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 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 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.

scholarly journals Microbial drivers of methane emissions from unrestored industrial salt ponds

2021 ◽  
Author(s):  
Jinglie Zhou ◽  
Susanna M. Theroux ◽  
Clifton P. Bueno de Mesquita ◽  
Wyatt H. Hartman ◽  
Ye Tian ◽  
...  
Keyword(s):  
Microbial Communities ◽  
Methane Flux ◽  
Methane Emissions ◽  
Metagenomic Data ◽  
Rrna Gene ◽  
Salt Ponds ◽  
Salt Pond ◽  
Reference Wetlands ◽  
Reference Wetland ◽  
The Impact

AbstractWetlands are important carbon (C) sinks, yet many have been destroyed and converted to other uses over the past few centuries, including industrial salt making. A renewed focus on wetland ecosystem services (e.g., flood control, and habitat) has resulted in numerous restoration efforts whose effect on microbial communities is largely unexplored. We investigated the impact of restoration on microbial community composition, metabolic functional potential, and methane flux by analyzing sediment cores from two unrestored former industrial salt ponds, a restored former industrial salt pond, and a reference wetland. We observed elevated methane emissions from unrestored salt ponds compared to the restored and reference wetlands, which was positively correlated with salinity and sulfate across all samples. 16S rRNA gene amplicon and shotgun metagenomic data revealed that the restored salt pond harbored communities more phylogenetically and functionally similar to the reference wetland than to unrestored ponds. Archaeal methanogenesis genes were positively correlated with methane flux, as were genes encoding enzymes for bacterial methylphosphonate degradation, suggesting methane is generated both from bacterial methylphosphonate degradation and archaeal methanogenesis in these sites. These observations demonstrate that restoration effectively converted industrial salt pond microbial communities back to compositions more similar to reference wetlands and lowered salinities, sulfate concentrations, and methane emissions.

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 methane measurements at a Ponderosa pine plantation in California

2009 ◽  
Vol 9 (21) ◽  
pp. 8365-8375 ◽  
Author(s):  
C. J. P. P. Smeets ◽  
R. Holzinger ◽  
I. Vigano ◽  
A. H. Goldstein ◽  
T. Röckmann
Keyword(s):  
Eddy Covariance ◽  
Ponderosa Pine ◽  
Power Spectra ◽  
Methane Flux ◽  
Forest Site ◽  
Phase Lag ◽  
Closed Path ◽  
Pine Plantation ◽  
Model Calculations ◽  
Flux Measurements

Abstract. Long term methane flux measurements have been mostly performed with plant or soil enclosure techniques on specific components of an ecosystem. New fast response methane analyzers make it possible to use the eddy covariance (EC) technique instead. The EC technique is advantageous because it allows continuous flux measurements integrating over a larger and more representative area including the complete ecosystem, and allows fluxes to be observed as environmental conditions change naturally without disturbance. We deployed the closed-path Fast Methane analyzer (FMA) from Los Gatos Research Ltd and demonstrate its performance for EC measurements at a Ponderosa pine plantation at the Blodgett Forest site in central California. The fluctuations of the CH4 concentration measured at 10 Hz appear to be small and their standard deviation is comparable to the magnitude of the signal noise (±5 ppbv). Consequently, the power spectra typically have a white noise signature at the high frequency end (a slope of +1). Nevertheless, in the frequency range important for turbulent exchange, the cospectra of CH4 compare very well with all other scalar cospectra confirming the quality of the FMA measurements are good for the EC technique. We furthermore evaluate the complications of combined open and closed-path measurements when applying the Webb-Pearman-Leuning (WPL) corrections (Webb et al., 1980) and the consequences of a phase lag between the water vapor and methane signal inside the closed path system. The results of diurnal variations of CH4 concentrations and fluxes are summarized and compared to the monthly results of process-based model calculations.

scholarly journals Fetal Vibroacoustic Stimulation in Computerized Cardiotocographic Analysis: The Role of Short-Term Variability and Approximate Entropy

2012 ◽  
Vol 2012 ◽  
pp. 1-7 ◽  
Author(s):  
Maria Laura Annunziata ◽  
Mariamaddalena Scala ◽  
Natascia Giuliano ◽  
Salvatore Tagliaferri ◽  
Olga Carmela Maria Imperato ◽  
...  
Keyword(s):  
High Risk ◽  
Perinatal Outcomes ◽  
Approximate Entropy ◽  
Computer Assisted ◽  
Short Term ◽  
Fetal Movements ◽  
The Impact ◽  
Short Term Variability

The aim of this study was to evaluate the impact of vibroacoustic stimulation (VAS) on computerized cardiotocography short-term variability (STV) and approximate entropy (ApEn) in both low- and high-risk pregnancies. VAS was performed on 121 high- and 95 low-risk pregnancies after 10 minutes of continuous quiet, while their FHR parameters were monitored and recorded by cCTG analysis. Fetal heart rate was recorded using a computer-assisted equipment. Baseline FHR, accelerations, decelerations, STV, long-term irregularity (LTI), ApEn, and fetal movements (FMs) were calculated for defined observational periods before VAS and after 10 minutes. Data were also investigated in relationship with the perinatal outcome. In each group of patients, FHR after VAS remained almost unmodified. Fetal movements significantly increased after VAS in both groups. Results show that only in the high-risk pregnancies, the increase of STV and the decrease of ApEn after VAS were significantly associated with favorable perinatal outcomes.

SHORT-TERM VARIABILITY OF COASTAL ZONE HYDRODYNAMICS UNDER AN EXTERNAL FORCING: OBSERVATIONS AT THE BLACK SEA RESEARCH SITE OF SIO RAS

2017 ◽  
Author(s):  
Andrey Zatsepin ◽  
Andrey Zatsepin ◽  
Sergey Kuklev ◽  
Sergey Kuklev ◽  
Alexander Ostrovskii ◽  
...  
Keyword(s):  
Coastal Zone ◽  
The Black Sea ◽  
External Forcing ◽  
Short Term ◽  
Shirshov Institute ◽  
Open Sea ◽  
Observational Site ◽  
Upper Mixed Layer ◽  
The Impact ◽  
Short Term Variability

Since 2010, the P.P. Shirshov Institute of Oceanology RAS (SIO RAS) in Gelendzhik maintains the research (observational) site for year round multi-disciplinary studies and monitoring of the marine environment in the coastal zone. Analysis of the data obtained at the observational site revealed the existence of well pronounced short-term variability of coastal zone hydrodynamics at time scales from 1-3 days to 1-2 weeks. The paper examines the role of external forcing (including the impact of adjoined open sea dynamics and wind stress) in the short-term variability of hydrodynamics and upper mixed layer evolution.

scholarly journals Field intercomparison of two optical analyzers for CH<sub>4</sub> eddy covariance flux measurements

2010 ◽  
Vol 3 (4) ◽  
pp. 2961-2993 ◽  
Author(s):  
B. Tuzson ◽  
R. V. Hiller ◽  
K. Zeyer ◽  
W. Eugster ◽  
A. Neftel ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Best Practice ◽  
Field Evaluation ◽  
Methane Flux ◽  
Fast Response ◽  
Similar Data ◽  
Mixing Ratios ◽  
Data Treatment ◽  
Sonic Anemometers ◽  
Flux Measurements

Abstract. Fast response optical analyzers based on laser absorption spectroscopy are the preferred tools to measure field-scale mixing ratios and fluxes of a range of trace gases. Several state-of-the-art instruments have become commercially available and are gaining in popularity. This paper aims for a critical field evaluation and intercomparison of two compact, cryogen-free and fast response instruments: a quantum cascade laser based absorption spectrometer from Aerodyne Research, Inc., and an off-axis integrated cavity output spectrometer from Los Gatos Research, Inc. In this paper, both analyzers are characterized with respect to precision, accuracy, response time and also their sensitivity to water vapour. The instruments were tested in a field campaign to assess their behaviour under various meteorological conditions. The instrument's suitability for eddy covariance flux measurements was evaluated by applying an artificial flux of CH4 generated above a managed grassland with otherwise very low methane flux. This allowed an independent verification of the flux measurements accuracy, including the overall eddy covariance setup and data treatment. The retrieved fluxes were in good agreement with the known artificial emission flux, which is more than satisfactory, given that the analyzers were attached to separate sonic anemometers placed on individual eddy towers with different data acquisition systems but similar data treatment that are specific to the best practice used by the involved research teams.

scholarly journals Eddy covariance methane flux measurements over a grazed pasture: effect of cows as moving point sources

2015 ◽  
Vol 12 (12) ◽  
pp. 3925-3940 ◽  
Author(s):  
R. Felber ◽  
A. Münger ◽  
A. Neftel ◽  
C. Ammann
Keyword(s):  
Eddy Covariance ◽  
Methane Flux ◽  
Point Sources ◽  
Carbon Dioxide Exchange ◽  
Systematic Effect ◽  
Footprint Model ◽  
Grazed Pasture ◽  
Grazing System ◽  
Methane Fluxes ◽  
Flux Measurements

Abstract. Methane (CH4) from ruminants contributes one-third of global agricultural greenhouse gas emissions. Eddy covariance (EC) technique has been extensively used at various flux sites to investigate carbon dioxide exchange of ecosystems. Since the development of fast CH4 analyzers, the instrumentation at many flux sites has been amended for these gases. However, the application of EC over pastures is challenging due to the spatially and temporally uneven distribution of CH4 point sources induced by the grazing animals. We applied EC measurements during one grazing season over a pasture with 20 dairy cows (mean milk yield: 22.7 kg d−1) managed in a rotational grazing system. Individual cow positions were recorded by GPS trackers to attribute fluxes to animal emissions using a footprint model. Methane fluxes with cows in the footprint were up to 2 orders of magnitude higher than ecosystem fluxes without cows. Mean cow emissions of 423 ± 24 g CH4 head−1 d−1 (best estimate from this study) correspond well to animal respiration chamber measurements reported in the literature. However, a systematic effect of the distance between source and EC tower on cow emissions was found, which is attributed to the analytical footprint model used. We show that the EC method allows one to determine CH4 emissions of cows on a pasture if the data evaluation is adjusted for this purpose and if some cow distribution information is available.

Sign in / Sign up

Export Citation Format

Share Document