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Field experiment on transport and deposition of plastic bottles along mountain river
Summary
Researchers conducted a field experiment tracking plastic bottles released in a mountain river to understand how macroplastic is transported and where it gets stranded. The bottles traveled significant distances but were often retained at bends, log jams, and shallow sections. Understanding transport and deposition patterns in mountain rivers helps identify optimal locations for plastic collection infrastructure.
Information on the transport and deposition of riverine macroplastic is crucial for selecting proper locations for river cleaning actions and for trapping infrastructure installation. Obtaining such information for mountain rivers is of particular importance because their specific characteristics make them particularly prone to illegal dumping, plastic litter input from slope to the river channel, and an increased rate of secondary microplastic production in the river channel (1).To shed some light on the patterns of macroplastic transport and deposition along mountain rivers we have performed a field experiment utilizing tracked plastic (PET) bottles injected to the channel of the mountainous Skawa River in the Polish Carpathians. After 50-57 days of low-flow conditions, we documented transport distances (n=64) which were non-normally distributed and reached from 0.37 km to 16.27 km (median=1.73 km, quartile range=5.29 km). Most of the tracked bottles were deposited on woody debris (71.9%, n=46) (Photo 1) at elevations ranging from 0 to 1.2 m (median=0.4 m, quartile range=0.45 m) above the low-flow water level. Surprisingly, the straight and narrow channelized reach of the studied river trapped 15.3 % of the plastic bottles transported through it, while the highly sinuous, wide unregulated one only 8.7 %, which is probably related to the more frequent contact of woody debris (present in both reaches) with the flowing water, occurring during low-flow conditions within the narrower, channelized reach.Our initial results suggest that places of woody debris deposition along rivers can be a good location for river cleaning actions. Photo 1. The deposition of plastic bottles on wood jam(the Skawa River, S Poland) (photo by M. Liro) References(1) Liro, M., van Emmerik, T.H., Zielonka, A., Gallitelli, L., Mihai, F.C., 2023. The unknown fate of macroplastic in mountain river. Sci. Total Environ. 865, 161224.