Abstract
When heavy metals cause damage to soil biology, they can indirectly inhibit the mineralization of nitrogen (N). In order to investigate the horizon-specific effects of heavy metal contamination on the most important binding forms of N, forest soils (Dystric Cambisols) near a historic smelter (Braubach, Germany) were analyzed along a heavy metal gradient. The sampling was carried out across the complete horizons of the organic layer and the mineral topsoil as well as within the uppermost part of the mineral subsoil. The samples were analyzed for heavy metals, enzyme activity (urease and dehydrogenase), total N (Nt), mineral N (NH4-N, NO3-N), and microbial biomass N (Nmic). The sequential extraction of cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) exhibited heavy accumulations of Cd (0.78–9.27 mg kg–1) and Pb (86.3–7867 mg kg–1) near the smelter chimneys. The organic layer was characterized by an extensive immobilization of heavy metals, acidification due to flue gases, and reduced concentrations of Nmic. The mineral topsoil differed by a higher mobility of Cd, Pb, and Zn. This led to an inhibited enzyme activity, a reduced concentration of Nmic, and an accumulation of Nt at highly contaminated sites. The concentrations of NH4-N and NO3-N were not clearly impacted by heavy metal contamination. Due to intensive adsorption of deposited atmospheric heavy metals by the overlying soil horizons, the mineral subsoil presented a stronger spatial limitation of impacts on N binding forms. The investigations highlight the importance of organic cover layers for the retention of atmospheric pollutants.
Published Version
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