PubMed · 2026-07-10
A 20-year nitrogen-addition experiment in Canadian forests found that soil chemistry and horizon type, not added nitrogen, control how much toxic PAH pollution accumulates in forest soils. Organic layers near the surface hold far more PAHs than deeper mineral layers, and the type of forest stand shapes which soil properties matter most.
Long-term nitrogen addition (>20 years, 3 dose levels) had no statistically robust effect on PAH concentration or vertical distribution across any forest stand or soil horizon tested.
Organic horizons (F and H layers) consistently retained higher PAH concentrations than mineral horizons, with the magnitude of difference varying by forest type (sugar maple, balsam fir, black spruce).
Nitrogen-related soil metrics, organic carbon content, and pH were the strongest forest-specific predictors of PAH retention, confirming natural edaphic factors as dominant controls.
