Decoupling petroleum-hydrocarbon burden from metagenomic degradation potentials identifies subsurface layers with...

Petroleum-hydrocarbon concentrations delineate contaminated soil but do not indicate whether contaminant burden is matched by indigenous degradation potential. We integrated total petroleum hydrocarbons (TPH) in the C10-C40 range with four process-specific metagenomic degradation potentials to identify subsurface layers where intrinsic bioremediation may be constrained. We collected 36 depth-resolved soil samples from six boreholes at a former refinery, including 22 with matched metagenomic profiles. CANT-HYD annotation identified 135 nonredundant genes across 15 hidden Markov models, representing aerobic and anaerobic degradation potentials for aromatic hydrocarbons and alkanes. TPH was positively associated with aerobic aromatic potential before adjustment (Spearman's ρ = 0.543, q = 0.0448), but not after accounting for depth and borehole. TPH also showed no significant overall association with the four-dimensional potential profile (partial R² = 0.073, p = 0.349). Site-relative screening identified seven nonexclusive high-burden/low-potential flags across five layers that were robust to threshold and borehole-exclusion tests. In adjusted models, the four-potential block was associated with genus-level community composition (marginal R² = 0.274, p = 0.0337), whereas TPH showed no independent association. These results indicate that petroleum-hydrocarbon burden did not correspond consistently to the four metagenomic degradation potentials. This framework prioritizes subsurface layers for targeted, process-specific assessment of intrinsic bioremediation.