Köhler, Inga;
Martinez, Raul E.;
Piatka, David;
Herrmann, Achim J.;
Gallo, Arianna;
Gehringer, Michelle M.;
Barth, Johannes A. C.
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
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Medientyp:
E-Artikel
Titel:
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
Beteiligte:
Köhler, Inga;
Martinez, Raul E.;
Piatka, David;
Herrmann, Achim J.;
Gallo, Arianna;
Gehringer, Michelle M.;
Barth, Johannes A. C.
Beschreibung:
<jats:p>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 for rising dissolved oxygen
isotope compositions in the first 85 m of the system in the cold season
(February) and for the first 15 m during the warm season (May). Further
along the course of the stream, the δ18ODO decreased
towards values known for atmospheric equilibration around +24.6 ‰ during both seasons. Possible drivers for these changes may be reduced iron oxidation, increased atmospheric exchange and
DO production by oxygenic phototrophic algae mats. In the cold season, the
δ18ODO values stabilized around atmospheric equilibrium,
whereas in the warm season stronger influences by oxygenic photosynthesis caused values down to +21.8 ‰. In the warm season
from 145 m downstream of the spring, the δ18ODO
increased again until it reached atmospheric equilibrium. This trend can be
explained by respiratory consumption of DO combined with a relative
decrease in photosynthetic activity and increasing atmospheric influences.
Our study shows that dissolved Fe(II) can exert strong effects on the
δ18ODO of a natural circum-neutral spring system even
under constant supply of atmospheric O2. However, in the presence of
active photosynthesis, with supply of O2 to the system, direct
effects of Fe oxidation on the δ18ODO value become
masked. Nonetheless, critical Fe(II) concentrations may indirectly control
DO budgets by enhancing photosynthesis, particularly if cyanobacteria are
involved.
</jats:p>