Floodplains are increasingly recognised as important sinks for microplastics at the interface between terrestrial and aquatic systems, yet their role in the long-term retention and redistribution of microplastics in soils is still poorly understood. In our working group, we investigate the spatial and vertical distribution of microplastics in Rhine floodplain soils by combining field sampling, depth-resolved soil analyses, and hydrodynamic flood modelling. We could show strong spatial heterogeneity, with the highest microplastic concentrations occurring in frequently inundated topographic depressions. While microplastics are mainly enriched in upper soil horizons, their occurrence at depth indicates vertical transport within the soil profile. The patterns further suggest that soil structure, biological activity, and hydrological connectivity interact to control microplastic retention and redistribution in floodplain soils. Overall, these results highlight floodplains as dynamic storage compartments for microplastics in river corridors and illustrate how combining field observations with hydrological modelling helps to understand the fate of these contaminants.

Prof. Dr. Christina Bogner
Institute of Geography
Ecosystem Research
University of Cologne
christina.bogner@uni-koeln.de

Microplastic contamination in soil ecosystems is an increasing environmental concern because MPs can accumulate, interact with soil organisms, and alter soil functions. Microorganisms rapidly colonize microplastic surfaces and form biofilms that alter the particles’ physicochemical properties, potentially affecting their mobility, bioavailability, and degradation. This study investigates the formation of soil-specific biofilms on microplastics using short-term and long-term incubation experiments under different environmental conditions. Additionally, we develop environmentally realistic microplastics via biofilm coatings to simulate natural MPs and enhance the relevance of soil transport experiments. The results strengthen our understanding of how biofilm formation affects the fate of microplastics in floodplain soils.

Rizwan Khaleel
Institute of Geography
Ecosystem Research
University of Cologne
khaleel.rizwan@uni-koeln.de