Preprints
https://doi.org/10.5194/bg-2021-68
https://doi.org/10.5194/bg-2021-68

  22 Mar 2021

22 Mar 2021

Review status: this preprint is currently under review for the journal BG.

How are oxygen budgets influenced by dissolved iron and growth of oxygenic phototrophs in an iron-rich spring system? Initial results from the Espan Spring in Fürth, Germany

Inga Köhler1, Raul E. Martinez2, David Piatka1, Achim J. Herrmann3, Arianna Gallo3, Michelle M. Gehringer3, and Johannes A. C. Barth1 Inga Köhler et al.
  • 1Department of Geography and Geosiences, GeoZentrum Nordbayern, Friedrich-Alexander-Universität FAU, Erlangen, 91054, Germany
  • 2Max-Planck-Institute for Biogeochemistry, Jena, 07745, Germany
  • 3Division of Microbiology, Technische Universität, Kaiserslautern, 67663 Germany

Abstract. At present most knowledge on the impact of iron on 18O / 16O ratios (i.e. δ18O) of dissolved oxygen (DO) under circum-neutral conditions stems from experiments carried out under controlled laboratory conditions. These showed that iron oxidation leads to an increase in δ18ODO values. Here we present the first study on effects of elevated Fe(II) concentrations on the δ18ODO in a natural, iron-rich circum-neutral watercourse. Our results show that iron oxidation was the major factor dominating the oxygen isotopes in the first 85 meters of the system in the cold season (December/February) and for the first 15 meters during the warm season (May). This trend existed despite a constant oxygen supply from the atmosphere. Further along the course of a spring and associated small stream system, the δ18ODO decreased towards values known for atmospheric equilibration. This may be due to reduced iron oxidation, increased atmospheric exchange and photosynthetic DO production. The presence of oxygenic phototrophic mats suggested their involvement in the observed decrease in δ18ODO values. In the cold season, the δ18ODO values stabilized around atmospheric equilibrium at +24.6 ‰, whereas in the warm season values decreased to +21.8 ‰. This suggests stronger influences by oxygenic photosynthesis. About 145 meters downstream of the spring, the δ18ODO increased again in the warm season until it reached the atmos-pheric equilibrium value of +24.6 ‰. This trend can be explained by a respiratory consumption of DO combined with a decrease in photosynthetic activity. Our study shows that dissolved Fe(II) can exert strong effects on the δ18ODO of a natural circum-neutral spring system even though a constant supply of atmospheric oxygen occurs. In the presence of active photosynthesis, with active supply of oxygen to the system, direct effects of Fe oxidation on the δ18ODO value becomes masked. However, critical Fe(II) concentrations may indirectly control DO budgets by enhancing photosynthesis, particularly if cyanobacteria are involved.

Inga Köhler et al.

Status: open (until 06 May 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-68', Anonymous Referee #1, 02 Apr 2021 reply
  • RC2: 'Comment on bg-2021-68', Anonymous Referee #2, 14 Apr 2021 reply

Inga Köhler et al.

Inga Köhler et al.

Viewed

Total article views: 242 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
192 44 6 242 18 1 2
  • HTML: 192
  • PDF: 44
  • XML: 6
  • Total: 242
  • Supplement: 18
  • BibTeX: 1
  • EndNote: 2
Views and downloads (calculated since 22 Mar 2021)
Cumulative views and downloads (calculated since 22 Mar 2021)

Viewed (geographical distribution)

Total article views: 224 (including HTML, PDF, and XML) Thereof 224 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 15 Apr 2021
Download
Short summary
We investigated how high Fe(II)-levels influence the O2 budget of a circumneutral Fe(II) rich spring and whether a combined study of dissolved O2 and its isotopic composition can help asses this effect. We showed that dissolved Fe(II) can exert strong effects on the δ18ODO even though a constant supply of atmospheric O2 occurs. In the presence of photosynthesis, direct effects of Fe oxidation become masked. Critical Fe(II) concentrations indirectly control the DO by enhancing photosynthesis.
Altmetrics