Evaluating oxygen fluxes using microprofiles from both sides of the sediment–water interface

Lee D. Bryant, Daniel F. McGinnis, Claudia Lorrai, Andreas Brand, John C. Little, Alfred Wüest

Limnol. Oceanogr. Methods 8:610-627 (2010) | DOI: 10.4319/lom.2010.8.0610

ABSTRACT: Sediment–water fluxes are influenced by both hydrodynamics and sediment biogeochemical processes. However, fluxes at the sediment–water interface (SWI) are almost always analyzed from either a water- or sediment-side perspective. This study expands on previous work by comparing water-side (hydrodynamics and resulting diffusive boundary layer thickness, δDBL) and sediment-side (oxygen consumption and resulting sediment oxic zone) approaches for evaluating diffusive sediment oxygen uptake rate (JO2) and δDBL from microprofiles. Dissolved oxygen microprofile and current velocity data were analyzed using five common methods to estimate JO2 and δDBL and to assess the robustness of the approaches. Comparable values for JO2 and δDBL were obtained (agreement within 20%), and turbulence-induced variations in these parameters were uniformly characterized with the five methods. JO2 estimates based on water-side data were consistently higher (+1.8 mmol m–2 d–1 or 25% on average) and DBL estimates correspondingly lower (-0.4 mm or 35% on average) than those obtained using sediment-side data. This deviation may be attributed to definition of the sediment–water interface location, artifacts of the methods themselves, assumptions made on sediment properties, and/or variability in sediment oxygen-uptake processes. Our work emphasizes that sediment-side microprofile data may more accurately describe oxygen uptake at a particular location, whereas water-side data are representative of oxygen uptake over a broader sediment area. Regardless, our overall results show clearly that estimates of JO2 and δDBL are not strongly dependent on the method chosen for analysis.