Decoupling of Biodiversity and Network Stability in Sediment-Laden Rivers: A Cross-Regional Analysis of Multitrophic Communities in the Yellow River

Hydro-sedimentary conditions regulate resource availability and habitat heterogeneity in rivers, representing a key constraint on multitrophic communities. However, the mechanisms by which these conditions shape multitrophic assemblages and mediate their environmental responses remain underexplored. Here, we investigated multitrophic communities along the Yellow River, categorizing sampling sites into reservoir (RAG), low-sediment (LSG), and high-sediment (HSG) regions based on the habitat type and a suspended sediment threshold of 0.15 mg L^-1. Basin-wide surveys across two seasons revealed that multitrophic species richness followed the pattern of RAG < LSG < HSG, whereas protozoan and metazoan evenness markedly declined in HSG. Among α-diversity metrics, species richness was best explained by physicochemical and hydrological variables (35.4-94.2%), suggesting its highest sensitivity to environmental filtering. The suspended sediment exhibited a threshold effect on algal and protozoan diversity, enhancing species richness at low concentrations but suppressing it at higher levels. Network analyses revealed higher multitrophic network complexity in LSG and HSG than in RAG, but cross-trophic networks in HSG exhibited the lowest robustness and fewest keystone taxa. Notably, nutrients destabilized the RAG network via diversity-mediated pathways, while intensive land use in HSG impaired stability by altering network complexity. These findings provide mechanistic insights into biodiversity dynamics in sediment-laden rivers and underscore the need to incorporate sediment dynamics into riverine biodiversity conservation frameworks.