Microplastic Deposition and Transport in a Human-Impacted Stream: Insights from Geomorphic Sinks and Sediment Analogues

Understanding microplastic dynamics in fluvial systems is key for identifying pollution source and potential long-term sink remediation. While many studies rely on controlled experiments (e.g., columns, flumes, tanks), to understand the behavior of this pervasive anthropogenic particle, in-situ investigations remain limited. This research investigates the deposition and transport behavior of microplastics in relation to natural sediments within a small (ca. 7 km) highly anthropogenised stream near Vienna, Austria, serving as a natural field laboratory.

In April 2025, 18 sediment and 7 water samples were collected from diverse geomorphic sinks—such as bars, backwaters, and areas affected by infrastructure. Water sampling was performed using a 150 µm plankton net (30 cm diameter) to capture surface and suspended fractions. A follow-up sampling campaign is planned after a major rainfall event to evaluate sediment reactivation and the potential remobilization of microplastics from these sinks.

Hydrodynamic parameters were measured, and approximately 60 large wood (LW) deposits were mapped and characterized to assess their role in altering flow patterns and sediment connectivity. Microplastics particle shape, size and estimated density will be compared to natural sediments through grain size distribution and total organic content.

Extraction and identification methods include sieving, density separation (1.45 g/cm³), Fenton oxidation, and non-FPA FTIR mapping for polymer identification.

This research explores to what extent microplastics behave analogously to natural sediments in riverine depositional environments. The findings aim to improve our understanding of microplastic behavior in real-world geomorphic contexts and contribute to broader discussions on sediment dynamics in human-impacted river systems.