Quantifying macroplastic accumulation in water hyacinths using three measuring techniques: a comparative approach

, Schreyers Louise, Van Emmerik Tim, Kieu-Le Thuy-Chung, Phung Ngoc Ahn, Thanh Nguyen Luan, Castrop Evelien, Strady Emilie.

Recent studies suggest that water hyacinths play an important role in the transport of macroplastics in freshwater ecosystems. Forming large patches of several meters at the water surface, the water hyacinths tend to aggregate large amounts of debris, including plastic items. Research on this topic is still novel and few studies have quantified the role of the water hyacinths in plastic entrapment and transport. In this paper, we present and compare the results from three measuring techniques, characterizing the contribution of water hyacinths in macroplastic accumulation for the Saigon River. Through a field campaign conducted in Ho Chi Minh City, Vietnam, we combine the use of visual counting, physical sampling and aerial imagery from UAVs. This enabled to estimate the number of items per size and polymer type entangled in the water hyacinths, along with density and spatiotemporal variation metrics. We also discuss the benefits and limits of the measuring techniques and new methods to detect macroplastics in water hyacinths. Furthermore, our research informs floating macroplastic litter studies more broadly by exploring the potential of UAV-based approaches for monitoring plastic debris in riverine ecosystems.

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