Pollutant - induced changes in terrestrial nematode communities

Abstract

This thesis concerns metal-induced changes in terrestrial nematode communities exposed in microcosm-experiments and in a manipulative field experiment. Indigenous nematode communities, present in freshly collected agricultural soil, were exposed to heavy metals applied singly (Cd, Cu, Ni and Zn) or in combination under different test conditions. Depending on abiotic characteristics such as soil pH and biotic characteristics such as the presence of vegetation, the nematode community structure responded very sensitively to increasing metal concentrations.In general, the effects of the investigated metals were enhanced with increasing exposure time and decreasing soil pH (investigated for Cu only). Furthermore, the presence or absence of vegetation (Lolium perenne L.) seems a very important factor in determining the final ecotoxicological effects of metals to nematodes. In soil covered with L. perenne the effects of Cu and Zn became apparent only at higher metal concentrations, were less severe and were more often caused in an indirect manner. In an acid sandy soil containing Cu and Zn, it was demonstrated that the dissolved Cu or Zn concentrations measured after equilibrating soil samples with a 0.01 M solution of CaCl 2 were not significantly different from single metal additions and that the final effects to the nematode community were all additive or less than additive. Metal-induced reductions in the population size of nematode taxa showed a low intra-taxon variation for the different metals tested. However, there were major differences between the sensitivities of the taxa. For example, some omnivorous and predatory nematodes, known to be "K-strategists", were very sensitive and disappeared at Cu and Zn concentrations exceeding 50 mg kg -1Classifications based on the different lifehistory and feeding groups both facilitated the interpretation of pollution- induced changes in the nematode community, despite the fact that on a lower level these classifications could not adequately predict the sensitivity of all nematode taxa.It is concluded that the nematode community structure and some community parameters, such as the Maturity Index, offer excellent perspectives to assess effects of pollutants at the community level. The nematode community can provide an early and sensitive signal of increased Cu, Ni or Zn pollution in the soil. Moreover, it was demonstrated that the nematode structure may also provide opportunities to identify specific types of disturbance, in casu pollutants