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Air-water Gas Exchange Rates on a Large Impounded River Measured Using Floating Domes (Poster)
Citation:
REBHOLZ, J. AND J. BEAULIEU. Air-water Gas Exchange Rates on a Large Impounded River Measured Using Floating Domes (Poster). Presented at OLMS Spring Conference, Canton, OH, March 19, 2010.
Impact/Purpose:
To inform the public.
Description:
Mass balance models of dissolved gases in rivers typically serve as the basis for whole-system estimates of greenhouse gas emission rates. An important component of these models is the exchange of dissolved gases between air and water. Controls on gas exchange rates (K) have been well studied in streams, estuaries, and lakes, but few direct measurements of K have been made in large, impounded rivers. We employed a floating dome accumulation method to measure K in the Markland Pool of the Ohio River. Our objectives were to demonstrate the efficacy of the floating dome method, identify factors that control K, and test the accuracy of published gas exchange models. Our floating dome method proved to be simple and efficient. Gas exchange rates could be measures in a little as 9 minutes and several domes could be sampled simultaneously yielding replicated estimates. Our measured Ks averaged 15 cm/h (interquartile range 9.6–21.0 cm/h), within the expected range for a large river. Gas exchange rates estimated from the accumulation of CO2, N2O, and CH4 were correlated (0.33≤r2≤0.46), but CO2 yielded consistently lower rates. Variability among replicate K estimates increased with decreasing dissolved gas concentrations. Gas exchange rates were positively related to discharge and water velocity, but not wind speed. Published K models consistently underestimated the exchange rates measured in our system. Our conclusion is that gas exchange in large, impounded rivers is controlled by multiple factors and this complexity greatly hinders the development of gas exchange models for these systems.
