Functional organization outweighs spatial separation in structuring microbial communities across a...

Petroleum-hydrocarbon plumes in groundwater are shaped by hydrological transport, redox conditions, and indigenous microbial activity. However, it remains unclear whether spatial differences among groundwater microbiomes primarily reflect physical separation among wells or ecological reorganization associated with distinct attenuation states within a plume.

We integrated hydrogeological context, petroleum-hydrocarbon concentrations, hydrochemical variables, and shotgun-metagenomic profiles from 15 groundwater monitoring wells at a petroleum-hydrocarbon-impacted site. Community beta diversity, spatial and functional distance relationships, permutation-based group tests, and exploratory composite indices of natural attenuation potential and taxonomic-functional diversity were evaluated.

Genus-level community dissimilarity increased with estimated spatial distance (Mantel r = 0.240, p = 0.034), but was more strongly associated with functional-module dissimilarity (r = 0.670, p = 0.001). Biodegradation potential remained associated with community dissimilarity after controlling for spatial distance (partial Mantel r = 0.428, p = 0.001). Operational attenuation states explained 35.4% of genus-level compositional variation (PERMANOVA p = 0.008). High natural attenuation potential and high taxonomic-functional diversity occurred in partly distinct wells.

The results indicate that groundwater microbiome turnover within the plume is spatially structured but is more closely coupled to functional reorganization than to distance alone. Joint consideration of hydrological setting, microbial degradation potential, and functional diversity may improve groundwater natural-attenuation assessment.