Process measurement and phylogenetic analysis of the sulfate reducing bacterial communities of two contrasting benthic sites in the upper estuary of the Great Ouse, Norfolk, UK

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Abstract
Seasonal measurements of sedimentary sulfate reduction at a freshwater site (site 1) and a brackish/marine site (site 4) in the upper estuary of the Great Ouse, Norfolk, UK revealed very similar integrated annual rates of sulfate reduction: 5.3 and 3.7 mol sulfate m−2 year−1, respectively, but two distinctly different seasonal cycles. At site 4 sulfate reduction followed a seasonal pattern with summer maxima and winter minima, suggesting temperature dependence, but in contrast at site 1 there was no distinct seasonal cycle. Use of 16S rRNA-targeted oligonucleotide probes to investigate the active sulfate reducing bacterial (SRB) populations suggested that populations of SRB remained relatively constant at site 4 throughout the year. However, at site 1 distinct peaks in signal from a Desulfovibrio spp.-targeted probe were measured which corresponded with peaks in sulfate reduction activity. In addition, sedimentary profiles suggested that both sulfate reduction activity and active SRB populations peaked at 0–5 cm into the sediment at site 1 but deeper into the sediment at 9–10 cm at site 4. The results indicate that SRB population dynamics are more complex than process measurements would suggest.

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