Effect of sulfate availability on the isotopic signature of reduced sulfurous compounds in the sediments of a subtropical estuary
Journal
Wetlands
Journal Volume
32
Journal Issue
5
Pages
907-917
Date Issued
2012
Author(s)
Abstract
We examined spatial patterns of sulfate utility and δ34S signatures of sulfur species in sediments of a northern Taiwan subtropical estuary in December 2007. Results distinguished a sulfide-concentrated and freshwater-dominated site (called HR) in the upper estuary from two sulfateconcentrated and brackish-water-dominated sites (GR and GM) in the lower estuary. At the HR site, sulfide plays a crucial role in sulfur cycling. The δ34S signature of sulfur species suggests two source pools: one with depleted 34S as seen in pyrite-S (-8.9%), elemental sulfur (elemental-S, -8.6%), and organic sulfur (organic-S, -7.5%), and the other with enriched 34S as seen in acid-volatile sulfur (AVS, 6.9%). These signatures greatly differed from those predicted in an environment in which sulfate (+21%) is extremely limited, suggesting the relative importance of this isotopically light source. The two sites in the lower estuary were further differentiated: a mangrove-vegetated site (GM) had high elemental-S and pyrite-S concentrations, while a non-vegetated site (GR) had higher AVS and organic-S concentrations. These discrepancies may reflect the importance of mangrove vegetation in mediating sulfur speciation in estuarine sediments. At the GR and GM sites, the δ34S signature became enriched with increasing depth because of sulfate limitation. δ34S values of sulfur species in the deeper layer of the non-vegetated site varied with 34S enrichment, with remarkable enhancement to a value of 17.8% in AVS at a depth of 50 cm. Signatures of organic-S (9.8%) and pyrite-S (-1.1%) were also enriched. Such small fractionation, particularly in AVS, is likely to be associated with a sulfate deficiency in this lower estuarine area. © Society of Wetland Scientists 2012.
Subjects
Estuary; Geochemistry; Sediment; Stable isotope; Sulfur
Other Subjects
estuarine sediment; isotopic analysis; mangrove; sediment chemistry; spatiotemporal analysis; speciation (chemistry); subtropical region; sulfate; Taiwan
Type
journal article