Microbial responses to zinc in soil microcosms with and without a natural assemblage of enchytraeids.

The presence of higher trophic levels in studies on the toxicity on soil contaminants to microbial processes increases ecological realism. This study assessed the toxicity of zinc to soil microbial processes in the presence and absence of enchytraeids (Oligochaeta, Annelida). We incubated microcosms under standard conditions without or inoculated with a natural assemblage of enchytraeid species. Total zinc concentrations of 365 to 1,360 mg/kg caused no mortality of enchytraeids during six weeks' incubation. Soil nitrate concentrations showed a negative trend under zinc addition and soil ammonium concentrations were the highest at zinc concentrations of 1,360 mg/kg, indicating impairment of ammonium oxidation. Zinc decreased bacterial carbon biomass and caused a dose-response decrease of the respiration, but this was not observed in the presence of enchytraeids. Respiration, ammonium concentrations, and soil moisture contents were increased by enchytraeids. We observed no interaction between the addition of zinc and the presence of enchytraeids. The effect of enchytraeids on soil-moisture contents and microbial processes, and the importance of enchytraeid-microbial interactions are discussed. © 2005 SETAC.