Gas transfer velocity (k₆₀₀ increases with discharge in steep streams but not in low-slope streams

Gas transfer velocity ((Formula presented.)) controls gas fluxes between aquatic ecosystems and the atmosphere. In streams, (Formula presented.) is controlled by turbulence and, thus, local hydrology and geomorphology. Resultantly, variability in (Formula presented.) can be large and modeling (Formula presented.) from physical parameters can have large uncertainty. Here, we leverage a large dataset of (Formula presented.) estimates derived from tracer-gas experiments in 22 US streams across a range of discharges. Our analysis shows that (Formula presented.) was highly variable both spatially across and temporally within streams, with estimates of (Formula presented.) spanning three orders of magnitude. Overall, (Formula presented.) scaled with discharge in steep streams due to relatively high stream power, but not in low-slope streams, where stream power was relatively low even at high flows. Understanding how (Formula presented.) responds to stream discharge in a wide variety of streams is key to creating temporally and spatially resolved estimates of biogeochemical processes in streams.