Effects of pentachlorophenol in forest soil: a microcosm experiment for testing ecosystem responses to anthropogenic stress

Changes in the structure and function of a soil decomposer community and growth of birch (Betula pendula) due to chemical contamination were studied in laboratory microcosms. Sodium pentachlorophenate (PCP) was added to the humus layer of a simulated forest soil at three nominal concentrations (0, 50 and 500 mg kg^-1 dry mass). After two growing periods (48 weeks), there were more small soft-bodied mites, but less collembolans and microbial biomass, in the higher PCP concentration treatment than in the other treatments. Number of enchytraeids were significantly reduced and fungal-feeding nematodes became extinct in the soil with the higher PCP concentration. Soil respiration did not change due to PCP contamination. Diversity of soil fauna tended to decrease with increasing PCP concentration. Number of faunal taxa were not influenced by PCP. Mainly due to reduction of enchytraeids, total animal biomass was significantly lower in the higher PCP concentration treatment than in the other treatments. At week 8, leaching of nutrients was greatest in the higher PCP concentration treatment. At the end of the experiment no significant changes in soil pH and NH_inf4^sup+-N content of the soil were found. Birch growth and N concentration of the leaves were reduced with the higher PCP concentration. We assume that direct toxicity of PCP at the beginning of the experiment and changes in the decomposer community structure (mainly reduction of enchytracids and changes in microflora) due to PCP were responsible for the lowered primary production in the systems.