Greenhouse gas emissions from reservoirs of the western United States

Abstract

[1] Six reservoirs located in the Western United States (F. D. Roosevelt, Dworshak, Wallula, Shasta, Oroville, and New Melones) were sampled in order to estimate their greenhouse gas (GHG) emissions. Two types of fluxes were assessed: (1) diffusive fluxes of methane (CH 4 ) and carbon dioxide (CO 2 ) at the air/water interface and (2) degassing fluxes of CH 4 and CO 2 from water passing through the turbine spillways. Diffusive flux measurements indicated that the surface of the reservoirs were a source of CH 4 during the sampling period (from +3.2 to +9.5 mg CH 4 m À2 d À1 ). Oroville (+1026 mg CO 2 m À2 d À1 ) and Shasta (+1247 mg CO 2 m À2 d À1 ) surfaces were also sources of CO 2 . In contrast, the surface of all the other reservoirs constituted sinks for CO 2 (from À349 to À1195 mg CO 2 m À2 d À1 ). Degassing fluxes ranged from +0.003 to +0.815 t CH 4 d À1 , and from +16 to +324 t CO 2 d À1 . Daily GHG budgets ranged from +0.146 to +2.228 t CH 4 d À1 , and from À15 to +224 t CO 2 d À1 . Degassing fluxes represented an important term of these budgets. A significant correlation was observed between the magnitude of CO 2 diffusive fluxes and the water pH (R 2 = 0.81; p < 0.0001). All other correlations between GHG diffusive fluxes and independent variables tested were weak and/or not significant. Finally, while attempting to resolve the spatial variability in diffusive fluxes, we were able to cluster reservoirs neither according to geological nor ecological criteria.

Preliminary report on methane emissions from the Three Gorges Reservoir in the summer drainage period

“…The CH 4 emission fluxes from the water surface averaged (0.3305 ± 0.0940) mg CH 4 /(m 2 ·hr) from the beginning of June to the middle of October, which was very close to the annual average CH 4 emission fluxes of some temperate reservoirs in Canada (St. Louis et al, 2000) and the United States (Soumis et al, 2004), but about twice larger than the result of Zheng et al (2011a) in Ertan Reservoir. It should be noticed that water temperature is an important factor influencing CH 4 emissions from reservoirs (Soumis et al, 2004).…”

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

“…CO 2 flux decreased as pH increased, and atmospheric CO 2 was even absorbed at high pH values because high pH favored the formation of bicarbonate and led to the undersaturation of dissolved CO 2 in the water . The critical pH value for CO 2 absorption was 8.0-8.5 in boreal and temperate reservoirs (Soumis et al, 2004;Therrien et al, 2005;Tremblay et al, 2005). However, most of the CO 2 flux was positive in the study, probably because most of the pH values in the TGR ranged from 7.2 to 8.4, which did not surpass the abovementioned critical range.…”

“…However, algal blooms hardly occurred in the summer because of high water velocity in the mainstream of the TGR then (Xin et al, 2011). Negative CO 2 flux was often reported in other reservoirs in the world, such as the Três Marias Reservoir in Brazil (dos Santos et al, 2006), Petit Saut Reservoir in French Guiana (Abril et al, 2005), and F. D. Roosevelt, Dworshak, Wallula, and New Melones Reservoirs in the western United States (Soumis et al, 2004). These negative fluxes were possibly related to high phytoplankton activity.…”

“…turbines accounted for about 1.6%-7% of the total CO 2 emission and 1.5%-70% of the total CH 4 emission in a hydroelectric system (Soumis et al, 2004;Abril et al, 2005;Fearnside, 2005;Chanudet et al, 2011;Kemenes et al, 2011). Referring to these two proportions, the degassing emission at the turbine outflow of the TGR was estimated to be 0.006-0.135 Tg C/yr.…”

“…Respiration and primary production in the water column were strongly influenced by temperature, but the former was always reported to have a stronger response, thus resulting in a net increase in CO 2 production under warmer conditions (Mendonça et al, 2012). In addition, CO 2 flux was also reported to be influenced by pH (Soumis et al, 2004;Tremblay et al, 2005;Therrien et al, 2005), chlorophyll-a (Zhao et al, 2011), rainfall (Abril et al, 2005), and dissolved organic carbon (Tadonléké et al, 2005). Therefore, the spatiotemporal variations in CO 2 flux and their potential influencing factors need special attention in CO 2 emission from reservoirs.…”