Exopolysaccharides from Rhizobium Tropici modified the surface characteristics of a Mississippi River Levee soil clay and its bulk soil properties

Global climate change has led to the increased frequency of extreme flooding events and heightened the vulnerability of river levees to flood related damage. One promising approach to enhancing the sustainability of levee stabilization is the use of eco-friendly, biologically produced soil additives as alternatives to conventional materials for erosion control. This study investigates the effects of exopolysaccharides (EPS) produced by Rhizobium tropici on the physical and engineering properties of clayey soil from a Mississippi River levee. Specifically, the study examines how EPS affects particle size, surface charge, surface area, and key bulk soil properties, including Atterberg limits, compaction behavior, and hydraulic conductivity. Soil samples were collected from a levee embankment located in south of Vidalia LA, an area historically prone to slough slides due to highly plastic nature of its floodplain clay soils. X-ray Power Diffraction was used to characterize the mineralogy of soil clay, EPS and EPS-clay composites. Particle size distribution and Zeta potentials measurements were performed on EPS and EPS-amended clays. Engineering test included Atterberg limit determinations (liquid and plastic limits) and standard compaction tests. The addition of EPS significantly increased the aggregate particle sizes of the levee clay through formation of EPS-clay composites. A strong correlation was observed between mean particle sizes and zeta potential in the composites. EPS also increased the liquid limit and plasticity of the soil while significantly reducing its hydraulic conductivity. Overall, EPS-amended soil demonstrated improved resistance to seepage and erosion, indicating that EPS has the potential to enhance levee soil stability and contribute to more sustainable flood control infrastructure.