Population density and tissue metal concentration of lumbricids in forest soils near a brass mill

Abstract

The effect of metal pollution on species composition, population density, and age structure of earthworms was studied in coniferous forests near a brass mill in SE Sweden. Samples were taken in two biotapes, dominated by Deschampsia flexuosa and Vaccinium myrtillus, respectively, from eight sites at varying distances (175–20 000 m) from the mill. pH and CEC were found to increase in the soil close to the mill. A decrease in the concentration of extractable metals (Zn, Cu, Pb) could be followed up to 1·2 km from the emission source. Copper and lead were analysed in pharynx, gizzard, muscles, clitellum, seminal vesicles and cerebral ganglion of different earthworm species. Generally, the concentration of copper in tissues was higher compared with lead and inversely proportional to the distance from the mill. A substantial metal uptake was found in the vital tissues, such as seminal vesicles and cerebral ganglion. Juveniles tended to have higher metal concentrations compared with adults. Density and biomass of earthworms was proportional to the distance from the mill, especially in the Deschampsia-dominated biotopes. Dendrobaena octaedra was the most abundant lumbricid species but was absent in soils within 1 km from the mill. Data indicate that the reduced density of earthworms near the mill was due to metal toxicity, but food deprivation could not be ruled out as a possible factor. Reasons for decreased density of earthworms at more remote sites are discussed and data on density and soil zinc concentrations are used to predict the density of earthworms at a metal polluted site.