Combined effects of earthworm density and zinc on soil functioning

In traditional environmental risk assessment for soils, interactions between biota, contaminants and soil functioning are seldom taken into account. The objective of this study was to investigate effects of zinc (0-620 mg Zn/kg DW) on soil functioning at different densities of the earthworm Lumbricus rubellus. The experiments were conducted using 1L microcosms equipped with respirometers. The presence of earthworms stimulated relevant soil processes: litter loss from the soil surface, litter fragmentation, soil organic matter content and soil respiration. Zinc was not lethal to earthworms, but negatively impacted worm growth and soil respiration. Litter loss from the soil surface was also decreased by zinc. This effect was dependent on worm density. The results of the study clearly indicate that the impact of zinc on soil processes may be modified by the presence and densities of key soil organisms that influence soil organic matter content. The outcome of this research will be used to make existing models for site-specific risk assessment more ecologically relevant, linking population effects of contaminants with effects on ecosystem functioning.