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

Podgrajsek, Eva; Bastviken, David; Holst, Jutta; Lindroth, Anders; Tranvik, Lars J.; Rutgersson, Anna

doi:10.5194/bg-11-4225-2014

Cited by 80 publications

(80 citation statements)

References 42 publications

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“…During the stratified period, CO 2 fluxes were almost always higher when measured with FC than simultaneous EC measurements, as also found in Eugster et al (2003) and Podgrajsek et al (2014a) (statistical significance tested with Mann-Whitney U test, p < 0.05), although daily median values were, on average, higher when measured with EC than FC ( Table 2). Lower daily median FC fluxes might thus result from discontinuous FC measurements missing important episodic flux events, as suggested by Podgrajsek et al (2014a).…”

Section: Co 2 Flux Comparisonsupporting

confidence: 68%

“…Higher fluxes during the mixing period could have been more suitable for a comparison between the two methods. Podgrajsek et al (2014a) did not find systematically higher fluxes with EC or FC and found quite good agreement between these two methods for CH 4 fluxes. The EC method has a larger source area (flux footprint) than FC method, which might also affect the flux.…”

Section: Ch 4 Flux Comparisonmentioning

confidence: 68%

“…Lower daily median FC fluxes might thus result from discontinuous FC measurements missing important episodic flux events, as suggested by Podgrajsek et al (2014a). However, from the north side of the measurement raft (measurement spots N1-N4), FC fluxes do not differ statistically from EC CO 2 fluxes.…”

Section: Co 2 Flux Comparisonmentioning

confidence: 91%

“…During lake stratification, k CC gives the general flux level quite well, while during lake mixing and rain events it is clearly lower than the other measured fluxes. However, on an annual scale, these special occasions might contribute significantly to the CH 4 and CO 2 budgets Podgrajsek et al, 2014a;Miettinen et al, 2015) and should be noted in upscaled flux estimates.…”

Section: Co 2 Flux Comparisonmentioning

confidence: 99%

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Methane and carbon dioxide fluxes over a lake: comparison between eddy covariance, floating chambers and boundary layer method

et al. 2018

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Abstract. Freshwaters bring a notable contribution to the global carbon budget by emitting both carbon dioxide (CO 2 ) and methane (CH 4 ) to the atmosphere. Global estimates of freshwater emissions traditionally use a wind-speed-based gas transfer velocity, k CC (introduced by Cole and Caraco, 1998), for calculating diffusive flux with the boundary layer method (BLM). We compared CH 4 and CO 2 fluxes from BLM with k CC and two other gas transfer velocities (k TE and k HE ), which include the effects of water-side cooling to the gas transfer besides shear-induced turbulence, with simultaneous eddy covariance (EC) and floating chamber (FC) fluxes during a 16-day measurement campaign in September 2014 at Lake Kuivajärvi in Finland. The measurements included both lake stratification and water column mixing periods. Results show that BLM fluxes were mainly lower than EC, with the more recent model k TE giving the best fit with EC fluxes, whereas FC measurements resulted in higher fluxes than simultaneous EC measurements. We highly recommend using up-to-date gas transfer models, instead of k CC , for better flux estimates.BLM CO 2 flux measurements had clear differences between daytime and night-time fluxes with all gas transfer models during both stratified and mixing periods, whereas EC measurements did not show a diurnal behaviour in CO 2 flux. CH 4 flux had higher values in daytime than night-time during lake mixing period according to EC measurements, with highest fluxes detected just before sunset. In addition, we found clear differences in daytime and night-time concentration difference between the air and surface water for both CH 4 and CO 2 . This might lead to biased flux estimates, if only daytime values are used in BLM upscaling and flux measurements in general.FC measurements did not detect spatial variation in either CH 4 or CO 2 flux over Lake Kuivajärvi. EC measurements, on the other hand, did not show any spatial variation in CH 4 fluxes but did show a clear difference between CO 2 fluxes from shallower and deeper areas. We highlight that while all flux measurement methods have their pros and cons, it is important to carefully think about the chosen method and measurement interval, as well as their effects on the resulting flux.

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Section: Co 2 Flux Comparisonsupporting

confidence: 68%

Section: Ch 4 Flux Comparisonmentioning

confidence: 68%

Section: Co 2 Flux Comparisonmentioning

confidence: 91%

Section: Co 2 Flux Comparisonmentioning

confidence: 99%

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Methane and carbon dioxide fluxes over a lake: comparison between eddy covariance, floating chambers and boundary layer method

et al. 2018

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“…Chambers can be deployed for shorter time spans (15-60 min) in order to determine the gas flux, or they can be left to equilibrate with the CO 2 partial pressure of surface water (Natchimuthu et al, 2017). The equipment is relatively cheap and easy to use compared to other methods such as eddy-covariance (Podgrajsek et al, 2014;Jammet et al, 2017) or whole-lake addition of gas tracers (Cole and Caraco, 1998;Crusius and 25 Wanninkhof, 2003). The disadvantage, however, is the high work load required to repeatedly lift the chambers manually to evacuate the chamber headspace before each measurement of gas flux with the floating chamber resulting in few and discontinuous measurement series (Podgrajsek et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

A simple and cost-efficient automated floating chamber for continuous measurements of carbon dioxide gas flux on lakes

Martinsen¹,

Kragh²,

Sand‐Jensen³

2018

Preprint

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Abstract. Freshwaters emit significant amounts of CO 2 on a global scale. Yet, emissions remain poorly constrained from the diverse range of aquatic systems. The drivers and regulators of CO 2 gas flux from standing waters require further investigation to improve knowledge on both global scale estimates and system scale carbon balances. Often lake-atmosphere gas fluxes are estimated from empirical models of gas transfer velocity and air-water concentration gradient. Direct 10 quantification of the gas flux circumvents the uncertainty associated with the use of empirical models from contrasting systems. Existing methods to measure CO 2 gas flux are often expensive (e.g. eddy-covariance) or require a high workload in order to overcome the limitations of single point-measurements using floating chambers. We added a small air pump, timer and an exterior tube to ventilate the floating chamber headspace and passively regulate excess air pressure. By automating evacuation of the chamber headspace, continuous measurements of lake CO 2 gas flux can be obtained with minimal effort. 15We present the chamber modifications and an example of operation from a small forest lake. The modified floating chamber performed well in the field and enabled continuous measurements of CO 2 gas flux with 40-minute intervals. Combining the direct measurements of gas flux with measurements of air and waterside CO 2 partial pressure also enabled calculation of gas exchange velocity. Application of the described floating chamber is straightforward and modifications are both simple and cost-efficient to perform. Changing the chamber dimensions to particular applications and systems makes this approach to 20 measure gas flux flexible and appropriate in a range of different systems.

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Diel cycle of lake‐air CO₂ flux from a shallow lake and the impact of waterside convection on the transfer velocity

2015

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Two years of eddy covariance measurements of lake carbon dioxide (CO 2 ) fluxes reveal a diel cycle with higher fluxes during night. Measurements of partial pressure in the air (pCO 2a ) and in the water (pCO 2w ), during 4 months, show that the high nighttime fluxes are not explained by changes in the difference between pCO 2a and pCO 2w . Analyzing the transfer velocity (k 600,meas ), which is a measure of the efficiency of the gas transfer, with respect to wind speed, shows that variations in wind speed do not explain the diel cycle. During nighttime, when the fluxes are high, the wind is normally low. Thus, a solely wind-based parameterization of the transfer velocity (k u,CC ) results in large errors compared to k 600,meas , especially for wind speeds lower than 6 m s À1 . The mean absolute percentage error between k u,CC and k 600,meas is 79%.By subtracting k u,CC from k 600,meas , we investigate how waterside convection influence k 600,meas . Our results show that the difference (k 600,meas À k u,CC ) increases with increasing waterside convection. Separating the transfer velocity parameterization in two parts, one depending on the wind speed and one depending on waterside convection, the mean absolute percentage error compared to the measurements reduces to 22%. The results in this paper show that the high nighttime CO 2 fluxes can, to a large extent, be explained by waterside convection and that a transfer velocity parameterization based on both wind speed and waterside convection better fits the measurements compared to a parameterization based solely on wind speed.

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

Cited by 80 publications

References 42 publications

Methane and carbon dioxide fluxes over a lake: comparison between eddy covariance, floating chambers and boundary layer method

Methane and carbon dioxide fluxes over a lake: comparison between eddy covariance, floating chambers and boundary layer method

A simple and cost-efficient automated floating chamber for continuous measurements of carbon dioxide gas flux on lakes

Diel cycle of lake‐air CO₂ flux from a shallow lake and the impact of waterside convection on the transfer velocity

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

Cited by 80 publications

References 42 publications

Methane and carbon dioxide fluxes over a lake: comparison between eddy covariance, floating chambers and boundary layer method

Methane and carbon dioxide fluxes over a lake: comparison between eddy covariance, floating chambers and boundary layer method

A simple and cost-efficient automated floating chamber for continuous measurements of carbon dioxide gas flux on lakes

Diel cycle of lake‐air CO2 flux from a shallow lake and the impact of waterside convection on the transfer velocity

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Diel cycle of lake‐air CO₂ flux from a shallow lake and the impact of waterside convection on the transfer velocity