Deposition and Mobilization of Microplastics in a Low-Energy Fluvial Environment from a Geomorphological Perspective

Abstract

Though microplastic (MP/MiP) pollution of the environment is a popular research topic, a relatively limited number of studies are investigating its geomorphological context. However, site-specific hydrological and morphological parameters fundamentally affect the MP transport, deposition and mobilization. Therefore, we aimed to evaluate the geomorphological influencing factors on MP deposition in the fluvial sediments of the Tisza River (Central Europe). Between the two surveys (in 2019 and 2020), small flood waves rearranged the MP pollution, as in the sediments of the Tisza it decreased by 30% and in the tributaries by 48%. The previously highly polluted upstream and downstream sections became moderately polluted, but the contamination increased in the Middle Tisza, and the hot-spots were rearranged. The increasing longitudinal trend in the MP content exists if the minimum values of the hydrologically uniform sections are considered. The tributaries are important MP sources, as 80% of them had a higher (by 20%) MP content in their sediments than the Tisza had near the confluence, and they increased the MP content of the Tisza by 52% on average. The point-bars were the most polluted in-channel forms, while the side-bars and sediment sheets had less MP content, by 18 and 23%, respectively. The spatial trend of the MP content of these forms was not the same. Therefore, during the planning of sampling campaigns, it is very important to consider the geomorphological setting of a sampling site: we suggest sampling side-bars. No clear connection between the particle size of the sediments and their MP content was found.

Microplastic Contamination of Fine-Grained Sediments and Its Environmental Driving Factors along a Lowland River: Three-Year Monitoring of the Tisza River and Central Europe

“…One of the first complex measurements was carried out by Hurley et al [13], who found that floods effectively redistribute MP pollution within a river system, though this is not spatially uniform. A similar redistribution was observed by Rodrigues et al [20] and Kiss et al [14,21]. Thus, spatially and temporally repeated measurements could be used to identify MP sources and the origin of the pollution, transport and mixing of MPs, their accumulation, hotspot deployment and the main driving factors of these processes.…”

“…The concentration of MP particles transported in rivers is neither spatially nor temporally constant [13,14], as the points could act as sinks or sources [6]. Spatial monitoring, e.g., sampling multiple sites within a water system at a given time, is common [15,16].…”

Comparative Analysis of Riverine Plastic Pollution Combining Citizen Science, Remote Sensing and Water Quality Monitoring Techniques

“…The microplastic content of sediments of the Tisza and its tributaries has been studied systematically since 2019 [30][31][32][33][34][35]. Each summer, a sampling campaign was performed from the source of the Tisza in Ukraine to its confluence in Serbia and in the near-confluence sections of the main tributaries.…”

“…The MaP pollution of the Tisza and the mountainous areas of the catchment were documented by Liro et al [16], Mohsen et al [22] and Magyar et al [27]. Besides, one of the longest and most detailed microplastic surveys of the world was performed in the river system of the Tisza, revealing the MiP transport in the river and its accumulation in the sediments [30][31][32][33][34][35].…”

“…The increased MaP pollution contributes to the increased microplastic pollution of the Tisza River. According to the annually repeated (since 2019) monitoring along the river [30][31][32][33][34], the microplastic pollution of the sediments was the highest in 2019 (3177±1970 items/kg). In the same year, the largest MaP accumulation (18.8 thousand m 2 ) was detected upstream of the Kisköre Dam [22].…”