Distribution of soil animals in patchily contaminated soil

Distribution of soil animals with respect to patchy chemical contamination was studied in microcosms containing reconstituted coniferous forest floor. Soil materials were defaunated and soil organisms were reinoculated into a mesh basket in the centre of each microcosm. Part of the humus layer was contaminated with three concentrations of sodiumpentachlorophenate (0, 50 or 500 mg PCP kg−1 of dry humus) and put into mesh baskets (two per concentration) around the central patch. No differences in dispersion ability from the reinoculated patch were found between microarthropod species. PCP decreased microbial biomass in the humus. Numbers of collembolans were significantly lower in the contaminated patches than in the clean ones. The same trend was observed in the numbers of other microarthropods (mainly oribatid mites). Microarthropods were found to move intensively in the microcosm and taxa composition in the patches were different between samplings. Although PCP reduced numbers of individuals it did not affect diversity of the microarthropod community. Enchytraeids moved slowly from the central patch and number of individuals was lower in the most contaminated patches than in the other patches. Specimens of Rhabditis spp. were the first nematodes found in the surrounding patches. Later on other bacterial feeding nematodes were dominant in the patches. Species of genus Acrobeloides were dominant nematodes in the highest PCP concentration. It can be concluded that despite relatively good mobility of the soil animals, even small scale patchy contamination in the soil may have an influence on spatial distribution of the animals.