Simple, robust eddy correlation amplifier for aquatic dissolved oxygen and hydrogen sulfide flux measurements

Abstract

The aquatic application of the eddy correlation (EC) technique is growing more popular and is gradually becoming a standard method for resolving benthic O 2 fluxes. By including the effects of the local hydrodynamics, the EC technique provides greater insight into the nature of benthic O 2 exchange than traditional methods (i.e., benthic chambers and lander microprofilers). The growing popularity of the EC technique has led to a greater demand for easily accessible and robust EC instrumentation. Currently, the EC instrumentation is limited to two commercially available systems that are still in the development stage. Here, we present a robust, open source EC picoamplifier that is simple in design and can be easily adapted to both new and existing acoustic Doppler velocimeters (ADV). The picoamplifier has a response time of < 0.1 ms and features galvanic isolation that ensures very low noise contamination of the signal. It can be adjusted to accommodate varying ranges of microelectrode sensitivity as well as other types of amperometric microelectrodes. We show that the extracted flux values are not sensitive to reduced microelectrode operational ranges (i.e., lower resolution) and that no signal loss results from using either a 16-or 14-bit analog-to-digital converter. Finally, we demonstrate the capabilities of the picoamplifier with field studies measuring both dissolved O 2 and H 2 S EC fluxes. The picoamplifier presented here consistently acquires high-quality EC data and provides a simple solution for those who wish to obtain EC instrumentation. The schematic of the amplifier's circuitry is given in the Web Appendix.

Ecosystem metabolism along a colonization gradient of eelgrass (Zostera marina) measured by eddy correlation

“…The eddy correlation instrument consisted of an acoustic Doppler velocimeter (ADV, Nortek-AS), coupled to a fastresponding (90% response time , 0.3 s) Clark-type O 2 microsensor (Unisense Science) via a submersible picoamp amplifier (McGinnis et al 2011). These sensors are selfcontained and mounted on a stainless steel tripod designed to minimize disturbance to the natural flow.…”

Benthic O2 uptake of two cold-water coral communities estimated with the non-invasive eddy correlation technique

“…The setup of the ECMs was similar to the original design by Berg et al (2003). The main components of the ECMs consisted of an acoustic Doppler velocimeter (ADV; Vector, Nortek) and Clark-type O 2 microelectrodes (Revsbech 1989) that relayed the signal to the ADV via submersible amplifiers (McGinnis et al 2011). The O 2 electrodes had 90% response times of 0.5 s while the stirring sensitivity was below 0.5% (Gundersen et al 1998).…”

“…The ADV recorded the velocity components as well as the O 2 microsensor signals at a frequency of 64 Hz and, in addition, collected ancillary information such as the sampling distance from the seabed, flow direction, and signal strength. Each ECM was mounted onto a small stainless steel tripod frame that was designed specifically for deployment by ROV (McGinnis et al 2011). A small conductivitytemperature-depth (CTD) logger equipped with an O 2 Aanderaa optode was mounted onto each ECM to collect background environmental information and for in situ calibration of the O 2 electrodes.…”

Benthic Carbon Mineralization and Nutrient Turnover in a Scottish Sea Loch: An Integrative In Situ Study

“…The main components consisted of an acoustic Doppler velocimeter (ADV, Vector, Nortek) and an O 2 microelectrode with the same measuring characteristics as described above. The O 2 microsensor signal was relayed to the ADV via a submersible amplifier (McGinnis et al 2011). The vertically aligned ADV recorded the longitudinal, traverse and vertical velocity components along with the output from the O 2 microsensor at a frequency of 32 Hz, which allowed full resolution of the current-driven turbulence transporting O 2 to the seafloor.…”