UC Santa Barbara

Gas exchange across the air-water interface is a critical process that maintains adequate dissolved oxygen (DO) in the water column to support life. Oxygen reaeration rates can be accurately measured using deliberate gas tracers, like sulfur hexafluoride (SF6) or xenon (Xe). Two continuous release experiments were conducted in different creeks in the Sierra Nevada of California: Sagehen Creek in September, 2009, using SF6and Martis Creek in August, 2012, using both SF6and Xe. Measuring gas loss along the creek, which was approximated with the one-dimensional advection-dispersion equation, allows for the estimation of the SF6or Xe reaeration coefficient (KSF6, KXe), which is converted to DO reaeration (KDOor K2) using Schmidt numbers. Mean KSF6for upper and lower Sagehen and Martis Creeks were, respectively, 34 day-1, 37 day-1and 33 day-1, with corresponding KDOsof 61 day-1, 66 day-1and 47 day-1. In Martis Creek, KXewas slightly higher (21%) than KSF6, but the calculated KDOfrom SF6agreed with the calculated KDOfrom Xe within about 15%; this difference may be due to bubble-enhanced gas transfer. Established empirical equations of KDOusing stream characteristics did a poor job predicting KDO for both creeks. © 2014 by the authors.