Soil processes as influenced by heavy metals and the composition of soil fauna.
The effects of heavy metals (Cu and Ni) on soil processes were studied experimentally in forest microcosms in Finland as a function of the presence of different groups of soil fauna (nematodes, microarthropods and enchytraeids). The soil respiration rate was measured at intervals and water leachates were analysed twice for mineral-N. At the end of the experiment, the mass loss of birch (Betula pendula) leaf litter was determined. The soil respiration and nitrification rates were significantly affected by heavy metals, with lower rates observed in the contaminated soil (200 + 100 mg/kg Cu + Ni). In contrast, concentrations of ammonium-N were greater in leachate from the contaminated soil compared to the control soil. There were, however, no significant differences in litter mass-loss among metal concentrations. The soil respiration rate was affected only slightly by the composition of the fauna, whilst there were significant differences in the amounts of mineral-N leached from microcosms representing different faunal assemblages. Microcosms containing Cognettia sphagnetorum (Enchytraeidae) released significantly more mineral-N than all the other units in both control and contaminated soils, showing the integral role of enchytraeids in N-dynamics.