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Filter effect of Rhine floodplain vegetation on microplastic deposition during a single flood event in Germany
Summary
Researchers studied how Rhine floodplain vegetation filtered microplastic deposition during a single flood event in Germany, documenting that plant cover created distinct spatial deposition patterns and acted as a significant physical barrier concentrating particles compared to unvegetated floodplain surfaces.
Many studies have shown that rivers are affected by microplastic contamination. They can transport microplastics but also act as reservoirs where microplastics can accumulate in river beds and banks, temporarily and for long-term. During flooding, these microplastics can be re-mobilized with the sediments and can be re-deposited in floodplains or transported further downstream. While recent studies suggested that the distribution of microplastics in floodplains is controlled by local topography and flood frequency, the role of vegetation cover in the spatial distribution of microplastics is not known. Therefore, we assume that the vegetation cover of the floodplain plays a crucial role for the retention and deposition of flood-introduced microplastics. Additionally, this important aspect for understanding the transport and subsequent long-term accumulation of microplastics in floodplains has not been addressed so far. Thus, this study aims to investigate the filter effect of floodplain grassland vegetation on the deposition of microplastics and natural sediments during a single major river flood. Therefore, we collected vegetation samples with flood deposits in a Rhine floodplain in Northern Cologne (Germany) after a summer flooding in 2021. Control samples were taken from a non-flooded part of the floodplain. The deposits were washed off the plants and the microplastics extracted via density separation. Additionally, we applied an enzymatic-oxidative purification before analysing microplastics in the samples with µ-FPA-FTIR imaging. Our study shows that, (i) higher vegetation biomass led to an increased deposition of natural sediments and small microplastics, (ii) natural sediments and small microplastics seem to follow different sedimentation mechanisms, (iii) comparison with control samples allowed to distinguish between fluvial and atmospheric deposition on grassland by numbers, shape, and size of microplastics. These important information add up to the understanding of microplastic transport, retention and subsequent long-term accumulation of microplastics in floodplains at the interface of fluvial and terrestrial ecosystems. Also see: https://micro2024.sciencesconf.org/559074/document