Budapest University of Technology and EconomicsFaculty of Civil Engineering - Since 1782

Surface waters, from streams to oceans, are increasingly exposed to a wide range of anthropogenic impacts. Human activities alter water flow, the morphology of the water body as well as water quality, eventually affecting the environment. Researchers have better and better understanding of the water and even of the more complex sediment balances of river networks, however, there is still a significant knowledge gap about the dynamics of different pollutants. Among the wide range of river pollutants, plastics represent a significant amount, moreover, our knowledge on the transport processes of plastics is strongly limited. It was only the last 10 years that we recognized that practically all surface waters on the planet are polluted with small to microscopical plastic particles, or in other words: microplastics. Microplastics are plastic items with a characteristic size < 5 mm, which are either directly emitted to the environment or generated by the weathering of larger plastic objects (bags, bottles, etc.). Microplastics are released in the waters in many ways, e.g. from wastewater treatment plans, agricultural drainage or storm drainage, and even atmospheric loading by windblown dust. In streams, plastic particles are exposed to the same hydraulic forcing as sediment grains and therefore their transport should be connected. Thus, as rivers transport sediment grains, they similarly act as pathways for microplastics from the source to the marine environment, which can be considered as a terminal sink. However, rivers themselves can also act as sinks, retaining a significant portion of the microplastic pollution that they receive in their sediments. Plastic particles can cause a high variety of negative effects on the biota, from physical injuries to toxicity. Macroplastics, having a characteristic size of > 5 mm are also transported by rivers, however, the spatio-temporal dynamics of macroplastic transport is very different compared to microplastics. 

The proposed PhD research focuses on the analysis of plastic transport in rivers by means of sophisticated field measurement and computational simulation tools. The candidate has to work out a field sampling method, based on which the quantitative description of microplastic transport is feasible. Through representative case studies, the spatial and temporal behavior of microplastic dynamics has to be analyzed. As for the macroplastics, also a novel field measurement method has to be developed, rather based on video footages, which is capable to identify and quantify the plastic pollution in the main channel as well as on floodplains of rivers. Using the developed field methods, a computational model has to be parameterized and validated to describe the transport processes of the different kinds of plastics, considering the potential sources of the pollution, the river hydrodynamics, and the interaction between the water and solid phases. 

A few relevant questions that should be addressed within the proposed research:

    • Can we quantify the influence of accumulation hotspots, such as groyne fields, floodplains, river bends or side branches on the longitudinal variation of plastic transport? 

    • How are the microplastics being transported in rivers, what is their temporal and spatial behavior? How fast does the microplastic size distribution change along rivers?

    • Deposition of plastics in floodplains? Is there a return from a floodplain?

    • What are dominant forms of microplastic in smaller or larger rivers? If there is a difference, which mechanisms are responsible for the change and at which rate do they act?