Microplastics in Svalbard fjords: influence of hydrodynamics and local pollution sources

The distribution of microplastics was studied in the Svalbard fjords over three years, in July 2021-2023, to assess the role of different sources, particularly rivers, in the fate of microplastics in Arctic coastal waters. Surface microplastics (0-20 cm depth, 0.5-5 mm size) were sampled with a neuston net, alongside subsurface microplastics sampled with a pump system (1.5 m depth, 0.1-5 mm size). The central part of Isfjorden and its branches, including populated and unpopulated fjords, were studied. Different freshwater discharge situations were observed over 3 years. In 2021, no intensive river discharge occurred, whereas in 2022-2023, intense riverine discharge was noted at all study sites. The highest floating microplastics abundance was found in populated Adventfjorden in all years, which testifies to the importance of local sources in the pollution. The maximum concentration (71,400 items/km² or 0.19 items/m³, 0.19 mg/m³) was along the sharp river plume boundary in Adventfjorden in 2022, which was formed by specific hydrophysical conditions. Unpopulated fjords were free of floating microplastics due to river discharge preventing transport inside the fjords. In 2021, under reduced river discharge and prevailing westerly winds, transport from populated Adventfjorden to unpopulated Tempelfjorden intensified, resulting in accumulation of microplastics there. Subsurface microplastics showed a distinct pattern, with the lowest concentrations in the inner fjords and the highest in the central part of Isfjorden. This indicates that the primary source of these microplastics might be long-distance transport or that intense river discharge is flushing microplastics out of the fjords. We conclude that local pollution sources significantly impact Svalbard. Under specific weather conditions, such as wind blowing into the fjord without intensive river runoff, inner fjords can act as potential accumulation sites for microplastics. Arctic rivers flowing through uninhabited areas bring clean water and thereby dilute microplastic pollution in the Arctic Ocean. Also see: https://micro2024.sciencesconf.org/559547/document