Sulfur marshes

The amounts and profile distribution of various sulfur forms in Louisiana coastal marshes are important in understanding sulfur cycling as related to the origin and type of tidal wetland marshes. Sulfur forms and distribution were determined in P. hemitomon freshwater marsh, a S. patens brackish marsh, and a S. alterniflora salt marsh along a salinity gradient in Barataria Basin, Louisiana. Soil samples were fractionated into acid volatile sulfur (AVS), elemental sulfur, HCl-soluble sulfur, pyrite sulfur, ester sulfate sulfur, carbon-bonded sulfur, and total sulfur (see Chapter 11 for details). 

Luther, GW., HI et ah Inorganic and Oiganic Sulfur Cycling in Salt-Marsh Poie Waters, Science. 232, 746 -749 (1986). 

Peterson, B. J., and R. W. Howarth. 1987. Sulfur, carbon, and nitrogen isotopes used to trace organic matter flow in the salt-marsh estuaries of Sapelo Island, Georgia. Limnology and Oceanography 32 1195-1213. 

The nitrogen cycle is closely connected with the fluxes of hydrogen, sulfur, and other chemicals (Smith et al., 1998 Dimitroulopoulou and Marsh, 1997 Chapin et al., 2002 Rhee et al., 2005 Stevenson and Cole, 1999). Nitrogen and hydrogen react under great pressure and temperature in the presence of a catalyst to make ammonia. The study of correlations between the cycles of these elements is necessary to improve... 

There have been a number of studies of biogenic emissions of sulfur gases other than H2S reported in the literature. Most of these have been concerned with high productivity sources, such as salt marshes and tidal areas and are summarized in Table II. 

Many of the previous direct flux measurements have focused on two distinct ecosystems, intertidal mudflats and Spartina altemiflora salt marshes. These coastal systems have the potential for large emissions of volatile reduced sulfur gases due to the availability of sulfate and organic matter. Intertidal mudflats (3.4) have a tendency towards anoxia, with concomitant production of H S via sulfate reduction. . altemiflora marshes (4T5) release DMS through the... 

Most of the emissions data available in the literature was obtained within alterniflora marshes, and hence reflect the complexity of this ecosystem. Our data set extends the available emissions data to less complex systems, and at the same time lowers our estimation of the biogenic contribution to atmospheric sulfur loading. Even our highest estimate of biogenic emissions, that of... 

The low emission rates measured in this study indicate that salt marshes are a minor source of sulfur to the global atmosphere. Furthermore, our measurement of deposition rates show the potential for losses to the same soil surfaces at times of elevated atmospheric concentration. 

Coastal wetlands have long been noted for their relatively high emission of volatile sulfur gases to the atmosphere indeed the typical odor of marshes often is due largely to DMS. Several studies have reported emissions of DMS, H2S, and other sulfur compounds, dimethyldisulfide, carbonyl sulfide, and carbon disulfide (10-12.40-42). DMS and H2S constitute the bulk of the flux, with DMS predominating in vegetated areas and H2S in mud flats. Fluxes of DMS... 

Bacterially produced elemental sulfur can also react with hydrogen sulfide form polysulnde ions. Thus, polysulfide ions should constitute a significant fraction of sulfur nudeophiles in reducing sediments especially where sulfide oxidation is incomplete, such as in intertidal and salt marsh sediments (31321. The polysulfide ions should also be important at redox boundaries (anoxic/ suboxic) in the water column of marine anoxic basins, such as the Black Sea. 

Reduced Sulfur Compounds in Marine Sediments. To determine the applicability of the bimane-HPLC technique to measure reduced sulfur compounds in sediment porewater samples, we compared the results of the methylene blue method of Cline (26). the DTNB procedure of Ellman (28) and the bimane-HPLC procedure outlined above. Cores included came from a Spartina foliosa marsh in Mission Bay (near San Diego, California), and an evaporation pond for the production of salt in south San Diego Bay (Table I). 

In marine and lacustrine muds, the initial sulfide phase precipitated during early diagenesis is mackinawite (FeS09) which is subsequently converted to greigite (Fe3S4) and pyrite (FeS2) (85-89). This reaction path leads to the formation of framboidal pyrite (88.90). However, in salt marsh sediments under low pH and low sulfide ion activity conditions, direct precipitation of pyrite by reaction of ferrous iron with elemental sulfur without the formation of iron monosulfides as intermediates has been reported (85-87.89.91.92). This reaction is one possible pathway for the precipitation of pyrite as single crystals (89). 

Tne question of the source molecule occurrence must be addressed. The coincidence in anaerobic environments of ammonia and reduced divalent sulfur species, which includes hydrogen sulfide, bisulfide anion and sulfide dianion, has been given adequate recognition. (See for example references 36,37.) The coincidence of polysulfide and ammonia has already been noted in an earlier part of this report (1). Polysulfide has been found in tidal and salt marsh sediments as well (38). 

Iron monosulfides show an antithetic relationship with pyritic sulfur (Table I). The highest amounts of acid volatile sulfides (which remained small compared to S in pyrite) occur directly beneath the marsh sediments within the upper portions of the tidal flat deposits. The high value for iron monosulfides in the upper part of the tidal creek sediments may be related to high rates of sulfate reduction at these depths. 

Marsh overprinting on the underlying sediments produced relatively high amounts of pyritic sulfur at shallow depths (100 to 203 cm). 

Stable sulfur isotopes can be effectively used to examine important geochemical processes associated with redox changes in sedimentary environments. For example, S042- reduction in salt marsh sediments yields isotopically depleted 534S porewater sulfide the uptake of H2S by marsh plants also results in isotopically depleted [Pg.173]

Gardner, L.R., Wolaver, T.G., and Mitchell, M. (1988) Spatial variations in the sulfur chemistry of salt marsh sediments at North Inlet, South Carolina. J. Mar. Res. 46, 815-836. 

Howarth, R.W. (1984) The ecological significance of sulfur in the energy dynamics of salt marsh and coastal sediments. Biogeochemistry 1, 5-27. 

King, G.M. (1988) Patterns of sulfate reduction and the sulfur cycle in a South Carolina salt marsh. Limnol. Oceanogr. 33, 376-390. 

King, GM., Howes, B.L., and Dacey, J.W.H. (1985) Short-term endproducts of sulfate reduction in a salt marsh the significance of acid volatile sulfide, elemental sulfur, and pyrite. Geochim. Cosmochim. Acta 49, 1561-1566. 

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