The relationship between near-surface turbulence and gas transfer velocity in freshwater systems and its implications for floating chamber measurements of gas exchange

We performed a series of gas exchange measurements in 12 diverse aquatic systems to develop the direct relationship between near-surface turbulence and gas transfer velocity. The relationship was log-linear, explained 78% of the variation in instantaneous gas transfer velocities, and was valid over a range of turbulent energy dissipation rates spanning about two orders of magnitude. Unlike wind-based relationships, our model is applicable to systems ranging in size from less than 1 km(2) to over 600 km(2). Gas fluxes measured with our specific model of floating chambers can be grossly overestimated (by up to 1000%), particularly in low-turbulence conditions. In high-turbulence regimes, flux overestimation decreases to within 50%. Direct measurements of turbulent energy dissipation rate provide reliable estimation of the associated gas transfer velocity even at short temporal and spatial scales.