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Institut für Wasser- und Umweltsystemmodellierung - IWS



"Microbial engineers in the aquatic sedimentary habitat (Abstract)"

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 presentation 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; one of the important ecosystem services of biofilm, called “biostabilization”. While this fascinating function has been recognized since long in the marine habitat (with a focus on microalgae and microphytobenthic mats), little is known from freshwaters. Generally, the interactions between biological growth and environmental abiotic parameters have been rarely addressed in a comprehensive manner. Here, we will firstly show that the bacterial stabilization capacity is much higher than previously thought but will concentrate then on results from naturally diverse freshwater biofilm; obtained within the ongoing DFG (Deutsche Forschungsgemeinschaft) project “Ecosystem Engineering: Sediment entrainment and flocculation mediated by microbial produced extracellular polymeric substances (EPS)”. We will provide key evidence of the significant stabilization potential of freshwater biofilm (increases up to 11 times as compared to controls) and its influence on the floc sizes, forms and settling velocity after entrainment to further impact sediment transport. Varying abiotic conditions proofed to have effects on the microbial stabilization potential: delayed development and stabilization under high flow velocities, while deploying highest adhesiveness and stability under good light conditions. Despite the important influence of light, the steepest increase in sediment stability happened in most of the experiments during the first 2 weeks. This was closely related to an increase in bacterial cell numbers, while the photoautotrophic microalgae developed mainly between week 3 and 5, giving evidence on the different successional stages of biofilm growth and their importance to functionality (here biostabilization). Thereby, changes in bacterial diversity, community dynamic and functional organization seem to be closely linked to the appearance (and types) of microalgae, unravelling simultaneously effects of competition and mutual dependence to impact EPS quantity and quality. The two main EPS components sugars and proteins were both significantly related to the increase in adhesiveness of the biofilm, sediment stability and floc formation; however we have evidence that the proteins might be the even better marker for biostabilization. We will briefly present the methods that are decisive to address biostabilization properly: the MagPI (Magnetic Particle Induction), straight erosion flumes (SETEG channel) and Gust Microcosm for floc erosion. KEYWORDS: biostabilization, adhesion, sediment stability, flocculation, microbial ecology, diatoms, bacteria