Variable Physical Drivers of Near‐Surface Turbulence in a Regulated River

Inland waters, such as lakes, reservoirs and rivers, are important sources of climate forcing trace gases. A key parameter that regulates the gas exchange between water atmosphere is transfer velocity, which itself controlled by near-surface turbulence in water. While lakes reservoirs, mainly driven atmospheric forcing, shallow rivers streams it generated bottom friction gravity-forced flow. Large represent a transition these two cases. Near-surface has rarely been measured drivers have not quantified. We analyzed continuous measurements flow velocity quantified rate dissipation turbulent kinetic energy over ice-free season large regulated river Northern Finland. Measured rates agreed with predictions from bulk parameters, including mean wind speed, surface heat flux, one-dimensional numerical model. Values ranged to . Atmospheric or gravity was dominant driver for similar fraction time. variability occurred at diel time scales, when strongly affected downstream dam operation. By combining scaling relations boundary-layer bed air-water interface, we derived simple model estimating relative contributions speed function depth.