Stable isotope biogeochemistry of the sulfur cycle in modern marine sediments: I. seasonal dynamics in a temperate intertidal sandy surface sediment

Abstract

A biogeochemical and stable isotope geochemical study was carried out in surface sediments of an organic-matter poor temperate intertidal sandy surface sediment (German Wadden Sea of the North Sea) to investigate the activity of sulfate-reducing bacteria and the dynamics of the vertical partitioning of sedimentary sulfur, iron, and manganese species in relation to the availability of total organic carbon (TOC) and mud contents. The contents and stable isotopic compositions ((34)S/(32)S) of total reduced inorganic sulfur species (TRIS) and dissolved sulfate were measured. Maximum oxygen penetration depths were estimated from the onset of a blackening of the sediments due to FeS accumulation and ranged from 5 to 10 mm below surface (mmbsf). A zone of relatively moderate relative organic-matter enrichment was found between 5 and 20 mmbsf leading to enhanced activities of sulfate-reducing bacteria with sulfate-reduction rates (SRR) up to 350 nmol cm(-3) d(-1). Below this zone, microbial SRR dropped significantly. Depth integrated SRR seem to depend not only on temperature but also on the availability of reactive organic matter. The sulfur-isotopic composition of TRIS was depleted in (34)S by 33-40 per thousand with respect to coexisting dissolved sulfate (constant at about +21 per thousand vs. Vienna-Canyon Diablo Troilite (V-CDT)). Since sulfate reduction is not limited by dissolved sulfate (open system), depth variations of the isotopic composition of TRIS reflect changes in overall isotope effect due to superimposed microbial and abiotic reactions. Most of the solid-phase iron and manganese was bonded to (non-reactive) heavy minerals. However, a layer of reactive Fe(III) and Mn(IV) oxi(hydroxi)des was found in the uppermost sediment section due to re-oxidation of dissolved Fe(II) and Mn(II) species at the sediment-water interface. Metal cycling below the surface is at least partially coupled to intense sulfur cycling.

Effect of temperature on biogeochemistry of marine organic-enriched systems: implications in a global warming scenario

“…All of these controlling factors typically have an interactive effect on sulfate reduction rates (Westrich andBerner 1988, Pomeroy andWiebe 2001). The fact that sulfate reduction rates show an exponential increase within the temperature regime typically found in coastal sediments (0-358C) has 3 E-mail: carsanz@um.es been verified in seasonal field studies (e.g., Kristensen et al 2000, Bottcher et al 2004, as well as in laboratory experiments (e.g., Finke andJorgensen 2008, Robador et al 2009). Similarly, sulfate reduction rates are greatly stimulated by the quality and quantity of deposited OM (Hansen et al 1993, Holmer andKristensen 1996).…”

“…Thus, sulfate reduction rates are also temperature dependent in surface sediments (Bottcher et al 2004, Al-Raei et al 2009). Sulfate-reducing bacteria usually have a respiration optimum 10-208C above their natural temperature regime (Isaksen andJorgensen 1996, Knoblauch andJorgensen 1999), so temperature is often a potentially limiting factor for sulfate-reducing bacteria (Pomeroy and Wiebe 2001).…”

“…The rates of sulfate reduction, i.e., the microbially mediated reduction of sulfate to sulfide, depends on temperature and the availability of reactive organic substrates and sulfate (Rusch et al 1998, Bottcher et al 2004, Al-Raei et al 2009). All of these controlling factors typically have an interactive effect on sulfate reduction rates (Westrich andBerner 1988, Pomeroy andWiebe 2001).…”

Seasonal dynamics of microbial sulfate reduction in temperate intertidal surface sediments: controls by temperature and organic matter

“…3; Böttcher et al 2000;Llobet-Brossa et al 2002). Bacterial aerobic and metal oxide-based mineralization as well as chemical recycling processes increase in importance at these sites due to the availability of enhanced amounts of metal oxides (Table 1; Böttcher et al 2000Böttcher et al , 2004. This indicates that the overall process according to Eq.…”

Sulfide intrusion in seagrasses assessed by stable sulfur isotopes—a synthesis of current results

“…Sulfide is produced during bacterial sulfate reduction and may accumulate in the sediment pore waters or precipitate with iron either as FeS or as pyrite (FeS 2 ) commonly referred to as the AVS (acid volatile sulfide) and the CRS (chromium reducible sulfur) pool, respectively, based on the method used for extraction of the precipitated pools (Fossing and Jørgensen, 1989). Sulfate is fractionated during sulfate reduction and sedimentary sulfide has δ 34 S ranging between −15 to −25 (Canfield, 2001;Böttcher et al, 2004), compared to about +21 for sulfate in oceanic seawater (Rees et al, 1978). This difference is sufficient to distinguish the sources of sulfur in seagrass tissues by analysis of the stable sulfur isotopic composition (Fry et al, 1982;.…”