Gas exchange rates for a first-order stream determined with deliberate and natural tracers

• Published in: Water resources research Vol. 26; no. 7
• Main Authors: Wanninkhof, R. (Columbia University, Palisades, NY), Mulholland, P.J, Elwood, J.W
• Format: Journal Article
• Language: English
• Published: 01.07.1990
• Subjects: AERACION; AERATION; AGUAS SUBTERRANEAS; COURS D'EAU; CURSOS DE AGUA; EAU SOUTERRAINE; ELEMENT CHIMIQUE; ELEMENTOS QUIMICOS; GASES; GAZ; ISOTOPE RADIOACTIF; RADIOISOTOPOS; TECHNIQUE DES TRACEURS; TECNICAS DE AISLAMIENTO DE ISOTOPOS; TENNESSEE; VELOCIDAD; VITESSE
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1029/WR026i007p01621

Gas transfer velocities have been determined for a first-order stream by performing a 3-hour release of the volatile tracer sulfur hexafluoride, SF6, and the nonvolatile tracer tritiated water, 3H2O. The average gas transfer velocity for the 292-m reach was 29 cm/h which corresponds to a reaeration coefficient for oxygen at 25 degrees C of 134 day-1. Groundwater inflow along the stream was corrected for by measuring the downstream dilution of the 3H2O spike. Downstream discharge increased from 0.5 L/s, 2 m downstream of the point of tracer release, to 19.3 L/s at a point 292 m downstream. As an alternative to using (radioactive) 3H2O, we investigated the possibility of using natural radon, 222Rn, as a groundwater tag and using the variation of SF6 and 222Rn along the stream to determine gas exchange rates and groundwater inflow. The method yielded an average transfer velocity of 21 cm/h and underestimated the groundwater inflow by a factor of 3. This large discrepancy is attributed to a doubling of stream discharge between the time the stream was sampled for radon and the tracer experiment and the limited number of radon samples