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  • Articles  (77)
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  • 1
    Publication Date: 2015-07-08
    Description: Microbial methane oxidation rates in ocean and freshwater systems reveal how much of emitted methane from the sediments is oxidized to CO2 and how much can reach the atmosphere directly. The tracer-method using 3H-CH4 provides a way to measure MOX-rates even in water with low methane concentrations without needing any specific instrumentation. We assessed this method by implementing several experiments, collecting data from various environments, and including recent literature concerning the method to identify any uncertainties that should be considered. Our assessment reveals some difficulties of the method but also reassures previous assumptions to be correct. Some of the difficulties are hardly to be avoided, such as incubating all samples at the right in-situ temperature or limiting the variability of MOX-rate measurements in water of low methanotrophic activity. Other details, e.g. quickly measuring the total radioactivity after stopping the incubation, are easy to adapt in each laboratory. And yet other details as shaking during incubation and bottle size seem to be irrelevant. With our study we hope to improve and to encourage future measurements of MOX-rates in different environments and to provide a standard procedure of MOX measurements to make data of MOX better comparable.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 2
    Publication Date: 2015-09-23
    Description: Rivers represent a transition zone between terrestric and aquatic environments, as well as a transition zone between methane rich and methane poor environments. Methane concentrations in freshwater systems are in general higher than in marine systems. The Elbe River is one of the important rivers draining into the North Sea and with the Elbe river high amounts of methane are imported into the water column of the North Sea. The major biological sink is the oxidation of methane by aerobic methanotrophic bacteria. Eight cruises from November 2013 until November 2014 were conducted from Hamburg towards Helgoland. Methane oxidation rate was measured with radiotracers and methanotrophic abundance was assessed by q-PCR. Community fingerprinting was performed with monooxygenase intergenic spacer analysis (MISA). Combining all the data we could identify four environments (marine, coast, outer and inner estuary) with significantly different abundances. The marine environment had lowest abundances and highest abundances were found in the inner estuary. Comparison of the corresponding communities is in progress.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 3
    Publication Date: 2016-06-07
    Description: Large quantities of methane are stored in hydrates and permafrost within shallow marine sediments in the Arctic Ocean. These reservoirs are highly sensitive to climate warming, but the fate of methane released from sediments is uncertain. Here, we review the principal physical and biogeochemical processes that regulate methane fluxes across the seabed, the fate of this methane in the water column, and potential for its release to the atmosphere. We find that, at present, fluxes of dissolved methane are significantly moderated by anaerobic and aerobic oxidation of methane. If methane fluxes increase then a greater proportion of methane will be transported by advection or in the gas phase, which reduces the efficiency of the methanotrophic sink. Higher freshwater discharge to Arctic shelf seas may increase stratification and inhibit transfer of methane gas to surface waters, although there is some evidence that increased stratification may lead to warming of sub-pycnocline waters, increasing the potential for hydrate dissociation. Loss of sea-ice is likely to increase wind speeds and sea-air exchange of methane will consequently increase. Studies of the distribution and cycling of methane beneath and within sea ice are limited, but it seems likely that the sea-air methane flux is higher during melting in seasonally ice-covered regions. Our review reveals that increased observations around especially the anaerobic and aerobic oxidation of methane, bubble transport, and the effects of ice cover, are required to fully understand the linkages and feedback pathways between climate warming and release of methane from marine sediments.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 4
    Publication Date: 2016-10-13
    Description: Rivers represent a transition zone between terrestric and aquatic environments, and between methane rich and methane poor environments. The Elbe River is one of the most important rivers draining into the North Sea and, along with the Elbe, a potential importer of high amounts of methane into the water column of the North Sea. Twelve sampling cruises from October 2010 until June 2013 were conducted from Hamburg towards the mouth of the Elbe at Cuxhaven. The dynamic of methane concentration in the water column and its consumption via methane oxidation was measured. In addition, physico-chemical parameters were used to estimate their influence on the methanotrophic activity. We observed high methane concentrations at the stations in the area of Hamburg harbor (“inner estuary”) and about 10 times lower concentrations in the outer estuary (median of 416 versus 40 nmol/L, respectively). The methane oxidation (MOX) rate mirrored the methane distribution with high values in the inner estuary and low values in the outer estuary (median of 161 versus 10 nmol/L/d, respectively). Methane concentrations were significantly influenced by the river hydrology (falling water level) and the trophic state of the water (biological oxygen demand). In contrast to other studies no clear relation to the amount of suspended particulate matter (SPM) was found. Methane oxidation rates were significantly influenced by methane concentration and to a lesser extent by temperature. Methane oxidation accounted for 41 ± 12% of the total loss of methane in the summer/fall, but for only 5 ± 3% of the total loss in the winter/spring. We applied a modified box model taking into account the residence times of each water parcel depending on discharge and tidal impact. We observed almost stable methane concentrations in the outer estuary, despite a strong loss of methane through diffusion and oxidation. Thus, we postulate that the water column undergoes a balancing out in the outer Elbe estuary due to a strong additional input of methane, which could be provided by the extensive salt marshes near the river mouth.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 5
    Publication Date: 2017-06-20
    Description: Numerous articles have recently reported on gas seepage offshore Svalbard, because of gas emission that may be due to gas hydrate dissociation, possibly triggered by anthropogenic ocean warming. Here we report on findings for a much broader extent of seepage in water depths at and shallower than the gas hydrate stability zone. More than a thousand gas seepage sites imaged as acoustic flares generate a hundreds of kilometer-long plume. Most flares were detected in the vicinity of the Hornsund Fracture Zone. We postulate that the gas ascends from depth along the fracture zone; its discharge is focused on bathymetric highs and is constrained by glaciomarine and Holocene sediments in the troughs. A fraction of this dissolved methane (~1.8%) was oxidized whereas a minor but measureable fraction (0.05%) was transferred into the atmosphere in August 2015. The large scale seepage reported here is not linked to anthropogenic warming.
    Repository Name: EPIC Alfred Wegener Institut
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  • 6
    Publication Date: 2018-04-29
    Description: In intertidal areas, large amounts of organic matter in the form of kelp are regularly deposited on the beach. Mineralization of this organic matter leads to the release of many intermediates and end products into? the sediments. A wide variety of aerobic and anaerobic microorganisms control the mineralization process. The high input of reduced matter into the local ecosystem is apparent from elevated levels of sulfide and the abundance of white filamentous bacteria in the nearby surfaces? Or sediments?. The input of nutrients into this normally oligotrophic environment may subsequently also stimulate primary production of the microphytobenthos. We investigated the influence of kelp deposits on in situ concentrations of CO, H2, Fe(II), sulfide, CH4 and various nutrients on a beach on Helgoland. Our preliminary results show an enrichment of CO and H2 below kelp deposits. Exposure to O2 seemed essential for CO and H2 release during the process of kelp degradation, as was observed during incubation experiments. The most pronounced influence of kelp deposits was observed for Fe(II), with higher Fe(II) concentrations below kelp deposits, although large heterogeneity exists. Sulfide and CH4 were found in significant concentrations within sediments between kelp deposits and the adjacent sea. Remarkably, their levels were lower directly? below the kelp, whereas Fe(II) showed the opposite trend. We aim to define the processes responsible for the high sulfide and CH4 concentrations within the sediments, with a focus on the role of the high CO and H2 levels for sulfate reduction and methanogenesis. Through in situ measurements we will study the effects of variable oxygenation on the release of these compounds. We also aim to study and model the hydrology of the beach to assess the transport modes of the intermediates and nutrients through the permeable sands. We will furthermore determine the consequences of the nutrient input for the local microphytobenthos.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 7
    Publication Date: 2018-12-09
    Description: Permafrost thaw affects global climate, the land surface and coastal structures. Under subaquatic conditions, permafrost thaw is often more rapid than on land. The thaw depth below water bodies (taliks) and changes in biogeochemical gradients are difficult to predict. The influence of taliks and biogeochemical gradients on the production and release of the greenhouse gases methane and carbon dioxide is not clear yet. Although our research in this region has produced multi-decadal data sets, most of our knowledge on the methane cycle pertains only to the summer. We focus on water bodies in the Lena Delta region, including thermokarst ponds, lakes, lagoons and the marine shoreface. For most of the year, however, ice covers these water bodies, creating a barrier between the water column and the atmosphere, and changing benthic conditions. It is therefore important to assess methane-related processes during the ice-covered season. In spring 2017 we investigated the Lena Delta and Tiksi Bay at the end of winter, while still ice-covered. Thirty ice cores of different water bodies were obtained by Kovacs ice corer. The in situ temperature of the ice cores was measured immediately afterwards. Methane oxidation rates were determined with radio tracer method in melted ice core samples. Analyses of methane concentration and further hydrochemical analyses are on their way. Initial results indicate rather low activities of methane oxidation in the ice cores, but active biological processes in the water below.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 8
    Publication Date: 2019-01-29
    Description: We conducted multiple small (2011–2012) and one large sampling campaign (2013) at selected profiles along the Elbe River. With the data we were able to outline spatial and temporal variability of methane concentration, oxidation and emissions in one of the major rivers of Central Europe. The highest methane concentrations were found in human-altered riverine habitats, i.e., in a harbor (1,888 nmol L−1), in a lock and weirs (1409 ± 1545 nmol L−1), and in general in the whole “impounded” river segment (383 ± 215 nmol L−1). On the other hand, the lowest methane concentrations were found in the “lowland” river segment (86 ± 56 nmol L−1). The methane oxidation rate was more efficient in the “natural” segment (71 ± 113 nmol L−1day−1, which means a turnover time of 49 ± 83 day−1) than in the “lowland” segment (4 ± 3 nmol L−1day−1, which means a turnover time of 39 ± 45 day−1). Methane emissions from the surface water into the atmosphere ranged from 0.4 to 11.9 mg m−2 day−1 (mean 2.1 ± 0.6 mg m−2 day−1) with the highest CH4 emissions at the Meissen harbor (94 kg CH4 year−1). Such human-altered riverine habitats (i.e., harbors and similar) have not been taken into consideration in the CH4 budget before, despite them being part of the river ecosystems, they may be significant CH4 hot-spots. The total CH4 diffusive flux from the whole Elbe was estimated to be approximately 97 t CH4 year−1.
    Repository Name: EPIC Alfred Wegener Institut
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  • 9
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Most widely used medium for cultivation of methanotrophic bacteria from various environments is that proposed in 1970 by Whittenbury. In order to adapt and optimize medium for culturing of methanotrophs from freshwater sediment, media with varying concentrations of substrates, phosphate, nitrate, and other mineral salts were used to enumerate methanotrophs by the most probable number method. High concentrations (〉1 mM) of magnesium and sulfate, and high concentrations of nitrate (〉500 μM) significantly reduced the number of cultured methanotrophs, whereas phosphate in the range of 15–1500 μM had no influence. Also oxygen and carbon dioxide influenced the culturing efficiency, with an optimal mixing ratio of 17% O2 and 3% CO2; the mixing ratio of methane (6–32%) had no effect. A clone library of pmoA genes amplified by PCR from DNA extracted from sediment revealed the presence of both type I and type II methanotrophs. Nonetheless, the cultivation of methanotrophs, also with the improved medium, clearly favored growth of type II methanotrophs of the Methylosinus/Methylocystis group. Although significantly more methanotrophs could be cultured with the modified medium, their diversity did not mirror the diversity of methanotrophs in the sediment sample detected by molecular biology method.
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  • 10
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    Vereinigung für Angewandte und Allgemeine Mikrobiologie
    Publication Date: 2014-10-13
    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.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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