Underestimated environmental risks: Sediment stability weakening from accumulation of biomass in a eutrophic lake induced by microplastics

Sediments had emerged as a significant repository of MPs (microplastics) and biomass accumulation in eutrophic lakes, yet the mechanisms by which these particles impact sediment stability remained elusive. This study aimed to investigate the effect of MPs on the structural stability of sediments during the accumulation of biomass, as these properties could affect the formation of fluid sediment and trigger resuspension. A coaxial cylindrical rheometer was used to explore changes in the rheological properties of sediments under the influence of MPs. Within 30-day experiments, it was found that MPs could decrease sediment viscosity, yield stress, and flow point shear stress (τtau) by up to 61.2 %, 57.9 % and 54.3 %. In the early stage of the experiment, MP addition led to a significant decrease on sediment rheological properties, but then this effect decreased gradually. Subsequently, the variations in EPS (extracellular polymeric substances), organic matter, and microbial communities influenced by MPs were suggested to relate with the change in sediment rheology properties. These findings suggested that MPs could facilitate the degradation of biomass and decrease sediment rheological properties by altering sediment microbial activities. On this basis, the decline in sediment stability would increase the risk of sediment re-suspension under wind and wave disturbance. Overall, this study sheds light on the environmental challenges posed by MPs under biomass accumulation, offering a fresh perspective that deepens our comprehension of the environmental behavior of MPs in sediment ecosystems.