Particle tracking in a gap of aquatic vegetation meadow

Abstract

Aquatic vegetation considerably affects the flow field in water bodies, with influence increasing as the depth decreases. As a consequence, vegetation also affects suspended particle transport. In inshore sandy beds less than 40 m deep of the Mediterranean Sea, meadows of Posidonia oceanica are widespread. This plant is constituted by a tuft of very thin and flexible ribbon-like leaves about 1 cm wide and up to 1.5 m long; the meadow areal density can reach 1000-1200 plant/m2. Frequently, such meadows are not continuous but vegetated areas alternate with sand strips (“gaps”). The presence of such discontinuities noticeably affects the flow field and gaps can actually act as particle traps. Some laboratory experiments were performed aiming at studying the flow field in a gap of artificial Posidonia oceanica canopy. In this paper, the measured flow field is used to track single particles within the gap. A simple particle tracking model which assumes no-slip condition and random velocity fluctuations is adopted. A large number of single-particle tracking were performed considering several release elevations of particles as well as several falling velocities of the latters. The examination of the whole tracks allows one to recognize the particle fate as the simulation parameters vary. In spite of the model assumptions, the study gives useful indications on the behavior of a gap towards the suspended particle transport.