Mohammad Wazne

Microplastics are a growing concern in freshwater ecosystems, but the lack of consistent approaches and standardized protocols hampers accurate assessments of their risks. Additionally, there is still limited research on the impact of microplastics on ecosystem functioning. Therefore, this PhD manuscript aims to bridge these gaps by addressing the presence and consequences of microplastics in freshwater environments. The manuscript begins by addressing challenges in investigating microplastics, with an emphasis on methodological advancements. It highlights the lack of standardization and throughput limitations in existing methods for microplastic extraction and sampling. Thus, the study optimizes a current extraction protocol and compares different sampling approaches for microplastics in streambed sediments to facilitate liable inter-study comparisons. Additionally, this research presents a reliable methodology for synthetic polymer identification using Nile red staining, which distinguishes between plastic and non-plastic materials based on fluorescence intensity. This research then investigates the transport and fate of microplastics in streambed rivers, with a focus on the role of the sediment-water interface in temporarily retaining plastic debris. The influence of hydrological and sedimentary factors, particularly hydrological exchanges between surface and ground water at the sediment-water interface (i.e., hyporheic exchanges), on microplastic distribution is examined. Significant variations in microplastic concentrations across different hyporheic exchanges and sediment depths are observed. Finally, the manuscript examines the effect of microplastics on bioturbation and biogeochemical processes at the sediment-water interface. The bioturbation activities of Tubifex tubifex (Oligochaeta, Tubificidae), an important ecosystem engineer, are studied under varying microplastic concentrations in sediments. The research reveals oxidative stress responses and reduced bioturbation activities, resulting in decreased organic matter mineralization and nutrient fluxes. These findings highlight the potential long-term ecological implications of microplastic pollution on ecosystem functioning, an aspect that has received limited attention in previous research.