Rates and controls of methane emission from four Pacific northwest reservoirs with contrasting management regimes

Abstract

Although collectively reservoirs constitute a globally significant source of anthropogenic methane (CH ₄ ), there are still few investigations of reservoir CH ₄ fluxes and their controls that span multiple seasons, years, and reservoir types. Here we present results from a 2‐yr study of diffusive and ebullitive CH ₄ fluxes in four contrasting reservoirs in the Pacific Northwest United States. Using floating chambers outfitted with CH ₄ sensors ( n  = 105), supported by gas chromatography and environmental monitoring, we identified chlorophyll a , water temperature, season, reservoir type (run‐of‐river vs. storage), and hydrostatic pressure fluctuations as significant predictors of CH ₄ flux. These findings indicate that water‐level fluctuations and chlorophyll a are associated with increased ebullitive flux in reservoir forebays, reinforce previous work demonstrating that neglecting ebullition can substantially underestimate total CH ₄ emissions, and highlight that strong seasonal variability necessitates full annual sampling to accurately constrain emission estimates.