Air-water oxygen exchange in a large whitewater river

Air–water gas exchange governs fluxes of gas into and out of aquatic ecosystems. Knowing this flux is necessary to calculate gas budgets (i.e., O₂) to estimate whole‐ecosystem metabolism and basin‐scale carbon budgets. Empirical data on rates of gas exchange for streams, estuaries, and oceans are readily available. However, there are few data from large rivers and no data from whitewater rapids. We measured gas transfer velocity in the Colorado River, Grand Canyon, as decline in O₂ saturation deficit, 7 times in a 28‐km segment spanning 7 rapids. The O₂ saturation deficit exists because of hypolimnetic discharge from Glen Canyon Dam, located 25 km upriver from Lees Ferry. Gas transfer velocity (k₆₀₀) increased with slope of the immediate reach. k₆₀₀ was