Sulfate Reduction and Methanogenesis in the Sediment of a Saltmarsh on the East Coast of the United Kingdom

Abstract

The rates of sulfate reduction, methanogenesis, and methane loss were measured in saltmarsh sediment at monthly intervals. In addition, dissolved methane and sulfate concentrations together with pS2and pH were determined. Methane formation from carbon dioxide, but not from acetate, was detected within the same horizon of sediment where sulfate reduction was most active. Sulfate reduction was about three orders of magnitude greater than annual methanogenesis. The two processes were not separated either spatially or temporally, but occurred within the same layer of sediment at the same time of the year. Their coexistence did not seem to be the result of sulfate-depleted microenvironments within which methanogenesis could occur, but the methanogenic bacteria persisted at very low rates of activity within the same environment as the sulfate reducers. Sulfate reduction and methanogenesis are microbial processes of particular importance in anaerobic environments as they are major terminal oxidation steps in the flow of carbon and electrons. Cappenberg (8) demonstrated that the two processes were spatially separated in freshwater sediment, and Reeburgh and Heggie (21), in a review of the available data, reported that in marine sediments methane production occurred only at depths where sulfate reduction was limited by a depleted supply of available sulfate. Winfrey and Zeikus (26) showed that sulfate additions to freshwater sediment inhibited methanogenesis and hypothesized that this was possibly due to competition between the sulfatereducing and methanogenic bacteria for a common substrate. Laboratory studies by Abram and Nedwell (2, 3) confirmed that methanogens were outcompeted by sulfate-reducing bacteria for the limited amount of hydrogen produced in sediments, and suggested that this competition was a possible explanation for the apparent inhibition of methanogenesis in the presence of sulfate reduction. The present work was undertaken to investigate in greater detail the relationship between sulfate reduction and methanogenesis in East Coast, United Kingdom, saltmarsh sediment.

Methanogenic community composition and anaerobic carbon turnover in submarine permafrost sediments of the Siberian Laptev Sea

“…If sulfate is present, sulfate reduction is the major catabolic process due to the higher affinity of sulfate reducers for hydrogen and acetate and a higher energy yield of sulfate reduction in comparison with methanogenesis (Winfrey and Zeikus, 1977;Schönheit et al, 1982;King, 1984). Under these conditions methanogenesis is very low (Franzmann et al, 1991;Senior et al, 1982) and only favoured if using competitive substrates like methanol or methylated amines (Oremland and Polcin, 1982;Ferdelman et al, 1997), as it is the case for Methanococcoides in this zone.…”

Comparison of microbial dynamics in marine and freshwater sediments: Contrasts in anaerobic carbon catabolism

“…However, recent evidence indicates that low but measurable rates of methane production do occur in sulfate-containing marine sediments which exhibit sulfate respiration (Table 2 ;Oremland 1975;Oremland and Taylor 1978;Warford et al 1979;Gunnarsson and Ronnow 1982;Kiene and Capone 1984). In most sediments containing > 1 mM SOh2-, methane production accounts for only a small percentage (CO. 1%) of anaerobic metabolism (Table 2; Winfrey and Ward 1983;Senior et al 1982). Most current estimates (Table 3; Jorgensen 1982;…”

Physiology and ecology of the sulphate‐reducing bacteria

“…Consequently, the in situ concentrations of these substrates are maintained at levels below those a t which methanogens can effectively compete (Lovley et al 1982). Low rates of methanogenesis can occur even in sulphate rich habitats (Senior et a!. 1982).…”