Form, function and physics: The ecology of biogenic stabilization

The effect of biological cohesion on the behaviour of sediments is gaining increasing notice. This is partly supported by ecological theory in terms of the role of organisms as “ecosystem engineers” and the associated discussion of “niche construction”, suggesting an evolutionary role for habitat modification by biological action. In addition there is a strong societal and policy drive toward the “ecosystem approach” supporting an integrated examination of the functional roles of biota in selected habitats. In this context the increasing recognition of the importance of biological activity in the mediation the erosion, transport, deposition and consolidation (ETDC) cycle of sediments is important and advances in technology will improve our ability to examine these effect under their natural settings. This will shortly be combined with vastly enhanced molecular tools that will allowthe discrimination of microbial biodiversity and examination of their metabolism contribution to ecosystem function. This may lead to a step-change in our ability to research the influence of microbiota on natural sediment dynamics and opens an exciting era for new interdisciplinary research

Surface adhesion measurements in aquatic biofilms using magnetic particle induction: MagPI

Natural sediment stability is a product of interacting physical and biological factors, and whereas stability can be measured, few techniques allow sensitive assessment of the sediment surface as conditions change. For example, stability gradually increases as a biofilm develops or as salinity rises, or it might be influenced by toxic compounds. This article introduces a new technique (magnetic particle induction: MagPI) based on the magnetic attraction of specially produced fluorescent ferrous particles. The test particles are added to a surface and subjected to an incrementally increasing magnetic field produced by permanent magnets or electromagnets. There is a strong correlation between magnetic flux density (mTesla) and distance from the surface (r(2) = 0.99) for permanent magnets and between magnetic flux density and the current supplied to an electromagnet (r(2) &gt; 0.95). The magnetic force at which the particles are recaptured is determined as a measure of surface adhesion. MagPI therefore determines the "stickiness" of the surface, whether a biofilm, sediment, or other material. The average magnetic flux density required to remove test particles from diatom biofilms (15.5 mTesla) was significantly greater than from cyanobacterial biofilms (10 mTesla). Controls of fine glass beads showed little adhesion (2.2 mTesla). Surface adhesion is an important bed property reflecting the sediment system's potential to capture and retain new particles and accumulate material. MagPI offers a straightforward and economic way to determine the surface adhesion of a variety of surfaces rapidly and with precision. The technique may have applications in physical, environmental, and biomedical research.</p

Surface adhesion measurements in aquatic biofilms using magnetic particle induction: MagPI

Natural sediment stability is a product of interacting physical and biological factors, and whereas stability can be measured, few techniques allow sensitive assessment of the sediment surface as conditions change. For example, stability gradually increases as a biofilm develops or as salinity rises, or it might be influenced by toxic compounds. This article introduces a new technique (magnetic particle induction: MagPI) based on the magnetic attraction of specially produced fluorescent ferrous particles. The test particles are added to a surface and subjected to an incrementally increasing magnetic field produced by permanent magnets or electromagnets. There is a strong correlation between magnetic flux density (mTesla) and distance from the surface (r(2) = 0.99) for permanent magnets and between magnetic flux density and the current supplied to an electromagnet (r(2) &gt; 0.95). The magnetic force at which the particles are recaptured is determined as a measure of surface adhesion. MagPI therefore determines the "stickiness" of the surface, whether a biofilm, sediment, or other material. The average magnetic flux density required to remove test particles from diatom biofilms (15.5 mTesla) was significantly greater than from cyanobacterial biofilms (10 mTesla). Controls of fine glass beads showed little adhesion (2.2 mTesla). Surface adhesion is an important bed property reflecting the sediment system's potential to capture and retain new particles and accumulate material. MagPI offers a straightforward and economic way to determine the surface adhesion of a variety of surfaces rapidly and with precision. The technique may have applications in physical, environmental, and biomedical research.</p

Surface adhesion measurements in aquatic biofilms using magnetic particle induction: MagPI

Natural sediment stability is a product of interacting physical and biological factors, and whereas stability can be measured, few techniques allow sensitive assessment of the sediment surface as conditions change. For example, stability gradually increases as a biofilm develops or as salinity rises, or it might be influenced by toxic compounds. This article introduces a new technique (magnetic particle induction: MagPI) based on the magnetic attraction of specially produced fluorescent ferrous particles. The test particles are added to a surface and subjected to an incrementally increasing magnetic field produced by permanent magnets or electromagnets. There is a strong correlation between magnetic flux density (mTesla) and distance from the surface (r(2) = 0.99) for permanent magnets and between magnetic flux density and the current supplied to an electromagnet (r(2) &gt; 0.95). The magnetic force at which the particles are recaptured is determined as a measure of surface adhesion. MagPI therefore determines the "stickiness" of the surface, whether a biofilm, sediment, or other material. The average magnetic flux density required to remove test particles from diatom biofilms (15.5 mTesla) was significantly greater than from cyanobacterial biofilms (10 mTesla). Controls of fine glass beads showed little adhesion (2.2 mTesla). Surface adhesion is an important bed property reflecting the sediment system's potential to capture and retain new particles and accumulate material. MagPI offers a straightforward and economic way to determine the surface adhesion of a variety of surfaces rapidly and with precision. The technique may have applications in physical, environmental, and biomedical research.</p

Form, function and physics:the ecology of biogenic stabilisation

Purpose:  The objective of this work is to better understand the role that biological mediation plays in the behaviour of fine sediments. This research is supported by developments in ecological theory recognising organisms as “ecosystem engineers” and associated discussion of “niche construction”, suggesting an evolutionary role for habitat modification by biological action. In addition, there is acknowledgement from engineering disciplines that something is missing from fine sediment transport predictions.Materials and methods:  Advances in technology continue to improve our ability to examine the small-scale 2D processes with large-scale effects in natural environments. Advanced molecular tools can be combined with state-of-the-art field and laboratory techniques to allow the discrimination of microbial biodiversity and the examination of their metabolic contribution to ecosystem function. This in turn can be related to highly resolved measurements and visualisation of flow dynamics.Results and discussion:  Recent laboratory and field work have led to a paradigm shift whereby hydraulic research has to embrace biology and biogeochemistry to unravel the highly complex issues around on fine sediment dynamics. Examples are provided illustrating traditional and more recent approaches including using multiple stressors in fully factorial designs in both the laboratory and the field to highlight the complexity of the interaction between biology and sediment dynamics in time and space. The next phase is likely to rely on advances in molecular analysis, metagenomics and metabolomics, to assess the functional role of microbial assemblages in sediment behaviour, including the nature and rate of polymer production by bacteria, the mechanism of their influence on sediment behaviour.Conclusions:  To fully understand how aquatic habitats will adjust to environmental change and to support the provision of various ecosystem services, we require a holistic approach. We must consider all aspects that control the distribution of sediment and the erosion-transport-deposition-consolidation cycle including biological and chemical processes, not just the physical. In particular, the role of microbial assemblages is now recognised as a significant factor deserving greater attention across disciplines