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Beware of effects on isotopes of dissolved oxygen during storage of natural iron‐rich water samples: A technical note
Author(s) -
Köhler Inga,
Piatka David,
Barth Johannes A.C.,
Martinez Raul E.
Publication year - 2021
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.9024
Subject(s) - chemistry , isotope , environmental chemistry , oxygen , spring (device) , isotopes of oxygen , analytical chemistry (journal) , mass spectrometry , chromatography , nuclear chemistry , mechanical engineering , physics , organic chemistry , quantum mechanics , engineering
Rationale Investigations of the isotope ratios of dissolved oxygen (δ 18 O DO ) provide valuable information about the oxygen cycle in aquatic systems. However, oxidation of Fe(II) may change pristine δ 18 O DO values during storage and can lead to a misinterpretation. We sampled an Fe(II)‐rich spring system and measured δ 18 O DO 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 O DO 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 O DO 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 O DO values between fresh and older samples decreased because most of the Fe(II) was consumed. Conclusions False interpretations of δ 18 O DO values are possible if Fe‐rich water samples are measured after too long storage, and we recommend measurement immediately after sampling.