ALBERT

Description: Rivers represent a transition zone between terrestrial and aquatic environments, as well as a transition zone between methane rich and methane poor environments. Methane concentrations are generally higher in freshwater systems than in marine systems. The Elbe River is one of the crucial drainages into the North Sea and by this high amounts of methane are imported into the marine water column. Oxidation of methane by aerobic methanotrophic bacteria is the major biological sink. Six cruises from November 2013 until June 2014 were conducted along the salinity gradient from Hamburg towards Helgoland. Methane oxidation rate was measured with radiotracers and the abundance of methanotrophic bacteria was assessed via real-time PCR. A newly designed primer targeting the genomic sequence encoding the α-subunit of the functional pMMO enzyme in water column organisms was amplified and tested against the conventional primer set. At the marine stations the cell number was relatively stable with 3 x 104 cells per L, while in the Elbe cell numbers ranged between 103 – 106 cells per L. Environmental parameters (temperature, salinity, SPM) seemed to have no influence on the abundance. However the interaction between activity and abundance seemed to be more complex.

Description: ABSTRACT: Salinity is an important environmental control of aerobic methane oxidation, which reduces the emission of the potent greenhouse gas methane into the atmosphere. The effect of salinity on methane oxidation is especially severe in river estuaries and adjacent coastal waters, which are important sources of methane emission and, at the same time, are usually characterized by pronounced salinity gradients. Using methane oxidation rates determined by a radiotracer technique as a measure of methanotrophic activity, we tested the effect of immediate and gradual salinity changes on pure cultures of methanotrophic bacteria, and natural freshwater (Elbe River) and natural marine (North Sea) methanotrophic populations. According to our results, Methylomonas sp. and Methylosinus trichosporium are resistant to an increase in salinity, whereas Methylovulum sp. and Methylobacter luteus are sensitive to such an increase. Natural methanotrophic populations from freshwater are more resistant to an increase in salinity than those from marine water are to a decrease in salinity. In contrast to an immediate change of salinity, gradual change (1.25 PSU d−1) can attenuate salinity stress. Experiments with the natural populations revealed different reactions to changes in salinity; thus, we assume that the initial composition of the methanotrophic population, i.e. the ratio of sensitive versus resistant strains, also governs the community response to salinity stress.Repeated experiments with the natural populations revealed different reactions to changes of salinity; thus we assume that the initial composition of the methanotrophic population, i.e. the ratio of sensitive and resistant strains, also governs the community response to salinity stress.

Description: Shelf sea areas are the primary oceanic source for methane release, the most abundant hydrocarbon in the atmosphere. As such, the southern North Sea’s methane concentration is mainly determined by river runoff and tidal marshes. Within such a highly variable temperate estuary, this study is the first to reveal detailed information on the in situ activity, abundance and community structure of methane oxidizing bacteria along a transect from the marine environment near Helgoland island to the riverine harbor of Hamburg, Germany. The in situ methane oxidation rate was determined with a radio tracer, and methane concentration with the head-space method. Abundance and diversity of the methanotrophic bacterial community in the water column was assessed with quantitative polymerase chain reaction for the particulate methane monooxygenase and monooxygenase intergenic spacer analysis. Median abundances ranged from 2.8 × 104 cells l−1 in the marine environment to 7.5 × 105 cells l−1 in the riverine environment. Except for salinity, no conclusive linear correlation between any environmental parameter and the abundance of methanotrophs could be determined. Relating activity with abundance of methanotrophs showed that about 70% of the population is inactive, especially in the coastal and marine environment. This study found distinct operational taxonomic unit (OTU) community compositions among the 3 environmental categories (river, coast, marine). Several identified OTUs have been reported previously and imply a wide geographic occurrence. Overall, we propose that salinity is the most important driver of differing communities in the riverine, coastal and marine environment.