Robust optode-based eddy correlation systems for oxygen flux measurements in aquatic environments
Markus Huettel, Peter Berg
The aquatic eddy correlation technique can produce high-quality oxygen flux records due to its non-invasive nature, high temporal resolution, and ability to integrate over a large sediment surface area. No other existing flux method integrates these advantages. The main shortcoming of the technique is associated with the fragile oxygen microelectrode that often breaks or malfunctions and limits effective deployment times. This project is designed to solve this problem by producing robust eddy correlation technology and interpretation software for oxygen flux measurements. The requirements for these sensors are that they 1) can reliably measure oxygen concentrations over extended time periods in water with suspended particles and other matter, 2) can capture oxygen fluctuations caused by the eddies carrying the oxygen flux, and 3) do not distort turbulent eddies carrying the flux signal.
Durable optode eddy correlation systems can significantly improve the reliability of benthic oxygen flux estimates, a key parameter in local and global carbon budgets, and climate change studies. Existing flux estimates for shelf sediments rely mostly on short-term point measurements and typically exclude natural flow and light, thereby influencing transport processes, biogeochemical reactions, benthic photosynthesis and organism behavior. A robust eddy correlation instrument will be a powerful tool for measuring oxygen fluxes in such environments and will combine simple deployment and efficient collection of unbiased flux data. This will benefit both eddy correlation studies that typically include 24 h deployments, and future long-term monitoring of benthic systems, including underwater observatory platforms. It will also allow reliable collection of eddy correlation data in environments with high particle loads or in environments with strong currents and wave action as are frequently found on the continental shelf. An effective solution of the problems of microelectrode breakage and malfunctioning that appear to be overwhelming to many interested users will stimulate a substantially wider use of the approach. As a reference, in the atmospheric boundary layer, where similar sensor problems have been eliminated, the eddy correlation technique is the standard flux method today.
Berg, P., Long, M. H., Huettel, M., Rheuban, J.E., JcGlathery, K.J., Howarth, R.W., Foreman, K.H., Giblin, A.E., Marino, R. (2013). Eddy correlation measurements of oxygen fluxes in permeable sediments exposed to varying current flow and light. Limnology and Oceanography, 58(4), 2013, 1329–1343
Chipman, L., Huettel, M., Berg, P., Meyer, V., Klimant, I., Glud, R.N., Wenzhoefer, F. (2012), Oxygen optodes as fast sensors for eddy correlation measurements in aquatic systems, Limnology and Oceanography Methods, 10, 2012, 304–316
Berg, P., and Huettel, M. (2008) Monitoring the Seafloor Using the Noninvasive Eddy Correlation Technique: Integrated Benthic Exchange Dynamics, Oceanography 21, 164-167.
Berg, P. and others 2003. Oxygen uptake by aquatic sediments measured with a novel non-invasive eddy-correlation technique. Marine Ecology-Progress Series 261: 75-83.
Berg, P., H. Roy, and P. L. Wiberg. 2007. Eddy correlation flux measurements: The sediment surface area that contributes to the flux. Limnology and Oceanography 52: 1672-1684.
Canfield, D. E. and others 1993. Pathways of organic carbon oxidation in three continental margin sediments. Mar. Geol. 113: 27-40.
Nelson, J. R., J. E. Eckman, C. Y. Robertson, R. L. Marinelli, and R. A. Jahnke. 1999. Benthic microalgal biomass and irradiance at the sea floor on the continental shelf of the South Atlantic Bight: Spatial and temporal variability and storm effects. Continental Shelf Research 19: 477-505.