Greenhouse gas emissions from reservoirs of the western United States

Abstract

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 −2 d −1 ). Oroville (+1026 mg CO 2 m −2 d −1 ) and Shasta (+1247 mg CO 2 m −2 d −1 ) surfaces were also sources of CO 2 . In contrast, the surface of all the other reservoirs constituted sinks for CO 2 (from −349 to −1195 mg CO 2 m −2 d −1 ). Degassing fluxes ranged from +0.003 to +0.815 t CH 4 d −1 , and from +16 to +324 t CO 2 d −1 . Daily GHG budgets ranged from +0.146 to +2.228 t CH 4 d −1 , and from −15 to +224 t CO 2 d −1 . 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.