Decomposer communities in contaminated soil: Is altered community regulation a proper tool in ecological risk assessment of toxicants? Original Research Article

Effects of patchy soil contamination on decomposer organisms, their community regulation and nutrient mineralization were studied in a microcosm experiment. Coniferous forest soil was patchily contaminated with three concentrations of sodiumpentachlorophenate PCP (0, 50 and 500 mg PCP kg−1 of dry soil). Abundance of microbes, enchytraeids, nematodes, small oribatids and predatory mites were reduced by the PCP. Direct toxicity of PCP and lowered microbial biomass seemed to affect animal community composition in the most contaminated patches. Some large oribatids which seemed to be tolerant to PCP increased their numbers in the most contaminated patches. Although predatory mites suffered from PCP, no altered predator-prey interactions were observed. At the beginning of the experiment more nutrients were released in the patches with highest PCP concentration and the nutrients accumulated in the soil. Soil decomposer food webs seemed to be mainly bottom-up controlled: PCP strongly affects microbes and hence caused changes in the community structure of soil animals and nutrient cycling. Hence top-down orientated ecological models on community regulation and food web dynamics seem to be unsuitable when assessing effects of pesticides on soil communities.