Spatial distribution of lead in the surface layers of mountain forest soils, an example from the Karkonosze National Park, Poland

Total concentrations and pools of Pb in the surface layers of mountain soils in the Karkonosze National Park are presented and discussed in relation to site altitudes and soil properties. Soil samples were collected from a forest floor and from the depths of 0–10 cm and 10–20 cm in 372 monitoring sites situated in a forested zone of the Park. Particularly high concentrations of Pb (24–200 mg∙kg− 1, most often over 100 mg∙kg− 1), potentially hazardous for soil biota, were found in forest litter. The concentrations of Pb in soil layers 0–10 cm and 10–20 cm were in the ranges 19–248 and 4–196 mg∙kg− 1, respectively. Pb distribution indicated very high spatial variability, confirmed by geostatistical analysis. Calculated pools of Pb varied in a broad range: 0.16–26.6 g∙m− 2 (mean: 6.20 g∙m− 2), and correlated strongly with the stocks of organic matter, both being significantly higher in the lowest altitudinal zone (500–750 m a.s.l.) compared to the highest zone (1250–1380 m a.s.l.). Nevertheless, there was no simple correlation of Pb pools vs. altitude. The largest pools of Pb are stored in the layer 0–10 cm. The pools of accumulated Pb determined in this study are much higher than those assessed on the basis of available data on former and present Pb deposition rates. These findings may be assigned to a seeder–feeder effect and horizontal transport of pollutants. The highest amounts of Pb were identified in three distinct areas (hot spots), in particular in the vicinities of mountain passes, which may be explained by meteorological factors as well as by the influence of local pollution.