Responses of the soil decomposer community and decomposition processes to the combined stress of pentachlorophenol and acid precipitation

The combined effects of contamination by pentachlorophenol (PCP) and acid precipitation on soil decomposer communities and decomposition processes were studied. intact soil cores were taken from a coniferous forest in central Finland, enclosed in plastic tube microcosms and dug into the ground. The total set of microcosms was divided in four treatments: (1) contamination with PCP, (2) PCP and two irrigations with strong acid solution, (3) PCP and five irrigations with weak acid solution, and (4) control: irrigations with deionized water. The applications began 8 weeks after initial burial and were completed over a further period of 9 weeks. The microcosms were sampled after 18, 51 and 59 weeks. Soil pH did not decrease consistently with acid deposition. PCP concentrations were not affected by acid deposition. All acid and/or PCP-treated soils contained more NH4+-N than the control soil at the first and second samplings, but there were no differences at the last sampling. There were more enchytraeids in the controls than in other treatments from the second sampling date onwards, that is, after the winter. Collembolan population density was not affected by the treatments while numbers of oribatid, prostigmatid and astigmatid mites were reduced in the stressed soils, but only on the first sampling date. Most of the observed effects on decomposers and nitrogen mineralization were attributable to PCP, but acid deposition may also have been involved through possible effects on the bioavailability of PCP. The imposed anthropogenic stresses, together with winter conditions, were detrimental for enchytraeids. By the end of the experiment decomposer communities together with mosses had mainly recovered. (C) 1998 Elsevier Science B.V.