The effect of simulated acid rain on the nutrient status of subarctic woodland soils in eastern Canada

Treatment of small plots in a spruce–lichen woodland near Schefferville over two summers with simulated acid rain at pH 3, 4, and 5.5 and comparison with plots exposed to natural rainfall revealed increased leaching of nutrient cations, especially Mg2+, but only with the pH 3 treatment. Most changes in composition occurred as the solutions passed through the lichen mat with its associated litter and vascular plants. Experiments with laboratory soil columns showed that the subsoil horizons neutralize much of the acidity of the pH 3 treatments, presumably because of sulphate-fixation in the Fe-rich horizons. Based on measurements of field litter decomposition and laboratory carbon dioxide flux, the simulated acid treatments have little effect on organic matter decomposition. The treatments did not affect cation leaching from burnt plant tissues, but in the most acid treatment a larger proportion of the released nutrient cations were lost from the soil column. Laboratory experiments did not detect significant changes in mineralization rates, but there were increased leaching losses of NH4+-N with the pH 3 treatment. Because of the acid nature of the soils (soil pH 4.0), there appear to be few significant changes in soil nutrient status associated with acid rain, but this conclusion must be interpreted with caution because of the relatively short duration of the experiments and the harsh climatic and edaphic environment in which subarctic plants grow.