title: Robust optode-based method for measuring in situ oxygen profiles in gravelly streambeds.
abstract: One of the key environmental conditions controlling biogeochemical reactions in aquatic sediments like streambeds is the distribution of dissolved oxygen. We present a novel approach for the in situ measurement of vertical oxygen profiles using a planar luminescence-based optical sensor. The instrument consists of a transparent acrylic tube with the oxygen-sensitive layer mounted on the outside. The luminescence is excited and detected by a moveable piston inside the acrylic tube. Since no moving parts are in contact with the streambed, the disturbance of the subsurface flow field is minimized. The precision of the distributed oxygen sensor (DOS) was assessed by a comparison with spot optodes. Although the precision of the DOS, expressed as standard deviation of calculated oxygen air saturation, is lower (0.2-6.2%) compared to spot optodes (<0.1-0.6%), variations of the oxygen content along the profile can be resolved. The uncertainty of the calculated oxygen is assessed with a Monte Carlo uncertainty assessment. The obtained vertical oxygen profiles of 40 cm in length reveal variations of the oxygen content reaching from 90% to 0% air saturation and are characterized by patches of low oxygen rather than a continuous decrease with depth.
authors.affiliation: Department of Hydrogeology, UFZ - Helmholtz Centre for Environmental Research , Permoserstrasse 15, 04318 Leipzig, Germany. michael.vieweg@ufz.de
authors.forename: Michael
authors.initials: M
authors.lastname: Vieweg
authors.forename: Nico
authors.initials: N
authors.lastname: Trauth
authors.forename: Jan H
authors.initials: JH
authors.lastname: Fleckenstein
authors.forename: Christian
authors.initials: C
authors.lastname: Schmidt
mesh_terms: D004784:Environmental Monitoring / Q000379:methods*; D049449:Luminescence; D009010:Monte Carlo Method; D010100:Oxygen / Q000032:analysis*; D015203:Reproducibility of Results; D045483:Rivers / Q000737:chemistry*; D012680:Sensitivity and Specificity
chemical_list: D010100:Oxygen