Mercury accumulation in the surface layers of mountain soils: a case study from the Karkonosze Mountains, Poland

The study was aimed to examine total concentrations and pools of Hg in surface layers of soils in the Karkonosze Mountains, dependent on soil properties and site locality. Soil samples were collected from a litter layer and the layers 0-10 cm and 10-20 cm, at 68 sites belonging to the net of a monitoring system, in two separate areas, and in three altitudinal zones: below 900 m, 900-1100 m, and over 1100 m. Air-borne pollution was the major source of mercury in soils. Hg has accumulated mainly in the litter (where its concentrations were the highest), and in the layer 0-10 cm. Hg concentrations in all samples were in the range 0.04-0.97 mg kg⁻¹, with mean values 0.38, 0.28, and 0.14 mg kg⁻¹ for litter and the layers 0-10 cm and 10-20 cm, respectively. The highest Hg concentrations in the litter layer were found in the intermediate altitudinal zone, whereas Hg concentrations in the layer 0-10 cm increased with increasing altitude. Soil quality standard for protected areas (0.50 mg kg⁻¹) was exceeded in a few sites. The pools of Hg accumulated in soils were in the range: 0.8-84.8 mg m⁻², with a mean value of 16.5 mg m⁻², and they correlated strongly with the pools of stored organic matter.