Structural stability of Marshland soils of the riparian zone of the Tidal Elbe River

Dredging and regulation of the Elbe federal waterway are leading to a modification of hydromorphological characteristics, and they are potentially affecting the riparian zone of the Tidal Elbe estuary. Accumulation and erosion areas are shifted and altered. Due to a natural salinity gradient, soil (micro)mechanical stability is mainly influenced by texture, water content, matric potential (pre-desiccation), ionic strength (Na+, Ca2+, Mg2+, Cl−, CO32−, SO42−), osmotic pressure, and organic matter. Zetapotentials (ζ) were derived from particle charge density (PCD) measurements; due to this, particle strength (attractive vs. repulsive forces) on the colloidal scale was determined. Rheometry was used to determine micromechanical parameters (particle-to-particle-scale), i.e., storage and loss moduli G′ and G″ (Pa), loss factor tan δ (G″/G′) integral z (dimensionless parameter of quasi-elasticity), and to characterize the shear behaviour. Dynamic loading tests were performed to determine mechanical strength and precompression stress on the meso scale (236 cm3 structured soil cores). Collected data derived from this approach deliver important information to classify and estimate the mechanical stability of the riparian zone of the Tidal Elbe estuary on several scales. With increasing salt content, dispersing effects due to repulsive forces of Na+ were observed, as well as strengthening effects due to attractive forces of Ca2+. Hence, Salinic Tidalic Fluvisols are prone to erodibility, if compared to well-structured, matured Calcaric Fluvisols or Fluvi-Calcic Gleysols. Susceptibility to erosion increased with increasing sodium saturation.