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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 43 (1994), S. 1131-1138 
    ISSN: 0006-3592
    Keywords: confocal microscopy ; microelectrodes ; cell clusters ; pores ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Aerobic biofilms were found to have a complex structure consisting of microbial cell clusters (discrete aggregates of densely packed cells) and interstitial voids. The oxygen distribution was strongly correlated with these strutures. The voids facilitated oxygen transport from the bulk liquid through the biofilm, supplying approximately 50% of the total oxygen consumed by the cells. The mass transport rate from the bulk liquid is influenced by the biofilm structure; the observed exchange surface of the biofilm is twice that calculated for a simple planar geometry. The oxygen diffusion occurred in the direction normal to the cluster surfaces, the horizontal and vertical components of the oxygen gradients were of equal importance. Consequently, for calculations of mass transfer rates a three-dimensional model is necessary. These findings imply that to accurately describe biofilm activity, the relation between the arrangement of structural components and mass transfer must be undrstood. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 44 (1994), S. 636-641 
    ISSN: 0006-3592
    Keywords: biofilm ; hydrodynamics ; mass transport ; particle tracking ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Liquid flow was studied in aerobic biofilms, consisting of microbial cell clusters (discrete aggregates of densely packed cells) and interstitial voids. Fluorescein microinjection was used as a qualitative technique to determine the presence of flow in cell clusters and voids. Flow velocity profiles were determined by tracking fluorescent latex spheres using confocal microscopy. Liquid was flowing through the voids and was stagnant in the cell clusters. Consequently, in voids both diffusion and convection may contribute to mass transfer, whereas in cell clusters diffusion is the dominant factor. The flow velocity in the biofilm depended on the average flow velocity of the bulk liquid. The velocity profiles in biofilms were linear and the velocity was zero at the substratum surface. The velocity gradients within biofilms were 50% of that near walls without biofilm coverage. The influence of the biofilm roughness on the flow velocity profiles was similar to that caused by rigid roughness elements. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2020-03-12
    Description: We report primary production and respiration of Posidonia oceanica meadows determined with the non-invasive aquatic eddy covariance technique. Oxygen fluxes were measured in late spring at an open-water meadow (300 m from shore), at a nearshore meadow (60 m from shore), and at an adjacent sand bed. Despite the oligotrophic environment, the meadows were highly productive and highly autotrophic. Net ecosystem production (54 to 119 mmol m-2 d-1) was about one-half of gross primary production. In adjacent sands, net primary production was a tenth- to a twentieth smaller (4.6 mmol m-2 d-1). Thus, P. oceanica meadows are an oasis of productivity in unproductive surroundings. During the night, dissolved oxygen was depleted in the open-water meadow. This caused a hysteresis where oxygen production in the late afternoon was greater than in the morning at the same irradiance. Therefore, for accurate measurements of diel primary production and respiration in this system, oxygen must be measured within the canopy. Generally, these measurements demonstrate that P. oceanica meadows fix substantially more carbon than they respire. This supports the high rate of organic carbon accumulation and export for which the ecosystem is known.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
    Publication Date: 2021-01-25
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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  • 5
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    AMER SOC LIMNOLOGY OCEANOGRAPHY
    In:  EPIC3Limnology and Oceanography, AMER SOC LIMNOLOGY OCEANOGRAPHY, ISSN: 0024-3590
    Publication Date: 2020-09-07
    Description: We investigated the impact of kelp deposition on the geochemistry and microbial community composition of beach sands on the island of Helgoland (North Sea). The composition of the microbial community at a beach with regular kelp deposition appeared shaped by this regular input of organic material, as indicated by significantly higher proportions of aerobic degraders, fermenters, and sulfur cycling microorganisms. Rapid degradation of deposited kelp by this community leads to high levels of dissolved organic and inorganic carbon and nutrients, a lower pH and anoxia. Aerobic respiration, fermentation, Fe- and SO42- reduction and methanogenesis were strongly enhanced, with SO42- reduction being the main process in kelp degradation. SO42- reduction rates increased 20 to 25-fold upon addition of kelp. The main route of electrons from kelp to SO42- was not via CO and H2, as expected, but via organic fermentation products. O2 supply by the tides was not sufficient and reduced intermediates escaped from the sediment with tidal water retraction. The resulting extremely high levels of free sulfide (〉10 mmol L-1) lead to abundant filamentous growth of sulfur-oxidizing bacteria largely composed of a rare O2-adapted Sulfurovum lacking the expected denitrification genes. Our results show that regular kelp deposition strongly enhances the thermodynamic disequilibrium in the beach sand habitat, leading to a dramatic enhancement of the sulfur cycle.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 6
    Publication Date: 2021-12-15
    Description: We investigated the effect of an artificial CO2 vent (0.0015−0.037 mol s−1), simulating a leak from a reservoir for carbon capture and storage (CCS), on the sediment geochemistry. CO2 was injected 3 m deep into the seafloor at 120 m depth. With increasing mass flow an increasing number of vents were observed, distributed over an area of approximately 3 m. In situ profiling with microsensors for pH, T, O2 and ORP showed the geochemical effects are localized in a small area around the vents and highly variable. In measurements remote from the vent, the pH reached a value of 7.6 at a depth of 0.06 m. In a CO2 venting channel, pH reduced to below 5. Steep temperature profiles were indicative of a heat source inside the sediment. Elevated total alkalinity and Ca2+ levels showed calcite dissolution. Venting decreased sulfate reduction rates, but not aerobic respiration. A transport-reaction model confirmed that a large fraction of the injected CO2 is transported laterally into the sediment and that the reactions between CO2 and sediment generate enough heat to elevate the temperature significantly. A CO2 leak will have only local consequences for sediment biogeochemistry, and only a small fraction of the escaped CO2 will reach the sediment surface.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
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  • 7
    Publication Date: 2021-12-15
    Description: Carbon capture and storage (CCS) is a key technology to reduce carbon dioxide (CO2) emissions from industrial processes in a feasible, substantial, and timely manner. For geological CO2 storage to be safe, reliable, and accepted by society, robust strategies for CO2 leakage detection, quantification and management are crucial. The STEMM-CCS (Strategies for Environmental Monitoring of Marine Carbon Capture and Storage) project aimed to provide techniques and understanding to enable and inform cost-effective monitoring of CCS sites in the marine environment. A controlled CO2 release experiment was carried out in the central North Sea, designed to mimic an unintended emission of CO2 from a subsurface CO2 storage site to the seafloor. A total of 675 kg of CO2 were released into the shallow sediments (~3 m below seafloor), at flow rates between 6 and 143 kg/d. A combination of novel techniques, adapted versions of existing techniques, and well-proven standard techniques were used to detect, characterise and quantify gaseous and dissolved CO2 in the sediments and the overlying seawater. This paper provides an overview of this ambitious field experiment. We describe the preparatory work prior to the release experiment, the experimental layout and procedures, the methods tested, and summarise the main results and the lessons learnt.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
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  • 8
    Publication Date: 2021-10-20
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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