A greater understanding of the tightly linked trophic groups of anaerobic and aerobic bacteria residing in municipal solid waste landfills will increase our ability to control methane emissions and pollutant fate in these environments. To this end, we characterized the composition of methanogenic and methanotrophic bacteria in samples taken from two regions of a municipal solid waste landfill that varied in age. A method combining polymerase chain reaction amplification, restriction fragment length polymorphism analysis and phylogenetic analysis was used for this purpose. 16S rDNA sequence analysis revealed a rich assemblage of methanogens in both samples, including acetoclasts, H2/CO2-users and formate-users in the newer samples and H2/CO2-users and formate-users in the older samples, with closely related genera including Methanoculleus, Methanofollis, Methanosaeta and Methanosarcina. Fewer phylotypes of type 1 methanotrophs were observed relative to type 2 methanotrophs. Most type 1 sequences clustered within a clade related to Methylobacter, whereas type 2 sequences were broadly distributed among clades associated with Methylocystis and Methylosinus species. This genetic characterization tool promises rapid screening of landfill samples for genotypes and, therefore, degradation potentials.
The introduction of a deuterium-enriched tracer to benthic incubation chambers
emplaced on the sea floor of Port Phillip Bay provides a method of modelling
bio-irrigation within the sediments. Plots of deuterium
v. incubation time reveal that all seven chambers,
emplaced at four sites, indicate non-diffusive transport of pore-water solutes
across the sediment–water interface. Modelling indicates that advection
of overlying chamber water must occur to depths of 20–50 cm below the
interface and at rates between 150 and 700 mL h–1.
Multiple chambers deployed in the same region within the bay are consistent
with respect to bio-irrigation depth and rate. This indicates that the
distribution of infauna responsible for irrigation is quite consistent within
regions defined by sediment type and depth. However, various regions in the
bay show distinctly different irrigation rates; thus the distribution
and/or activity of infauna is not constant throughout the bay. At the
lower rate of pore-water advection, the entire water column in Port Phillip
Bay passes through the sediments within 200 days. Dissolved caesium, injected
into the chamber, is also an effective tracer of bio-irrigation although
adsorption onto sediment particles increases the uncertainty of model results.
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