Linking macroplastic deposition to riverbank characteristics

Abstract

Rivers transport, and store a large share of the global plastic pollution. Riverbanks are one of the river compartments where macroplastic litter is deposited and retained. Different factors influence macroplastic deposition on riverbanks. Retention related factors such as riverbank features, and supply related factors, such as hydrometeorology or land-use. Riverbank macrolitter along the Dutch Meuse has been quantified, characterized, and removed biannually since 2017. At each monitored riverbank, macroplastic and other litter items were collected along a 100 m section and classified in over 100 specific litter categories. We assume that after each monitoring round all litter is removed, and that the litter sampled in the following round has accumulated in the time between rounds. This monitoring dataset is analyzed to identify riverbanks with plastic accumulation rates continuously below or above average, and the specific characteristics of these identified riverbanks. Furthermore, correlations are investigated between macroplastic deposition and individual riverbank features and river morphology, such as types of riparian vegetation, or curvature of the river. These correlations are tested for the total amount of plastic litter, but also categories grouped by plastic characteristics such as potential source, density, size, or flexibility. This is done based on the hypothesis that plastic litter items with different characteristics are associated to different processes of plastic emission and deposition. For example, items with low or high density, or different levels of flexibility. Items with low and high densities are transported differently, because their density is lower or higher than the density of water. Items with a high level of flexibility, such as soft plastic foils, have a higher potential for entanglement in vegetation, and a lower potential for remobilization, compared to items with a low level of flexibility. The aim of this study is to identify riverbank characteristics that explain high plastic accumulation rates.