oxide, methane, carbon dioxide, tunable diode laser

scholarly journals Quantifying the impact of emission outbursts and non-stationary flow on eddy covariance CH<sub>4</sub> flux measurements using wavelet techniques

2019 ◽  
Author(s):  
Mathias Göckede ◽  
Fanny Kittler ◽  
Carsten Schaller
Keyword(s):  
Eddy Covariance ◽  
Methane Flux ◽  
Stationary Flow ◽  
Methane Emissions ◽  
Short Term ◽  
Flux Measurements ◽  
Systematic Biases ◽  
Wavelet Techniques ◽  
The Impact ◽  
Short Term Variability

Abstract. Methane flux measurements by the eddy-covariance technique are subject to large uncertainties, particularly linked to the partly highly intermittent nature of methane emissions. Outbursts of high methane emissions, termed event fluxes, hold the potential to introduce systematic biases into derived methane budgets, since under such conditions the assumption of stationarity of the flow is violated. In this study, we investigate the net impact of this effect by comparing eddy-covariance fluxes against a wavelet-derived reference that is not negatively influenced by non-stationarity. Our results demonstrate that methane emission events influenced 3–4 % of the flux measurements, and did not lead to systematic biases in methane budgets for the analyzed summer season; however, the presence of events substantially increased uncertainties in short-term flux rates. The wavelet results provided an excellent reference to evaluate the performance of three different gapfilling approaches for eddy-covariance methane fluxes, and we show that none of them could reproduce the range of observed flux rates. The integrated performance of the gapfilling methods for the longer-term dataset varied between the two eddy-covariance towers involved in this study, and we show that gapfilling remains a large source of uncertainty linked to limited insights into the mechanisms governing the short-term variability in methane emissions. With the capability to broaden our observational methane flux database to a wider range of conditions, including the direct resolution of short term variability at the order of minutes, wavelet-derived fluxes hold the potential to generate new insight into methane exchange processes with the atmosphere, and therefore also improve our understanding of the underlying processes.

scholarly journals ASSESSING GREENHOUSE GAS EXCHANGE OF AGRICULTURAL CROPS BY FLUX MEASUREMENTS IN THRACE PART OF TURKEY

AGROFOR ◽  
2019 ◽  
Vol 4 (1) ◽  
Author(s):  
Levent ŞAYLAN ◽  
Toprak ASLAN ◽  
Nilcan ALTINBAŞ ◽  
Serhan YEŞİLKÖY ◽  
Barış ÇALDAĞ ◽  
...  
Keyword(s):  
Gas Exchange ◽  
Greenhouse Gases ◽  
Greenhouse Gas ◽  
Eddy Covariance ◽  
Agricultural Crops ◽  
Eddy Covariance Method ◽  
Measurement And Analysis ◽  
Flux Measurements ◽  
Crop Variety ◽  
Agricultural Meteorology

Agriculture plays an important role in the global greenhouse gas (GHG) budget andits cycle. CO2 is one of the most important greenhouse gases, and plants releaseCO2 into the atmosphere by respiration and sink it by photosynthesis from theatmosphere. In addition, soil has an essential role in this exchange. Unfortunately,studies on the measurement of greenhouse gases above agricultural crops ininternationally accepted methods are not sufficient, especially in developingcountries. Thus, it is a clear need to determine carbon exchange of agriculturalcrops and activities (sink and emission) by taking into consideration of the specificconditions such as climate, crop variety, soil etc. Eddy Covariance (EC) is one ofthe widely used micrometeorological methods in the world for flux measurementstudies. Developments in measurement and analysis by instruments have allowedthis method to be applied more by researchers for the studies on GHG exchange. Inthis research, carbon exchanges (sink and emission) of watermelon grown inAtatürk Soil, Water and Agricultural Meteorology Research Institute located in theThrace part of Turkey, was measured using the Eddy Covariance method. Finally,estimated gas exchange above crops will be presented.

Rewet or not – insights on spatiotemporal patterns of greenhouse gas fluxes from soils in a rewetted Danish forested wetland

2020 ◽  
Author(s):  
Klaus Steenberg Larsen ◽  
Jesper Riis Christiansen
Keyword(s):  
Soil Carbon ◽  
Greenhouse Gas ◽  
Primary Source ◽  
Hydrological Regime ◽  
Open Water ◽  
Environmental Drivers ◽  
Forested Wetland ◽  
Flux Measurements ◽  
Spatio Temporal ◽  
The Impact

&lt;p&gt;Previously drained forested wetlands around the world are being restored for biodiversity, but our knowledge on the impact of restored hydrology on the total greenhouse gas (GHG) budget in these systems remains fragmented. Whereas the reduction in the net CO&lt;sub&gt;2&lt;/sub&gt; emission upon rewetting is well documented, the magnitude of the effect on the microbial production of CH&lt;sub&gt;4&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O is much more uncertain. This is partly because GHG fluxes, especially for CH&lt;sub&gt;4&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O, exhibit a highly dynamic spatiotemporal variation tied to the soil hydrological regime. To capture this variation properly a high number of flux measurements in time and space is needed, but many field studies are still highly limited in terms of their spatio-temporal coverage. This hiatus of field data is a primary source of uncertainty in model projections of impacts on the GHG budgets when restoring natural hydrology in drained wetlands.&lt;/p&gt;&lt;p&gt;We use a novel automatic chamber measurement system (SkyLine2D) connected to a Picarro G2508 analyzer for CO&lt;sub&gt;2&lt;/sub&gt;, CH&lt;sub&gt;4&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O flux measurements in a rewetted Danish forest wetland. With this system, we wish to resolve the little known spatio-temporal patterns of these GHGs and their relationship with environmental drivers such as soil moisture, water table, temperature, and soil carbon content. A total of 30 measurement plots, each measured 5 times per day over a period approaching 1 year (&gt; 40,000 measurements), were placed along a 30 meter transect covering a soil hydrological gradient including well-drained, waterlogged and open water conditions. The gradient also spans a soil carbon gradient increasing from well-drained mineral soils, over gleysols to waterlogged histosols.&lt;/p&gt;&lt;p&gt;Based on the novel, high-frequency flux data of CO&lt;sub&gt;2&lt;/sub&gt;, CH&lt;sub&gt;4&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O we will present a detailed analysis of the relationship with soil hydrology and temperature over periods spanning from hours to months. The data produced by this gradient approach combined with automated measurements represents an important step towards developing improved ecosystems models that can better predict the GHG effect of rewetting previously drained wetlands.&lt;/p&gt;

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

2014 ◽  
Vol 11 (15) ◽  
pp. 4225-4233 ◽  
Author(s):  
E. Podgrajsek ◽  
E. Sahlée ◽  
D. Bastviken ◽  
J. Holst ◽  
A. Lindroth ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Carbon Sink ◽  
Co2 Flux ◽  
Flux Footprint ◽  
Gas Fluxes ◽  
Flux Measurements ◽  
Eddy Covariance Measurements ◽  
Floating Chamber ◽  
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 chamber (FC) technique; however, several recent studies use the eddy covariance (EC) method. We present simultaneous flux measurements using both methods at 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.

Effects of strategic tillage on short-term erosion, nutrient loss in runoff and greenhouse gas emissions

Soil Research ◽  
2017 ◽  
Vol 55 (3) ◽  
pp. 201 ◽  
Author(s):  
A. R. Melland ◽  
D. L. Antille ◽  
Y. P. Dang
Keyword(s):  
Nitrous Oxide ◽  
Greenhouse Gas ◽  
Heavy Rainfall ◽  
Ghg Emissions ◽  
Nutrient Loss ◽  
Nitrous Oxide Emissions ◽  
Nutrient Losses ◽  
Short Term ◽  
Trade Offs ◽  
Carbon Dioxide Co2

Occasional strategic tillage (ST) of long-term no-tillage (NT) soil to help control weeds may increase the risk of water, erosion and nutrient losses in runoff and of greenhouse gas (GHG) emissions compared with NT soil. The present study examined the short-term effect of ST on runoff and GHG emissions in NT soils under controlled-traffic farming regimes. A rainfall simulator was used to generate runoff from heavy rainfall (70mmh–1) on small plots of NT and ST on a Vertosol, Dermosol and Sodosol. Nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) fluxes from the Vertosol and Sodosol were measured before and after the rain using passive chambers. On the Sodosol and Dermosol there was 30% and 70% more runoff, respectively, from ST plots than from NT plots, however, volumes were similar between tillage treatments on the Vertosol. Erosion was highest after ST on the Sodosol (8.3tha–1 suspended sediment) and there were no treatment differences on the other soils. Total nitrogen (N) loads in runoff followed a similar pattern, with 10.2kgha–1 in runoff from the ST treatment on the Sodosol. Total phosphorus loads were higher after ST than NT on both the Sodosol (3.1 and 0.9kgha–1, respectively) and the Dermosol (1.0 and 0.3kgha–1, respectively). Dissolved nutrient forms comprised less than 13% of total losses. Nitrous oxide emissions were low from both NT and ST in these low-input systems. However, ST decreased CH4 absorption from both soils and almost doubled CO2 emissions from the Sodosol. Strategic tillage may increase the susceptibility of Sodosols and Dermosols to water, sediment and nutrient losses in runoff after heavy rainfall. The trade-offs between weed control, erosion and GHG emissions should be considered as part of any tillage strategy.

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