Forest soil chemistry, not nitrogen pollution, drives toxic compound buildup
Ramezany S, Houle D, Bellenger JP
Soil Health
The forest floor beneath sugar maples, firs, and spruces acts as the primary filter catching airborne toxic compounds before they reach groundwater, and its capacity depends on the organic layer you're walking on, not on how much nitrogen the trees have absorbed.
Researchers spent over 20 years adding different amounts of nitrogen fertilizer to forest plots in Eastern Canada and then measured how much of a class of toxic compounds, called PAHs, built up in the soil. PAHs drift in from vehicle exhaust and industrial smoke and settle into forest soils over time. The surprise was that extra nitrogen made almost no difference; what really controlled where PAHs ended up was the natural chemistry of the soil itself, especially the spongy organic layers of decomposing leaves and needles near the surface.
Key Findings
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.
chevron_right Technical Summary
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.
Abstract Preview
Original paper
Disentangling the roles of soil edaphic properties and long-term nitrogen addition in controlling polycyclic aromatic hydrocarbons retention in temperate and boreal forest soils of Eastern Canada.
Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants that accumulate in forest soils via atmospheric deposition. However, the combined effects of long-term nitrogen (N) additio...
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