Spatial Dependence of Gas Transfer Velocity in Boreal Reservoirs

Reservoirs are significant sources of greenhouse gases (GHG), but the magnitude of these emissions remains uncertain. The key to deriving robust diffusive fluxes is combining accurate surface water gas concentrations with realistic gas transfer velocities ( k 600 ). Existing models, primarily based on wind speed, estimate system‐wide k 600 values and typically do not transpose well between systems, particularly for reservoirs with complex shapes. This study aims to improve current models to estimate k 600 in such reservoirs. We focus on the La Romaine complex, composed of three cascading reservoirs (RO1, RO2, RO3) in northeastern Canada. We measured 535 carbon dioxide (CO 2 ) and methane (CH 4 ) fluxes using floating chambers during 11 field campaigns and calculated k 600 from these fluxes. Besides wind speed, within‐reservoir location related to depth and distance to shore strongly modulated k 600, but this location effect was reservoir‐dependent. Based on these three variables, we generated reservoir‐specific spatially explicit k 600 models that account for the heterogeneity in fetch within each reservoir. For RO1, our generated model explained up to 110% more of the variance in measured k 600 compared to any published system‐wide k 600 model to date, and for RO2 and RO3, up to 46% and 28%, respectively. We show that the same modeling framework can be applied to other reservoirs with complex shapes. Understanding how location within the reservoir modulates the influence of wind on k 600 will help constrain current reservoir GHG fluxes uncertainties.