Towards Underwater Macroplastic Monitoring Using Echo Sounding

Towards Underwater Macroplastic Monitoring Using Echo Sounding

Broere, S. (TU Delft Rivers, Ports, Waterways and Dredging Engineering)
van Emmerik, Tim (Wageningen University & Research)
González-Fernández, Daniel (University of Cadiz; European University of the Seas)
Luxemburg, W.M.J. (TU Delft Water Resources)
de Schipper, M.A. (TU Delft Coastal Engineering)
Cózar, Andrés (University of Cadiz; European University of the Seas)
van de Giesen, N.C. (TU Delft Water Resources)

2021

Plastics originating from land are mainly transported to the oceans by rivers. The total plastic transport from land to seas remains uncertain because of difficulties in measuring and the lack of standard observation techniques. A large focus in observations is on plastics floating on the water surface. However, an increasing number of observations suggest that large quantities of plastics are transported in suspension, below the water surface. Available underwater plastic monitoring methods use nets or fish traps that need to be deployed below the surface and are labor-intensive. In this research, we explore the use of echo sounding as an innovative low-cost method to quantify and identify suspended macroplastics. Experiments under controlled and natural conditions using a low-cost off-the-shelf echo sounding device show that plastic items can be detected and identified up to 7 m below the river surface. Eight different debris items (metal can, cup, bottles, food wrappers, food container) were characterized based on their reflection signature. Reflectance from plastic items diverged significantly from organic material and non-plastic anthropogenic debris. During a multi-day trial field expedition in the Guadalete river, Spain, we found that between 0.8 and 6.3 m depth considerable quantities of plastics are transported. As most plastic monitoring and removal strategies focus on the upper layer below the surface (up to approximately 1.5 m depth), a substantial share of the total plastic transport may be neglected. With this paper we 1) demonstrate that echo sounding is a promising tool for underwater plastic monitoring, and 2) emphasize the importance of an improved understanding of the existing plastic loads below the surface.

hydrology
macroplastic
marine litter
microplastic
sonar

http://resolver.tudelft.nl/uuid:62870e8c-96cc-4e06-a259-f9aac5fc37cd

https://doi.org/10.3389/feart.2021.628704

2296-6463

Frontiers in earth science, 9

Institutional Repository

journal article

© 2021 S. Broere, Tim van Emmerik, Daniel González-Fernández, W.M.J. Luxemburg, M.A. de Schipper, Andrés Cózar, N.C. van de Giesen