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Controls on sulfate reduction and sulfur isotope fractionation by natural microbial communities in sediments from the Schelde Estuary, The Netherlands
Stam, M.C.; Mason, P.R.D.; Laverman, A.M.; Pallud, C.; Van Cappellen, P. (2010). Controls on sulfate reduction and sulfur isotope fractionation by natural microbial communities in sediments from the Schelde Estuary, The Netherlands, in: Stam, M. Sulfur isotopes as a tracer for biogenic sulfate reduction in natural environments - A link between modern and ancient ecosystems. Geologica Ultraiectina, 316: pp. 41-64
In: Stam, M. (2010). Sulfur isotopes as a tracer for biogenic sulfate reduction in natural environments - A link between modern and ancient ecosystems. Geologica Ultraiectina, 316. PhD Thesis. Utrecht University, Faculty of Geosciences: Utrecht. ISBN 978-90-5744-178-3. 184 pp., more
In: Geologica Ultraiectina. Universiteit Utrecht: Utrecht, more

Available in Authors 
Document type: Dissertation

Authors  Top 
  • Stam, M.C., more
  • Mason, P.R.D.
  • Laverman, A.M.
  • Pallud, C.
  • Van Cappellen, P., more

Abstract
    Stable sulfur isotopes are potential tracers of microbial activity with numerous geological and environmental applications. Here, I report concurrent measurements of potential sulfate reduction rates (SRRs) and 34S/32S isotope fractionation effects (e) obtained with flowthrough reactors containing intact, 2 cm thick, sediment slices sampled from an unvegetated, intertidal site adjoining a salt marsh along the Schelde Estuary, The Netherlands. A total of 30 reactors were run with sediments sampled in February, May and October 2006. The effects of incubation temperature (10, 20, 30 and 50°C), sediment depth (0-2, 4-6 and 8-10 cm), distance from the vegetated marsh and sampling time were systematically investigated. Sulfate was supplied in non-limiting concentrations via the reactor inflow solutions. No external electron donor was supplied. Data analysis was restricted to SSR and isotope fractionation effects (e) obtained under steady state conditions. Values of e were derived from the measured differences in sulfate d34S between in- and outflow of the reactors. Potential SRRs varied over one order of magnitude (5 to 49 nmol cm-3 h-1) and were highest in the 30°C incubations. SRRs systematically decreased with depth, and were highest in the sediments collected closest to the vegetated marsh. Steady state isotope fractionation effects (e) ranged from 9 to 34 ‰ and exhibited an inverse relationship with SRR, as predicted by the standard fractionation model for enzymatic sulfate reduction of Rees (1973). The e versus SRR relationship, however, varied between sampling times, with higher e values measured in February, at comparable SRRs, than in May and October. The observed e versus SRR relationships also deviated from the previously reported inverse trend for sediments collected in a marine lagoon in Denmark (Canfield, 2001b). Thus, isotope fractionation during sulfate reduction is not uniquely determined by SRR, but is site and season specific. Possible factors affecting the e versus SRR relationship include the community structure and abundance of sulfate reducers, and the nature and accessibility of organic substrates. The data imply that small ranges in sulfur isotope fractionation (e = 15 ‰) observed in the environment may be indicative of biogenic processes, reflecting high sulfate reducing activity.

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