Spatio-temporal mechanisms of microplastic transport in rivers: from mountains to sewage outflow

Kukkola, Anna (2024). Spatio-temporal mechanisms of microplastic transport in rivers: from mountains to sewage outflow. University of Birmingham. Ph.D.

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Abstract

The spatio-temporal distributions of microplastic (MP) in three river systems affected differently by urbanization were investigated, with the aim of identifying key hydrological and source control effects on MP concentrations and MP loadings. The potential effects of MP on ecosystem health were assessed through a systematic literature review, which enabled recommendations for standardization of field and laboratory studies to be made, including using environmentally representative MP shapes and compositions and suggestion for harmonised toxicity endpoints across taxa. A new modified and faster MP identification method via fluorescent tagging with Nile Red was designed to facilitate fast and reliable MP identification and quantification in rivers and catchments that are affected by anthropogenic activities. This new method was applied to investigate how source and hydrological controls influence downstream transport of MP in remote mountainous catchments, downstream of sewage treatment works and to compare point and diffuse MP source activation across contrasting urban catchments. This research evidenced that human influences including water management can have substantial implications for MP load estimations and should be taken into consideration for quantification of catchment residence times of microplastics and river network contributions to the oceans. The results also highlight the need for MP sampling campaigns to give further consideration to how best to achieve more accurate MP sampling, recommendations for which include sampling of water diversions, and conducting pre-monitoring campaigns capturing flow regimens and possible MP fluctuations occurring during the day, especially at locations with varying flow regimen (such as downstream from sewage treatment works) to gain understanding of the minimum sample requirements to produce representative samples for that particular system. Furthermore, this thesis demonstrates that hydrological catchment size may not be descriptive of the MP sources, as the effect of the catchment can be dominated by the presence of a single point source, such as a sewage treatment works, suggesting that water management can play a much more substantial role than typical hydrometeorological drivers within a catchment. For diffuse urban sources, the thesis demonstrates the importance of hydrometeorological events (e.g., rain events) as controls for MP source activation as well as their transport and connectivity to the river network, and the need for sampling across such events to increase understanding the impact of source activation on overall MP loadings.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):