Microbial consortia in wetland sediments: A biomarker analysis of the effects of hydrological regime, vegetation and season on benthic microbes

Microbial consortia in the sediments from a permanent wetland near Albury-Wodonga in north-eastern Victoria, Australia (Ryans 1 Billabong), and an ephemeral wetland near Shepparton in central Victoria (Raftery's Swamp) were quantified by analyses of phospholipid fatty acid (PLFA), polar lipid ether lipid (PLEL), sterol and alcohol profiles. Prokaryotic organisms dominated the benthic assemblages in both wetlands. Total prokaryotic abundance (i.e. eubacteria plus archaea) was estimated to be (7-17) x 10⁹ cells g^-1 sediment (dry weight). Methanogenic archaea were estimated to number (1-5.4) x 10⁹ cells g^-1 and to account for 11-36% of the total benthic prokaryotes; these values are apparently among the highest recorded for temperate lake or river environments. PLFAs indicative of specific metabolic groups (e.g. sulfate-reducing bacteria (SRB), methanotrophic bacteria, etc.) were also detected. The PLFA profiles indicated that Type I methanotrophs (abundant in C₁₆ PLFAs) were more abundant than the Type II group, which contain C₁₈ PLFAs. Acetate-utilizing SRB were more abundant than were lactate-utilizing SRB, but neither group was dominant. Ergosterol was not detected, which suggested that fungi were not a significant component of the benthic microbial consortia in spite of both wetlands having abundant inputs from aquatic and fringing vascular plants. Other biomarkers, such as sterols, long-chain alcohols, triterpenoids and phytol, demonstrated inputs from these higher plants. PLFA, PLEL and sterol profiles indicated that benthic microbial consortia were affected by hydrological regime, the presence of aquatic vegetation, and season. Information from this preliminary study may assist in the making of informed management decisions on environmental water allocations for natural ecosystems.