Horizontal distribution of copper, nickel and enchytraeid worms in polluted soil

We studied the horizontal distribution of Cu, Ni and enchytraeid worms (Cognettia sphagnetorum, Vejdovsky, Oligochaeta, Enchytraeidae) in forest soil near a Cu–Ni smelter in SW Finland. Soil samples were taken from a polluted site (2 km from the smelter) and a reference area (8 km from the smelter). We used a hierarchical sampling design in the polluted area for studying possible scale-dependent variability in parameters measured, distance between the samples (different scales) being 5, 50 and 500 cm. Distribution of metals was moderately heterogeneous in the polluted soil; coefficient of variances (CV), 26% for Cu and 32% for Ni. Instead, distribution of enchytraeids in the area was highly heterogeneous (CV, 135%) and the variability increased with increasing a distance between the samples: CV increased from 67 to 104% from the smallest to the largest sampling scale. Soil metal concentrations did not correlate with enchytraeid densities in the polluted area. However, three out of our four sampling plots having distance of 500 cm between each other had lower enchytraeid density than the reference area. Results may indicate that C. sphagnetorum has quite low sensitivity to metal pollution, at least on the forest stand scale. On the other hand, enchytraeids may have population dynamics connected to patches (sources–sinks) caused by uneven distribution of metals. This can mitigate the effects of metals on their population densities. Due to importance of enchytraeids in decomposition processes and the fact that usually only one enchytraeid species is present in boreal coniferous forests, they may be appropriate for field monitoring in these humus rich soils. ©