Effect of surface biofilm on sediment transport implemented in a 1D model

Abstract:

Shallow tidal environments are very productive ecosystems and they are sensitive to environmental changes and sea level rise. The study of the bio-morphodynamic evolution of these environments is therefore a crucial task as the effect of small-scale biological activity on large-scale cohesive sediment dynamic like tidal basins and estuaries is still largely unquantified. Biological activity on the bottom of the seabed is known to have significant influence on the dynamic of cohesive sediment on a small spatial and on temporal scale and bed composition. Bed stabilization is induced by secretion of extracellular polymeric substances (EPS) by movement of microphytobenthos and the presence of biofilm. The aim of this study is to incorporate relevant biological processes with physical processes to assess the influence of biology on cohesive sediment transport and distribution, assuming a linear relation between biofilm biomass and sediment stabilization. A simplified model for the growth of benthic biofilm subject to variable hydrodynamic disturbances and a biofilm-dependent erodibility (biostabilization) is implemented in a 1D morphodynamic model of tide-dominated channels transporting nonuniform sand and interacting with the ocean. The effect of temperature and seasonality on the development of biofilm is investigated. Preliminary results show that the presence of the biofilm increases the time for the bed to reach morphological equilibrium and modifies the final distribution of the sediment in the deposit. Bio-stabilized bed has a deposit that is finer than the case without biofilm. As the temperature increases from the optimum temperature for the growth of biofilm, the bed becomes more mobile.