MCH11_12
Linking Molecular Microbial Ecology to Geochemistry in a Coastal Hypoxic Zone
Microbial ecology of the sediments within the western hypoxic zone of the Gulf of Mexico
Multiple environmental mechanisms have been proposed to control bottom water hypoxia (< 2 mg O2 L-1) in the northern Gulf of Mexico Louisiana shelf. Near-bottom hypoxia has been attributed to a direct consumption of oxygen through benthic microbial respiration and a secondary chemical reaction between oxygen and reduced metabolites (i.e. ferrous iron and total sulfide) from these populations. No studies to date have examined the metabolically active microbial community structure in conjunction with the geochemical profile in these sediments. Temporal and spatial differences in dissolved and solid phase geochemistry were investigated in the upper 20 cm of the sediment column. Pyrosequencing of reverse transcribed small subunit (SSU) ribosomal ribonucleic acid (rRNA) was used to determine population distribution. Results indicated that populations shallower than 10 cm below surface were temporally variable yet uniform between sites, while below this depth, populations were more site specific. This suggests a shallow interaction potential between the water column and the benthic microbial population. The presence of dissolved reduced iron in the upper sediment column was indicative of low oxygen concentration, yet sulfide was at or below detection limits. Sulfate and iron reducing and oxidizing populations were metabolically active at similar depths suggesting potential recycling of products. General metabolic activity may be limited by low carbon concentrations, reducing the potential for microbial respiration.