Soil–water characteristic curves of extracellular polymeric substances-affected soils and sensitivity analyses of correlated parameters

Quantifying the ways in which biological activity may alter the hydraulic properties of soils (the soil-water characteristic curves; SWCCs) is vital for understanding and engineering water pollution and supply systems. The study used centrifugation and a sand funnel method to determine the SWCCs of pure sandy soils with different particle sizes and sandy soils mixed with different extracellular polymeric substance (EPS) analogs. The sensitivity of correlated parameters for SWCCs obtained using a van Genuchten (VG) model was analyzed by single-factor perturbation analysis. The results show the following. (1) Fine sand has the strongest water retention ability. (2) The more polysaccharide there is in the media, the stronger its water-holding capacity. Polysaccharide not only has its strong water-holding capacity, but also changes the structure of medium to increase water-holding capacity. The humic acid and protein components had little effect on the hydrodynamic properties of fine sandy soil. (3) Sensitivity analyses revealed that the saturated water content, θs, greatly affected the ability of solute transport to reach equilibrium concentrations. Therefore, it is essential to define the range of media particles and component content, and ensure the accuracy of VG model parameters in the practical application of soil media affected by biological activity.