Hydrological Impacts of the Surface Water Microbiome Structure and Predicted Metabolic Potential Adjacent to an Engineered Sanitary Landfill

Landfill leachate is a persistent environmental stressor, yet this study shows that seasonal hydrology and stormwater runoff, rather than leachate intrusion, primarily govern surface water chemistry and microbial community organization near engineered landfill systems in Malaysia. Multivariate analyses revealed seasonal variability in physicochemical parameters, while conservative tracer ratios and clay liner performance confirmed the absence of leachate ingress, underscoring containment effectiveness. Hydrological variability exerted primary control over microbial assemblages. 16S rRNA sequencing and PICRUSt2 inference indicated reduced α-diversity under dry-season low-flow conditions, with β-diversity analyses showing no significant seasonal separation (p > 0.05). Ternary compositional analysis revealed enhanced richness and compositional balance during the rainy season, attributable to increased hydrological mixing and dispersal. Dry-season assemblages exhibited dominance structures and enrichment of stress-adapted lineages. Phylum-level restructuring reflected seasonal gradients: Pseudomonadota and Bacteroidota prevailed during the rainy season, while Actinobacteriota and Bacillota dominated under ionic stress and reduced dilution. The persistence of core genera across seasons highlights microbial resilience and functional adaptability within dynamic biogeochemical interfaces. These results indicate that stormwater runoff, not landfill-derived leachate, drives observed microbial and hydrochemical dynamics. Findings are broadly applicable to regions with seasonal precipitation and expanding impermeable surfaces, informing global landfill performance assessments, monitoring strategies, and risk communication.