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Impact on changing soil conditions following inundation on radionuclide and heavy metal (re)mobilization and the interplay with the soil microbiome

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The Grote Nete River is the main collector of the Nete Catchment. It receives the discharges from the rivers Grote Laak (at Geel), the Molse Nete (at Geel) and the Kleine Nete (at Lier) and finally flows into the Rupel River (Rumst). Historical discharges from the nuclear industries located in Mol and Dessel released artificial radionuclides (e.g. 137Cs, 241Am, 60Co) in the Molse Nete between 1960 and 1980, although daily discharge limits were never exceeded. In addition, the former phosphate industry located in Tessenderlo released high concentrations of 226Ra and of several metals (e.g. Cd, Zn, As) in the Grote Laak until the early 1990s. This resulted in an unique contamination complexity of multiple metals, natural and artificial radionuclides and other ions in a meadow of the Grote Nete river basin near Lier located in the Campine region of Belgium. The advent of the Sigmaplan, a large-scale project aiming among others to restore natural buffering of the Nete Valley over the period 2017-2025, renewed the interest in this legacy contamination. Mainly because the (re)construction of a sequence of flooding areas for containing extreme flow events and the recovery of natural areas that served in the past as habitat for different animal and plant species, can result in a remobilization of radionuclides and other contaminants in the environment with potential for an increased environmental transfer.

Radionuclides and metals can exert a persistent pressure on the soil ecosystem. The bioavailability of different radionuclides and metals depends strongly on their speciation, the local geochemistry, soil solution and the soil microbioome. A complex interplay between abiotic and biotic reactions, affected by the physico-chemical parameters in the soil (pH, Eh, organic matter type and content) and the soil microbiome control  the soil-solution equilibrium and bioavailability of each radionuclide and metal for higher organisms. Vice versa, the microbial community can adapt to changing organogeochemical conditions and the local ecosystem. The soil microbiome is essential for a healthy soil ecosystem. Microorganisms have primary functions in biogeochemical cycles, organic matter turnover, formation and maintenance of soil structure and fertility and plant growth. Consequently, changes in the microbial community structure or inhibition of its functions can alter the soil ecosystem.

We recently showed a clear relation between the chemical parameters and the bacterial community structure in different soil samples of the Grote Nete river basin (Lier) in its natural conditions via a combination of an extensive chemical soil analysis and high-throughput technologies. Although no difference in biomass was observed between locations, communities originating from contaminated locations seemed more adapted to metal stressors compared to control communities. Moreover, nitrification, an important microbial process, was affected in the contaminated locations. However, detailed experiments that explain the observed differences and underpin microbial survival in this contaminated area are lacking. Moreover, how the waterlogging conditions will affect the mobility of radionuclides and metals and how this will influence the bioavailability of these contaminants to plants is not yet known.

This project aims to explicate the effects of flooding on the organic and mineralogical geochemistry and on the microbial community, and to understand the impact of related chemical and microbial processes on the (re)mobilization of radionuclides and metals through a thorough understanding of the interplay between the soil microbiome and the ongoing geochemistry. According to the Sigmaplan, reed will be introduced in the flooded areas, and therefore we will link the chemical and biological processes to the transfer to reed plants. Furthermore, this project will assess the ecological impact of long-term radionuclide and metal contamination and predict the ecosystems response to changing conditions. Our results can be implemented in the impact assessments of this contaminated site.

The minimum diploma level of the candidate needs to be

  • Master of sciences

The candidate needs to have a background in

  • Bio-engineering
  • Biology
  • Chemistry

Estimated duration

4 years

Expert group

Microbiology

SCK CEN Mentor

Mijnendonckx Kristel
kmijnend [at] sckcen.be
+32 (0)14 33 21 06

SCK CEN Co-mentor

Impens Nathalie
nimpens [at] sckcen.be
+32 (0)14 33 28 45

Promotor

Springael Dirk
dirk.springael [at] kuleuven.be