Coupling of biomass production and sedimentation of suspended sediments in eutrophic rivers

In eutrophic rivers, not only the hydraulic processes (e.g. turbulent flow, deposition, resuspension) but also the biological ones (e.g. primary production, metabolic losses, grazing, decomposition and agglomeration) show a great influence on the dynamics of the total suspended sediments. On the other hand, because of the light limitation, the primary production itself is strongly dependent on the actual suspended matter concentration. In the present paper, model approaches to the biological and hydraulic coupling are assessed and discussed in comparison with measuring data. The coupling approaches have been developed and fixed in the model system pamir-c, which combines both the hydrobiological and the hydraulic effects by means of coupled algebraic and differential equations. We used pamir-c to simulate the concentration development over 3 years in a well-examined compartment of the Spree River near Berlin, Germany. The simulation runs show, that the primary production as well as the hydraulic regime have a great influence on the mean particle properties, and thereby on the mean settling velocity of the suspended particles. Moreover, they both regulate the existence and availability of resuspendible sediments in the river bed. So, via the deposition and resuspension of sediments, both the hydraulic and hydrobiological effects proved to be highly relevant for the concentration development in eutrophic rivers.