Spatiotemporal variations in LNAPL infiltration in the vadose zone microbial community metabolism and coupled...

Light nonaqueous phase liquids (LNAPLs) contamination poses a persistent threat to soil and groundwater systems. As the interface between the land surface and aquifers, the vadose zone controls contaminant transportation. We systematically investigated LNAPL migration and attenuation in the vadose zone across temporal and spatial scales, elucidated the metabolic profile and composition of the microbial community, and revealed coupled abiotic-biotic mechanisms. The results revealed that LNAPL infiltration in the vadose zone varies across temporal and spatial scales. Over time, microbial diversity and richness decreased as the number of differentially abundant metabolites decreased from 28 at A2 (22 days after LNAPL release) to 17 at A3 (64 days after LNAPL release). Within the plume, dominant hydrocarbon degraders, specifically Proteobacteria and Pseudomonas, progressively accumulated in the residual water zone (RWZ) and horizontal migration zone (HMZ). The significant spatiotemporal distribution of petroleum-degrading microbial communities is collectively driven by variations in LNAPL infiltration and environmental factors. Moreover, infiltrated LNAPLs, in the presence of O₂/H₂O and active microbes, are transformed into LNAPL metabolites accompanied by H⁺ generation, which further leads to a decrease in the LNAPL concentration, environmental pH, ORP, and θ. This process establishes a biotic-abiotic coupling mechanism among LNAPLs, environmental factors, and microorganisms, which jointly drives the migration and distribution of LNAPLs in the vadose zone. This work presents a novel, systematic elucidation of the spatiotemporal mechanisms by which microbial degradation governs LNAPL migration and attenuation, providing a reference for understanding the natural attenuation mechanisms of LNAPL in the vadose zone and for optimizing subsequent remediation strategies.