PROCESS MEASUREMENT AND PHYLOGENETIC ANALYSIS OF THE SULFATE-REDUCINGBACTERIAL COMMUNITIES OF 2 CONTRASTING BENTHIC SITES IN THE UPPER ESTUARY OF THE GREAT OUSE, NORFOLK, UK

Seasonal measurements of sedimentary sulfate reduction at a freshwater site (site 1) and a brackish/marine site (site 4) in the upper estuar y of the Great Ouse, Norfolk, UK revealed very similar integrated annu al 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 s ite 1 there was no distinct seasonal cycle. Use of 16S rRNA-targeted o ligonucleotide probes to investigate the active sulfate reducing bacte rial (SRB) populations suggested that populations of SRB remained rela tively constant at site 4 throughout the year. However, at site 1 dist inct peaks in signal from a Desulfovibrio spp.-targeted probe were mea sured which corresponded with peaks in sulfate reduction activity. In addition, sedimentary profiles suggested that both sulfate reduction a ctivity 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 resul ts indicate that SRB population dynamics are more complex than process measurements would suggest.