Risk assessment of heavy metals at ecosystem level using Terrestrial Model Ecosystems

Elevated heavy metal levels in soils are suspected to induce shifts in communities and therefore may affect ecosystem processes. However, risk assessment of heavy metal pollution generally focuses on research at the species level. In this investigation we used intact soil cores or terrestrial model ecosystems (TME) to assess the effects of long-term soil pollution on soil communities and ecosystem functions. Our research area has been subjected to heavy metal (Pb, Cu, Zn) pollution during the last 300 years. The cores, differing in pollution levels, were taken from this area and incubated at standard laboratory conditions. The cores were evaluated on their bacteria, nematode and enchytraeid communities and functioning. Soil functioning parameters monitored were nitrification, decomposition, plant productivity and soil respiration. Functioning was related to existing pollution levels. In addition, to assess stability, additional zinc was applied. The total concentration of zinc after this treatment increased the background pollution level. This increase did not result in significant changes in structural aspects, nor affected all ecosystem functions. However, it was shown that these treatments on the soil cores having the highest pollution levels, decreased the decomposition of added substrates. Risk assessment with TMEs can serve as a tool for evaluating effects in an ecologically relevant setting.