Sulfide fluxes in a microbial mat from the Ebro Delta, Spain.

The sulfur cycle of Ebro Delta microbial mats was studied in order to determine sulfide production and sulfide consumption. Vertical distribution of two major functional groups involved in the sulfur cycle, anoxygenic phototrophic bacteria and dissimilatory sulfate-reducing bacteria (SRB), was also studied. The former reached up to 2.2x10(8) cfu cm(-3) sediment in the purple layer, and the latter reached about 1.8x10(5) SRB cm(-3) sediment in the black layer. From the changes in sulfide concentrations under light-dark cycles it can be inferred that the rate of H(2)S production was 6.2 micro mol H(2)S cm(-3) day(-1) at 2.6 mm, and 7.6 micro mol H(2)S cm(-3) day(-1) at 6 mm. Furthermore, sulfide consumption was also assessed, determining rates of 0.04, 0.13 and 0.005 mmol l(-1) of sulfide oxidized at depths of 2.6, 3 and 6 mm, respectively.