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Institut für Wasser- und Umweltsystemmodellierung - IWS



"Microbial Engineers in Aquatic Benthic Habitats "

The ETDC (Erosion, Transport, Deposition, Consolidation) cycle of sediments is crucial for the ecological and commercial health of aquatic habitats. It is now commonly accepted that the organisms inhabiting natural sediments mediate their erosive response. This paper addresses microbial colonization and secretion of EPS (extracellular polymeric substances) to influence the stability of the sediment bed and the characteristics of the eroded sediment flocs.

Natural assemblages of bacteria and diatoms were incubated on non-cohesive substratum (glass beads). Over time, microbial biomass and community composition (flow cytometry, microscopy, in situ fluorescence hybridization FISH) as well as secreted EPS contents (colloidal carbohydrates and proteins [mg g-1 sediment]) were monitored and related to sediment stability / adhesion (Cohesive Strength Meter, Magnetic Particle Induction). The eroded flocs were investigated for size, form, strength, and settling velocity.

Microbial colonization resulted in significant substratum stabilisation as compared to the controls (up to a factor of 12). Mixed assemblages had the highest stabilisation effect under conditions of natural relevance, but in response to varying abiotic conditions (e.g. nutrients), notable shifts in the populations affected the secretion of EPS and thus, biostabilisation. The floc characteristics of the eroded substratum showed distinct differences in their characteristics depending on the biological origin.

Microbial engineering is more important for mediation of sediment stability and transport than previously thought. Knowledge on this important ecosystem function needs to be incorporated in sediment transport models and has wide implications for water frame directive and sediment/pollutant management strategies.