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Ecological recovery of thermically cleaned soil.

Ecologisch herstel van thermisch gereinigde grond


Many contaminated sites in the Netherlands are rigorously cleaned-up by excavation of the hazardous soil and subsequently thermal treatment for destruction of the contaminants. This results in a complete dead product. When the soil is redeposited it has to be recolonized by organisms. To assess the possibilities of ecological recovery of these soils, a field experiment in a grassland was performed during one year in 42 enclosures of 60 cm diameter each. They consisted of a core of the unpolluted grassland soil with the natural micro- and meso- organisms, placed in thermically cleaned soil. Eighteen enclosures were fertilized. Six controls contained no core, but only unpolluted soil or cleaned soil. The colonization by nematodes, other mesofauna, bacteria and vegetation as well as some abiotic parameters were studied. After 100 days the cores contained thousands of nematodes/100 gr dry soil, the fertilized cleaned soil hundreds/100 gr and the unfertilized cleaned soil dozens/100 gr. These quantities did not change during the rest of the experiment. The control with cleaned soil without core contained after one year also dozens of nematodes/100 gr. Because in the cleaned soil plant growth was poor, energy input in the soil was hardly present. After identification, nematodes were classified into functional groups and diversity was measured. It was concluded that 1) Rhabditidae were the first nematodes to colonize the cleaned soil (bacteria-feeding r-strategists) ; 2) nematode species present in the cleaned soil were also found in the core ; 3) wind was an important vector in nematode dispersion ; 4) additions of fertilizer stimulated colonization by nematodes. Thermically cleaned soil is not a good habitat for organisms unless soil is improved with nutrients, organic matter and N-fixing vegetation.

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