Effects of short flexible seagrass Zostera noltei on flow, erosion and deposition processes determined using flume experiments

Type Article
Date 2015-06
Language English
Author(s) Ganthy FlorianORCID1, 2, 3, Soissons Laura2, Sauriau Pierre-Guy4, Verney Romaric1, Sottolichio Aldo2
Affiliation(s) 1 : IFREMER, Dept Dynam Environm Cotier, Equipe PHYSED, F-29280 Plouzane, France.
2 : Univ Bordeaux, CNRS, EPOC, F-33615 Pessac, France.
3 : IFREMER, LER AR, F-33120 Arcachon, France.
4 : Univ La Rochelle, CNRS, Littoral Environm & Soc LIENSs, F-17000 La Rochelle, France.
5 : Royal Netherlands Inst Sea Res NIOZ Yerseke, Spatial Ecol Dept, AC Yerseke, Netherlands.
Source Sedimentology (0037-0746) (Wiley-blackwell), 2015-06 , Vol. 62 , N. 4 , P. 997-1023
DOI 10.1111/sed.12170
WOS© Times Cited 11
Keyword(s) Arcachon Bay, flexible vegetation, flow modification, flume experiments, France, sediment resuspension, sediment trapping, Zostera noltei
Abstract Innovative flume experiments were conducted in a recirculating straight flume. Zostera noltei meadows were sampled in their natural bed sediments in the field at contrasting stages of their seasonal growth. The aims of this study were: (i) to quantify the combined effects of leaf flexibility and development characteristics of Zostera noltei canopies on their interaction with hydrodynamics; and (ii) to quantify the role of Zostera noltei meadows in suspended sediment trapping and bed sediment resuspension related with changes in hydrodynamic forcing caused by the seasonal development of seagrasses. Velocity within the canopy was significantly damped. The attenuation in velocity ranged from 34 to 87% compared with bare sediments and was associated with a density threshold resulting from the flow-induced canopy reconfiguration. The reduction in flow was higher in dense canopies at higher velocities than in less dense canopies, in which the reduction in flow was greater at low velocities. These contrasted results can be explained by competition between a rough-wall boundary layer caused by the bed and a shear layer caused by the canopy. The velocity attenuation was associated with a two to three-fold increase in bottom shear stress compared with unvegetated sediment. Despite the increase in near-bed turbulence, protection of the sediment against erosion increased under a fully developed meadow, while sediment properties were found to be the main factor controlling erosion in a less developed meadow. Deposition fluxes were higher on the vegetated bed than on bare sediments, and these fluxes increased with leaf density. Fewer freshly deposited sediments were resuspended in vegetated beds, resulting in an increase in net sediment deposition with meadow growth. However, in the case of a very high leaf area index, sediment was mostly deposited on leaves, which facilitated subsequent resuspension and resulted in less efficient sediment trapping than in the less developed meadow.
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Ganthy Florian, Soissons Laura, Sauriau Pierre-Guy, Verney Romaric, Sottolichio Aldo (2015). Effects of short flexible seagrass Zostera noltei on flow, erosion and deposition processes determined using flume experiments. Sedimentology, 62(4), 997-1023. Publisher's official version : https://doi.org/10.1111/sed.12170 , Open Access version : https://archimer.ifremer.fr/doc/00244/35507/