Biogeochemical controls on soil dispersion and bank stability in the unvegetated, meandering Sulengguole River, Qaidam Basin, China

Abstract

Unvegetated meandering rivers play a pivotal role in sediment transport and landscape evolution within dryland environments, yet the interplay between abiotic and biotic factors that govern channel bank stability and migration remains poorly understood. While sedimentological processes have been extensively studied, the combined influence of sediment geochemistry and microbial activity on erosion and bank dynamics remains poorly understood. We investigate a single, nearly unvegetated bend in the Sulengguole River, Qaidam Basin, China, using remote sensing, field observations, and laboratory analyses (grain-size distribution, salinity, ion profiling, and 16S rRNA sequencing) to elucidate how sedimentology, geochemistry, and microbial diversity drive bank erosion and meander migration under uniform seasonal and climatic conditions. Field sampling focused on cavity-rich and compact sediment layers along a representative meander bend. Analyses of grain-size distribution, salinity, ion concentrations, and microbial diversity (via 16S rRNA sequencing) revealed significant spatial and compositional differences in bank stability. Mud-dominated banks, undermined by cavity formation, were found to migrate more than four times faster than interbedded sand-mud banks, as shown by satellite imagery and sedimentological data. High salinity and ion concentrations in finer sediments at elevated bank zones were strongly associated with increased soil dispersion and enhanced erosion. Microbial diversity analysis further indicated that cavity-rich layers were dominated by Brevibacterium and Pseudomonas, taxa known to promote bioerosion, whereas cavity-free layers, enriched with Acinetobacter and Brevundimonas, contributed to sediment cohesion. These findings highlight the critical role of abiotic-biotic interactions in influencing bank stability, sediment transport, and channel migration in unvegetated river systems. By demonstrating how geochemical and biological factors interact to shape riverbank erosion and morphodynamics, this study provides new insights into sediment dynamics in dryland rivers. The results have broader implications for understanding sediment transport in meandering river systems, as well as in interpreting landscape evolution in ancient fluvial records and extraterrestrial environments.