Beware of effects on isotopes of dissolved oxygen during storage of natural iron‐rich water samples: A technical note. (21st January 2021)

• Record Type: Journal Article
• Authors: Köhler, Inga; Piatka, David; Barth, Johannes A.C.; Martinez, Raul E.
• Is Part Of: Rapid communications in mass spectrometry. Volume 35:Number 6(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-01-21
• Subjects: Mass spectrometry -- Periodicals; 543.65
• DOI: 10.1002/rcm.9024
• Languages: English
• ISSNs: 0951-4198

Abstract

Abstract : Rationale: Investigations of the isotope ratios of dissolved oxygen (δ 18 ODO ) provide valuable information about the oxygen cycle in aquatic systems. However, oxidation of Fe(II) may change pristine δ 18 ODO values during storage and can lead to a misinterpretation. We sampled an Fe(II)‐rich spring system and measured δ 18 ODO values at various time intervals in order to determine influences of Fe‐oxidation. Methods: Water samples were collected from an Fe‐rich spring and related stream and the δ 18 ODO values were measured in fresh, 4‐ and 13‐day‐old samples with an isotope ratio mass spectrometer. Three replicates were measured for each sample with a 1σ of ± 0.2‰. On‐site parameters and Fe(II) contents were also measured over the course of the spring system by multi‐parameter probes and spectrophotometry. Results: The δ 18 ODO values over the course of the spring system in fresh, 4‐ and 13‐day‐old samples revealed differences of up to 8‰. We explain this increase by the consumption of DO by Fe(II)‐oxidation. After a flow length of 85 m the differences in δ 18 ODO values between fresh and older samples decreased because most of the Fe(II) was consumed. Conclusions: False interpretations of δ 18 ODO values are possible if Fe‐rich water samples are measured after too long storage, and we recommend measurement immediately after sampling.