A multi-disciplinarily designed mesocosm to address the complex flow-sediment-ecology tripartite relationship on the microscale

Background: The stabilization of fine sediments via biofilms (‘biostabilization’) has various economic and ecological implications but is presently unaddressed within lotic waters. To investigate natural biofilm growth and functionality in freshwater sediments under controlled boundary conditions, a unique mesocosm was constructed that combines established know-how from engineering and natural sciences and consists of six straight flumes. To test the comparability of biofilm growth within one flume and between the flumes, extracellular polymeric substances (EPSs), microbial biomass and microbial community composition were closely monitored over time and space as well as in relation to biofilm adhesiveness (proxy for biostabilization). Results: Most importantly, biofilm development and biostabilization capacity revealed no significant differences within flume regions or between the flumes and the biofilms significantly stabilized the substratum as compared to abiotic controls. However, interesting temporal successions in biofilm growth phases became visible in shifting abundance and diversity of bacteria and microalgae resulting in varying EPS secretion and biostabilization. Conclusions: These findings demonstrated the importance of biostabilization for fine sediment dynamics in freshwaters. Secondly, this unique setup allows comparable biofilm growth under controlled environmental conditions, an important requisite for future research on the ecological significance and impact of biostabilization for ecosystem functioning at varying environmental scenarios.