Modeling Biofilms Development with Hydraulic and Sediment Transport Processes in the Yangtze River

Sediment in a water column provides excellent substratum for microorganism colonization, and further contributes to the formation of biofilm, which is a complex structure consisting of living microorganisms and their metabolic products known as extracellular polymeric substances (EPS). Most natural sediment is invariably covered by biofilms in rivers and lakes, which alter the physical and chemical of sediment, resulting in substantial influence on sediment transport, and further affect natural river evolution, pollutant transport, and habitat changes. Moreover, the hydrodynamics and sediment transport processes also play a crucial role in the development of microbial biomasses by impacts on biofilms growth, which is essential for the substance circulation in aquatic ecosystems. In this study, the one-dimensional and three-dimensional model of hydrodynamics, sediment transport and biofilm development are presented for the middle and lower reaches of Yangtze River and Three Gorges Reservoir (TGR), respectively. The proposed three-dimensional model is applied to estimate the accumulation of biofilms in TGR with the main consideration of continuous sediment deposition process, while the one-dimensional model is used to predict the spatial and temporal distribution of microbial biomasses with the main consideration of the sediment erosion process in the middle and lower reaches of Yangtze River. Results show that the average annual accumulation of biofilms is about 9.4 kg/m² in TGR, and the biofilms decrease significantly in the middle and lower reaches of Yangtze River after the operation of TGR. The proposed model can reasonably reflect interrelation between biofilms development and the processes of hydraulic and sediment transport, which can be further applied to provide references for the integrated management of natural aqueous systems.