Methane Emissions from a Small Wind Shielded Lake Determined by Eddy Covariance, Flux Chambers, Anchored Funnels, and Boundary Model Calculations: A Comparison

Schubert, Carsten J.; Diem, Torsten; Eugster, Werner

doi:10.1021/es203465x

Cited by 148 publications

(167 citation statements)

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“…Monitoring and characterization of CH 4 and CO 2 fluxes in representative reservoirs of different power densities, locations and time since construction are critically needed to better quantify the total GHG emissions from the hydroelectric reservoirs in China. Although various sampling and analysis techniques have been used, measurement of GHG emissions from reservoirs -which can cover several hundreds of square kilometres and have depths exceeding 100 m -is a complicated process 30,31 . The limited number of sampling spots may not be able to represent the overall emissions from the reservoirs with complex hydrodynamics 23,30 .…”

Section: Discussionmentioning

confidence: 99%

The urgency of assessing the greenhouse gas budgets of hydroelectric reservoirs in China

Cheng

2013

Nature Clim Change

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NATURE CLIMATE CHANGE | VOL 3 | AUGUST 2013 | www.nature.com/natureclimatechange C hina overtook the United States and became the world's largest electricity producer and consumer in 2011. The total electricity generation reached 4,722 TW h in 2011, with thermal power and hydropower contributing to 82.5% and 14.0% of the generated electricity, respectively 1 . Meanwhile, over 90% of the thermal electricity is generated by highly polluting coal-fired generation, which had a high grid emission factor of 804 g CO 2 equivalent (CO 2 e) per kW h in 2010 2 . Coal-fired plants are not only the largest stationary source emitters of greenhouse gases (GHGs) in China, but they also bring serious air pollution problems with releases of SO 2 , NO x and fine particles. Hydropower, with more than 200 GW of total installed capacity, accounts for approximately 6% of the total energy supply and over 80% of all electricity generated from renewable sources in China. Joining the global efforts to combat climate change, China is committed to increase the share of non-fossil fuels in its total energy mix to 15% by 2020. Accordingly, the production capacity of hydropower should increase by, on average, 10 to 15 GW yr −1 to help achieve this goal. Cascades of dams are currently being built, planned or proposed on the major river valleys in southwest China, where over two-thirds of the country's hydroelectric resources are located (Fig. 1). With physical water scarcity, and spatially and temporarily uneven distribution of water resources 3 , reservoir development is also a key component of China's recent heavy investment in water infrastructures to adapt to climate change, droughts and floods, and to improve food security 4 .Although hydropower is widely claimed to be a 'clean' energy source, critics have long warned of the environmental impact of large hydroelectric projects. In particular, research over the past two decades has revealed that the decay of organic matter (OM) in reservoirs could release significant amounts of CO 2 and CH 4 , and the emissions from tropical reservoirs characterized by high levels of OM and shallow depths are much higher compared with those in boreal and temperate regions [5][6][7][8][9][10][11][12][13] . Methane is 25 times more effective at trapping heat in the atmosphere than CO 2 over a 100-year period, and is responsible for over 20% of the change in the radiative forcing of the climate system 14 . It has been estimated that large dams release approximately 104 Tg CH 4 annually, or 20% of the total emissions from natural and anthropogenic sources 15 , although current estimations on GHG emissions from global hydroelectric reservoirs bear large uncertainties 13,16 .Carbon dioxide, methane and nitrous oxide are the major GHGs that can be produced in reservoirs, but nitrous oxide emissions are The urgency of assessing the greenhouse gas budgets of hydroelectric reservoirs in China Yuanan Hu, Hefa Cheng* Already the largest generator of hydroelectricity, China is accelerating dam construction to increase ...

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Section: Discussionmentioning

confidence: 99%

The urgency of assessing the greenhouse gas budgets of hydroelectric reservoirs in China

Cheng

2013

Nature Clim Change

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“…Chambers and the EC methods are in relatively good agreement in these studies, and the discrepancy still observed is mainly due to spatial heterogeneity of the gas flux. Comparisons over water bodies are sparse (Eugster et al, 2011;Schubert et al, 2012), yet the results, only for CH 4 flux, show that the methods are of the same order of magnitude. Since both methods are widely used, further parallel studies with more direct comparisons are needed.…”

Section: Introductionmentioning

confidence: 99%

“…During recent years EC measurements have been made also over lakes, mainly for CO 2 flux (e.g. Eugster et al, 2003;Huotari et al, 2011;Jonsson et al, 2008;Vesala et al, 2006) but in a few cases also for CH 4 flux (Eugster et al, 2011;Sahlée et al, 2014;Schubert et al, 2012). The EC method yields continuous measurements with limited labour, but requires expensive instrumentations and extensive data post-processing.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2014

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Abstract. Fluxes of carbon dioxide (CO 2 ) and methane (CH 4 ) 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 CO 2 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 CO 2 (pCO 2w ) in the EC flux footprint. The methods agree better for CH 4 fluxes. It is, however, clear that short-term discontinuous FC measurements are likely to miss important high flux events.

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“…Because current upscaling estimates are based on these methods, comparison is needed to reduce the uncertainties in current estimates of the role of freshwaters in global carbon cycle. Such a comparison also gives valuable information on measurement technique development needs, and so far there is only one comparative study including all three methods for CH 4 in a temperate lake (Schubert et al, 2012). This is, to our knowledge, the first study including the three measurement methods for both CH 4 and CO 2 in a boreal lake, even though the boreal zone harbours a large fraction of the global lakes (Lehner and Döll, 2004;Verpoorter et al, 2014).…”

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confidence: 95%

“…According to recent studies, this upscaling approach strongly underestimates current emissions from lakes and improved methods are needed (e.g. Schubert et al, 2012;Mammarella et al, 2015). Heiskanen et al (2014) and Tedford et al (2014) suggest k models based also on heat flux and water turbulence measurements for more accurate estimates.…”

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confidence: 99%

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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Methane Emissions from a Small Wind Shielded Lake Determined by Eddy Covariance, Flux Chambers, Anchored Funnels, and Boundary Model Calculations: A Comparison

Cited by 148 publications

References 34 publications

The urgency of assessing the greenhouse gas budgets of hydroelectric reservoirs in China

The urgency of assessing the greenhouse gas budgets of hydroelectric reservoirs in China

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

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

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