Aquatic Eddy Correlation: Quantifying the Artificial Flux Caused by Stirring-Sensitive O2 Sensors.
| Type | Article | ||||||||
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| Date | 2015-01 | ||||||||
| Language | English | ||||||||
| Author(s) | Holtappels Moritz 1, 2, Noss Christian3, Hancke Kasper4, 5, Cathalot Cecile6, McGinnis Daniel F.7, 8, Lorke Andreas3, Glud Ronnie N.4, 5, 9, 10, 11 |
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| Affiliation(s) | 1 : Max Planck Inst Marine Microbiol, Biogeochem Grp, Bremen, Germany. 2 : Univ Bremen, MARUM Ctr Marine Environm Sci, D-28359 Bremen, Germany. 3 : Univ Koblenz Landau, Inst Environm Sci, Landau, Germany. 4 : Univ Southern Denmark, Inst Biol, Odense, Denmark. 5 : Univ Southern Denmark, Nord Ctr Earth Evolut NordCEE, Odense, Denmark. 6 : Royal Netherland Inst Sea Res NIOZ, Yerseke, Netherlands. 7 : IGB Leibniz Inst Freshwater Ecol & Inland Fisheri, Expt Limnol, Berlin, Germany. 8 : Univ Geneva, Fac Sci, Inst FA Forel, Geneva, Switzerland. 9 : Aarhus Univ, Arctic Res Ctr, Aarhus, Denmark. 10 : Scottish Assoc Marine, Scottish Marine Inst, Oban, Argyll, Scotland. 11 : Greenland Climate Res Ctr, Greenland Inst Nat Resources, Nuuk, Greenland. |
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| Source | Plos One (1932-6203) (Public Library Science), 2015-01 , Vol. 10 , N. 1 , P. e0116564 (20p.) | ||||||||
| DOI | 10.1371/journal.pone.0116564 | ||||||||
| WOS© Times Cited | 33 | ||||||||
| Abstract | In the last decade, the aquatic eddy correlation (EC) technique has proven to be a powerful approach for non-invasive measurements of oxygen fluxes across the sediment water interface. Fundamental to the EC approach is the correlation of turbulent velocity and oxygen concentration fluctuations measured with high frequencies in the same sampling volume. Oxygen concentrations are commonly measured with fast responding electrochemical microsensors. However, due to their own oxygen consumption, electrochemical microsensors are sensitive to changes of the diffusive boundary layer surrounding the probe and thus to changes in the ambient flow velocity. The so-called stirring sensitivity of microsensors constitutes an inherent correlation of flow velocity and oxygen sensing and thus an artificial flux which can confound the benthic flux determination. To assess the artificial flux we measured the correlation between the turbulent flow velocity and the signal of oxygen microsensors in a sealed annular flume without any oxygen sinks and sources. Experiments revealed significant correlations, even for sensors designed to have low stirring sensitivities of ~0.7%. The artificial fluxes depended on ambient flow conditions and, counter intuitively, increased at higher velocities because of the nonlinear contribution of turbulent velocity fluctuations. The measured artificial fluxes ranged from 2 - 70 mmol m-2 d-1 for weak and very strong turbulent flow, respectively. Further, the stirring sensitivity depended on the sensor orientation towards the flow. For a sensor orientation typically used in field studies, the artificial flux could be predicted using a simplified mathematical model. Optical microsensors (optodes) that should not exhibit a stirring sensitivity were tested in parallel and did not show any significant correlation between O2 signals and turbulent flow. In conclusion, EC data obtained with electrochemical sensors can be affected by artificial flux and we recommend using optical microsensors in future | ||||||||
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