On Factors Controlling Air–Water Gas Exchange in a Large Tidal River
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Air–water gas exchange is an important process in aquatic systems, including tidal rivers and estuaries. While there are now reliable and routine methods for determining gas exchange over a range of temporal and spatial scales in the ocean and these measurements have resulted in widely used wind speed parameterizations to calculate air–sea gas exchange, the same has not been true for coastal inland waterways. Some studies have suggested that this difference is methodological, while others point to the existence of additional drivers for gas exchange besides wind in rivers and estuaries. Here, we present gas transfer velocities measured in the tidal Hudson River with a method widely used in oceanic studies, the 3He/SF6 dual tracer technique. Airside and waterside forcings were determined with an anemometer and an acoustic Doppler current profiler, respectively. The results confirm that wind is the dominant driver of gas exchange in the tidal Hudson River, with negligible contribution from bottom-generated turbulence. Furthermore, a parameterization between wind speed and gas exchange developed for the ocean is able to predict gas exchange in this environment with high accuracy. It is hoped that by transferring methodology used in oceanic studies to rivers and estuaries, robust data can be obtained that will eventually allow development of widely applicable relationships between easily measured environmental variables and gas exchange in tidal inland waters.
KeywordsAir–water gas exchange 3He/SF6 Hudson River
We thank S. Flores, T. Newberger, P. Schmieder, I. Sokoyanskaya, A. Spieler, and C. Zappa for assistance in the field; C. McNally for 3He extraction, B Turrin for 3He measurements; J. Clark for sharing data from the previous Hudson River dual tracer experiments; and F. Nitsche for providing the Hudson River geometry data. Special thanks are also given to J. Lipscomb, boat captain of Riverkeeper, whose knowledge of the Hudson River was indispensable to the project. Wind speed data for Dutchess County Airport was obtained from NOAA/NCDC. Funding was provided by the US Environmental Protection Agency (Grant # CR830976) and by the Dibner Fund. This is LDEO contribution no. 7461.
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