In recent years, there's been a surge in removing plastic pollution from rivers, yet few studies delve into their unintended catch of organic matter. In the Scheldt river, plastic removal yields mostly common reed (Phragmites australis), a significant silica accumulator vital for tidal river functioning. Evaluating silica bycatch during plastic removal informs whether the impact of plastic removal has any impact on estuary silica fluxes.

Sampling occurred monthly for a full year period, at three depths across four locations during full ebb or flood phases. Assessing P. australis litter decomposition and silica dissolution from litterbags in the river aided understanding of organic matter's role in estuarine silica cycling.

During all clean-up events together, only 311.6 ± 0.2 g BSi was removed in 50.5 ± 0.1 kgDW organic matter. Extrapolating to the entire river, the average total annual Si flux in transported reed litter was 1242 ± 77 kg BSi year^-1, which still is several orders of magnitude lower than the total annual BSi flux. Spatiotemporal variation, however, led sometimes to more substantial fractions. Litterbag experiments show gradual biomass decline (-50% after ~150 days) and fast BSi dissolution (-50% after ~1 week), which explains the low annual Si flux in reed litter.

The research shows that current organic matter removal as a bycatch of plastic removal isn’t affecting the Si flux in the Scheldt. The role of reed litter is predominantly quick supply of fresh DSi to the ecosystem, which can be important during periods of low DSi in the channel.