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SUMMARY:The role of bioturbation in the carbon-sulfur-iron interplay- a le
 sson from salt marsh sediments - Gilad Antler\, University of Cambridge
DTSTART:20151009T100000Z
DTEND:20151009T110000Z
UID:TALK61655@talks.cam.ac.uk
CONTACT:Vicky Rennie
DESCRIPTION:Salt marshes are highly productive coastal wetlands that serve
  a critical role in carbon sequestration and nutrient trapping. In contras
 t to marine sediments that accumulate slowly over many thousands or millio
 ns of years\, salt marshes are highly dynamic transitional environments be
 tween the terrestrial and the marine realms. Because salt marshes are flus
 hed daily or monthly with seawater (with high concentrations of sulfate)\,
  our understanding is that the oxidation of organic carbon in salt marsh s
 ediments is dominated by microbial sulfate reduction\, similar to deeper m
 arine sediments. These high sulfate concentrations either inhibit methanog
 enesis or anaerobically oxidize any methane produced\; thus salt marshes a
 re not currently a large source of methane to the atmosphere\, unlike terr
 estrial wetlands. \n\nWe present pore fluid geochemical results from salt 
 marsh sediments in eastern England. The subsurface geochemistry can be div
 ided into two types\; ferruginous-sediments with very high ferrous iron co
 ncentrations (up to 2.5mM) and sulfidic-sediments with high dissolved sulf
 ide concentration (up to 8mM) and methane.  These two types of sediment ar
 e found as close as a few meters apart and are remarkably different in bot
 h geochemistry and sediment type and texture. We suggest that spatial vari
 ation in the ferrous-iron-rich saline groundwater creates two geochemicall
 y distinguishable sediments within the salt marsh. Where this saline water
  body is close to the surface\, the supply of ferrous iron allows bioturba
 tion by scavenging sulfide that would otherwise be toxic. This bioturbatio
 n enhances bioirrigation through which oxygen is supplied from the overlyi
 ng oxygenated water mixing with iron from the saline water body below. In 
 the aftermath of the bioturbation\, the sediment becomes organic-matter po
 or but sulfate- and iron-oxide rich.  In contrast\, in locations where the
  ferrous iron is depleted\, the sediment becomes toxic with excess dissolv
 ed sulfide and bioturbation is prevented. The end result in this case is s
 ediment that is methane and sulfide-rich and iron and sulfate poor.
LOCATION:Department of Earth Sciences - Harker II
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