Peat acidification in Scotland

Abstract

Simulation experiments have shown that soils can become more acid when treated with accelerated loads of acid precipitation^1–3. Field observations, however, give less clearcut answers. Acid deposition is rarely the only variable between sites, and effects are too small for soil pH changes to be measurable over much less than a decade. To circumvent these problems, Hallbacken and Tamm⁴ in Sweden and Billett et al.⁵ in Scotland re-sampled soil profiles in forests after 39–57 years and showed that many surface organic and mineral horizons had acidified, but biological acidification and acid deposition may both be implicated in the observed changes⁵. Here we compare peat acidity and base saturation with modelled acid deposition at 123 sites in Scotland. Peats with highest acidity (pH(CaCl₂)≤3.0) and with lowest base saturation (≤10%) are found mainly where deposited acidity was greater than 0.8 kg H⁺ ha⁻¹ yr⁻¹, providing conclusive evidence that acid deposition plays an important part in the acidification of some soils.