Gas transfer velocities of CO2 and CH4 in a tropical reservoir and its river downstream

Guerin, Frédéric; Abril, Gwénaël; Serça, D.; Delon, Claire; Richard, Sabine; Delmas, R.; Tremblay, Alain; Varfalvy, Louis

doi:10.1016/j.jmarsys.2006.03.019

Cited by 219 publications

(224 citation statements)

References 49 publications

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“…This in turn allows the computation of the ebullition CH 4 flux from the chamber CH 4 measurement that captures both ebullition and diffusive CH 4 fluxes. Chamber measurements have been assumed to provide biased k values 44 , although often comparing satisfactorily with atmospheric flux measurements 45,46 or infrared imaging of the water surface 47 . The obtained average k 600 in the Congo (12 ± 11 cm h −1 ) was not significantly different from the average in the Zambezi (10 ± 11 cm h −1 ) (unpaired t-test, p < 0.05).…”

Section: Ghg Flux Computationsmentioning

confidence: 99%

Globally significant greenhouse-gas emissions from African inland waters

et al. 2015

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Carbon dioxide emissions to the atmosphere from inland waters-streams, rivers, lakes and reservoirs-are nearly equivalent to ocean and land sinks globally. Inland waters can be an important source of methane and nitrous oxide emissions as well, but emissions are poorly quantified, especially in Africa. Here we report dissolved carbon dioxide, methane and nitrous oxide concentrations from 12 rivers in sub-Saharan Africa, including seasonally resolved sampling at 39 sites, acquired between 2006 and 2014. Fluxes were calculated from published gas transfer velocities, and upscaled to the area of all sub-Saharan African rivers using available spatial data sets. Carbon dioxide-equivalent emissions from river channels alone were about 0.4 Pg carbon per year, equivalent to two-thirds of the overall net carbon land sink previously reported for Africa. Including emissions from wetlands of the Congo river increases the total carbon dioxide-equivalent greenhouse-gas emissions to about 0.9 Pg carbon per year, equivalent to about one quarter of the global ocean and terrestrial combined carbon sink. Riverine carbon dioxide and methane emissions increase with wetland extent and upland biomass. We therefore suggest that future changes in wetland and upland cover could strongly a ect greenhouse-gas emissions from African inland waters.C limate predictions necessitate a full and robust account of natural and anthropogenic greenhouse-gas (GHG) fluxes, especially for CO 2 (refs 1-3), CH 4 (ref. 4) and N 2 O (ref. 5), which together accounted for 94% of the anthropogenic global radiative forcing by well-mixed GHGs in 2011 relative to 1750 (ref. 6). Inland waters (streams, rivers, lakes and reservoirs) are increasingly recognized as important sources of GHGs to the atmosphere, with global CO 2 and CH 4 emissions estimated at 2.1 PgC yr −1 (ref.3) and 0.7 PgC yr −1 (CO 2 -equivalents; CO 2 e) (ref. 4) (1 Pg = 10 15 g), respectively. Considering that the oceanic and land carbon (C) sinks correspond to ∼1.5 and ∼2.0 PgC yr −1 (ref. 7), respectively, the GHG flux from inland waters is significant in the global C budget.In a recent global compilation of inland CO 2 data 3 , <20 data points (out of 6,708, that is, <0.3%) represented African inland waters (with the exception of South Africa, which has been densely sampled), even though they account for ∼12% of both global freshwater discharge 8 and riverine surface area 3 , and include some of the largest rivers and lakes in the world. Equally for the global CH 4 database, there is a strong under-representation of tropical inland waters, whereby a recent synthesis 4 resorted to extrapolating CH 4 fluxes from temperate rivers.The prevailing large uncertainty involved in GHG flux estimates for inland waters, essentially due to the paucity of available data, is coupled to a poor understanding of underlying processes, both of which preclude gauging of future fluxes in response to human pressures. In particular, there is a need to further understand the link between inland water GHG fluxes and ...

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Section: Ghg Flux Computationsmentioning

confidence: 99%

Globally significant greenhouse-gas emissions from African inland waters

et al. 2015

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“…The air-water temperature difference reflected the thermal difference at the air-water interface. An increased air-water temperature difference promoted CO 2 emission from the reservoir surface under evaporative conditions due to the destabilization of the water surface (Guérin et al, 2007). For example, CO 2 flux was 4% higher under evaporative conditions in the Pacific Ocean (Ward et al, 2004).…”

Section: Environmental Variables Influencing Co 2 Fluxmentioning

confidence: 99%

Spatial and seasonal variability of CO2 flux at the air-water interface of the Three Gorges Reservoir

Yang¹,

Lu²,

Wang³

et al. 2013

Journal of Environmental Sciences

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Diffusive carbon dioxide (CO 2 ) emissions from the water surface of the Three Gorges Reservoir, currently the largest hydroelectric reservoir in the world, were measured using floating static chambers over the course of a yearlong survey. The results showed that the average annual CO 2 flux was (163.3 ± 117.4) mg CO 2 /(m 2 ·hr) at the reservoir surface, which was larger than the CO 2 flux in most boreal and temperate reservoirs but lower than that in tropical reservoirs. Significant spatial variations in CO 2 flux were observed at four measured sites, with the largest flux measured at Wushan (221.9 mg CO 2 /(m 2 ·hr)) and the smallest flux measured at Zigui (88.6 mg CO 2 /(m 2 ·hr)); these differences were probably related to the average water velocities at different sites. Seasonal variations in CO 2 flux were also observed at four sites, starting to increase in January, continuously rising until peaking in the summer (JuneAugust) and gradually decreasing thereafter. Seasonal variations in CO 2 flux could reflect seasonal dynamics in pH, water velocity, and temperature. Since the spatial and temporal variations in CO 2 flux were significant and dependent on multiple physical, chemical, and hydrological factors, it is suggested that long-term measurements should be made on a large spatial scale to assess the climatic influence of hydropower in China, as well as the rest of the world.

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“…The flux of gas from water to air (diffusive emissions) was calculated as the product of the gas exchange coefficient for the particular gas in question and the difference between gas concentrations in surface water and air (Equation 1). This approach involves more uncertainty in estimations of GHG emissions and is only used if floating chamber measurements are not possible (Guerin et al 2007, IHA 2010.…”

Section: Thin Boundary Layer Flux Calculationsmentioning

confidence: 99%

“…We estimated pre-impoundment river emissions using the measurements of emissions from free-flowing regions of the three major tributary rivers to the reservoir. These river emission rates were determined using the thin boundary layer method (see Guerin et al 2007, IHA 2010, due to boat access limitations and because the relatively high water velocities prevented use of the floating chamber.…”

Section: Pre-impoundment River Emissionsmentioning

confidence: 99%

“…But as others have reported (cf. Guerin et al, 2007), the fluxes of CO 2 to the atmosphere by tailwaters can be much greater than diffusive emissions of CO 2 from the reservoir surface. The tailwaters for Douglas Lake accounted for about 40% of the total emissions of CO 2 for the entire reservoir on an annual basis in 2010 (Table 1).…”

Section: Diffusive Emissions Of Co 2 and Ch 4 -Reservoir Tailwatersmentioning

confidence: 99%

See 1 more Smart Citation

Greenhouse Gas Emissions from U.S. Hydropower Reservoirs: FY2011 Annual Progress Report

Stewart¹,

Mosher²,

Mulholland³

et al. 2012

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Gas transfer velocities of CO2 and CH4 in a tropical reservoir and its river downstream

Cited by 219 publications

References 49 publications

Globally significant greenhouse-gas emissions from African inland waters

Globally significant greenhouse-gas emissions from African inland waters

Spatial and seasonal variability of CO2 flux at the air-water interface of the Three Gorges Reservoir

Greenhouse Gas Emissions from U.S. Hydropower Reservoirs: FY2011 Annual Progress Report

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