Oxygen-Carbon Method for Measuring Gas Exchange Rate in Streams

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Gas exchange rates between streams and the atmosphere are critically important to measurement of in-stream ecologic processes, as well as fate and transport of hazardous pollutants such as mercury and PCBs.  Methods to estimate gas exchange rates include empirical relations to hydraulics, and direct injection of a tracer gas such as propane. Empirical relations are inconsistent and inaccurate, particularly for lower order, high-roughness streams.  Gas injections are labor-intensive, and the gas exchange rate changes with discharge and stream geometry.  We propose a novel method for calculation of gas exchange rates utilizing O₂, pCO₂, pH, and temperature data. Gas exchange rates are calculated from a solution to the transport equations for oxygen and dissolved inorganic carbon. Collection of these data is increasingly common and continuous over the long term. The method can therefore be used to measure gas exchange rates through time, and can be automated for interactivity with databases.