A new robust oxygen-temperature sensor for aquatic eddy covariance measurements

The fragility of thin Clark-type glass microelectrodes used in aquatic eddy covariance measurements of benthic oxygen fluxes is a challenge when using this powerful technique. This study presents a new fast-responding dual oxygen-temperature sensor for eddy covariance measurements that is far more robust. Response time tests in the lab, where the sensor was inserted from air into water, revealed 90% response times of 0.51 s and 0.34 s for oxygen and temperature measurements, respectively. In wave tank tests, the new sensor showed no stirring sensitivity in contrast to Clark-type microelectrodes. Other tests in a flume and in a particle-free water tank revealed how close the sensor can be positioned to the measuring volume of the Acoustic Doppler Velocimeter without disturbing velocity recordings. In field tests at river sites, all > 24 h, the new sensor recorded high-quality eddy covariance data for the entire deployment. Similar positive results were obtained in deployments at a marine site with unidirectional current flow overlaid with minor wave action. Concurrently deployed eddy covariance systems based on the new sensor and a traditional Clark-type microelectrode revealed that they recorded statistically equivalent fluxes and similar velocity-oxygen cospectra until the microelectrode broke after 2 h. The significant increase in robustness of the new sensor was achieved by relying on a larger sensor tip. This put some constrains on how the sensor should be deployed and fluxes extracted, but given the substantial gain in performance, it is a viable alternative for eddy covariance measurements in many aquatic environments.