TY - JOUR

T1 - Microplastic retention in marine vegetation canopies under breaking irregular waves

AU - Kerpen, Nils b.

AU - Larsen, Bjarke eltard

AU - Schlurmann, Torsten

AU - Paul, Maike

AU - Guler, Hasan gokhan

AU - Goral, Koray deniz

AU - Carstensen, Stefan

AU - Christensen, Erik damgaard

AU - Fuhrman, David r.

N1 - Funding Information: Parts of this research has been financially supported by the Independent Research Fund Denmark project MPCOAST MicroPlastic transport processes in the COASTal environment, grant no. 0136-00227B . The authors likewise acknowledge the support of Lisanne Georgi for assisting during the hydraulic model testing and Maximilian Behnke for 3D-printing the specimen and parts of the set-up. Alexander Schendel contributed with discussions about principle sediment transport mechanisms.

PY - 2024/2/20

Y1 - 2024/2/20

N2 - The present study provides indications and underlying drivers of wave-induced transport and retention potential of microplastic particles (MP) in marine vegetation canopies having different densities. The anthropogenic occurrence of MP in coastal waters is well documented in the recent literature. It is acknowledged that coastal vegetation can serve as a sink for MP due to its energy dissipating features, which can mimic a novel ecosystem service. While the transport behavior of MP in vegetation has previously been investigated to some extent for stationary flow conditions, fundamental investigations for unsteady surf zone flow conditions under irregular waves are still lacking. Herein, we demonstrate by means of hydraulic model tests that a vegetation's retention potential of MP in waves increases with the vegetation shoot density, the MP settling velocity and decreasing wave energy. It is found that particles migrating by traction (predominantly in contact with the bed) are trapped in the wake regions around a canopy, whereas suspended particles are able to pass vegetated areas more easily. Very dense canopies can also promote the passage of MP with diameters larger than the plant spacing, as the canopies then show characteristics of a solid sill and avoid particle penetration. The particle migration ability through a marine vegetation canopy is quantified, and the key drivers are described by an empirical expression based on the particle settling velocity, the canopy length and density. The findings of this study may contribute to improved prediction and assessment of MP accumulation hotspots in vegetated coastal areas and, thus, may help in tracing MP sinks. Such knowledge can be considered a prerequisite to develope methods or new technologies to recover plastic pollutants and rehabilitate valuable coastal environments.

AB - The present study provides indications and underlying drivers of wave-induced transport and retention potential of microplastic particles (MP) in marine vegetation canopies having different densities. The anthropogenic occurrence of MP in coastal waters is well documented in the recent literature. It is acknowledged that coastal vegetation can serve as a sink for MP due to its energy dissipating features, which can mimic a novel ecosystem service. While the transport behavior of MP in vegetation has previously been investigated to some extent for stationary flow conditions, fundamental investigations for unsteady surf zone flow conditions under irregular waves are still lacking. Herein, we demonstrate by means of hydraulic model tests that a vegetation's retention potential of MP in waves increases with the vegetation shoot density, the MP settling velocity and decreasing wave energy. It is found that particles migrating by traction (predominantly in contact with the bed) are trapped in the wake regions around a canopy, whereas suspended particles are able to pass vegetated areas more easily. Very dense canopies can also promote the passage of MP with diameters larger than the plant spacing, as the canopies then show characteristics of a solid sill and avoid particle penetration. The particle migration ability through a marine vegetation canopy is quantified, and the key drivers are described by an empirical expression based on the particle settling velocity, the canopy length and density. The findings of this study may contribute to improved prediction and assessment of MP accumulation hotspots in vegetated coastal areas and, thus, may help in tracing MP sinks. Such knowledge can be considered a prerequisite to develope methods or new technologies to recover plastic pollutants and rehabilitate valuable coastal environments.

KW - Particle transport

KW - Particle retention

KW - Submerged canopy

KW - Canopy density

KW - Canopy flow

KW - Canopy Dean number

KW - Particle Dean number

UR - http://www.scopus.com/inward/record.url?scp=85180547508&partnerID=8YFLogxK

U2 - 10.1016/j.scitotenv.2023.169280

DO - 10.1016/j.scitotenv.2023.169280

M3 - Article

VL - 912

JO - Science of the Total Environment

JF - Science of the Total Environment

SN - 0048-9697

M1 - 169280

ER -