TY - JOUR

T1 - The effect of successive storm events and seagrass coverage on sediment suspension in a coastal lagoon

AU - Forsberg, Pernille Louise

AU - Ernstsen, Verner Brandbyge

AU - Andersen, Thorbjørn Joest

AU - Winter, Christian

AU - Becker, Marius

AU - Kroon, Aart

PY - 2018

Y1 - 2018

N2 - The effect of a succession of eleven storm events (hourly averaged wind speeds exceeding 10.8ms−1) on thesediment suspension was investigated in a coastal lagoon through in situ measurements of hydro- and sedimentdynamics from a mobile jack-up platform. Results showed that wave-driven bed shear stress (0.1–0.7 Nm−2)was the main driver for sediment suspension in contrast to large-scale flushing, which did not trigger sedimentsuspension. The suspended particulate matter concentration (SPMC) reached a maximum of 200 mg l−1. Ameteorologically-driven lagoonal seiche effect was identified, which could be the driver for advective sedimenttransport in the lagoon. Two major findings for the suspension of sediment can be drawn from the results. First,the energy applied to the bed during successive high-energy storm events caused a reduction in the vegetationcover during a particular strong storm event. This increased the SPMC relative to the bed shear stress, suggestingthat the sediment availability increased. Second, successive high-energy storm events decreased the bed shearstress threshold for sediment suspension subsequent to initial consolidation of the bed, suggesting an increase inthe bed erodibility. The average bed shear stress threshold for sediment suspension was 0.1 Nm−2. Furthermore,successive high-energy storm events increased the SPMC relative to the bed shear stress subsequent to initialconsolidation of the bed, before an ultimate decrease. This suggested that the sediment availability subsequent toinitial consolidation of the bed increased, but ultimately decreased. The impacts were possibly caused by advectivesorting processes during settling of the suspended sediment. The study helps improve numerical modellingof coupled physical and biological environments during successive storm events and thus contributes toadvance coastal management of shallow coastal lagoons under a changing climate.

AB - The effect of a succession of eleven storm events (hourly averaged wind speeds exceeding 10.8ms−1) on thesediment suspension was investigated in a coastal lagoon through in situ measurements of hydro- and sedimentdynamics from a mobile jack-up platform. Results showed that wave-driven bed shear stress (0.1–0.7 Nm−2)was the main driver for sediment suspension in contrast to large-scale flushing, which did not trigger sedimentsuspension. The suspended particulate matter concentration (SPMC) reached a maximum of 200 mg l−1. Ameteorologically-driven lagoonal seiche effect was identified, which could be the driver for advective sedimenttransport in the lagoon. Two major findings for the suspension of sediment can be drawn from the results. First,the energy applied to the bed during successive high-energy storm events caused a reduction in the vegetationcover during a particular strong storm event. This increased the SPMC relative to the bed shear stress, suggestingthat the sediment availability increased. Second, successive high-energy storm events decreased the bed shearstress threshold for sediment suspension subsequent to initial consolidation of the bed, suggesting an increase inthe bed erodibility. The average bed shear stress threshold for sediment suspension was 0.1 Nm−2. Furthermore,successive high-energy storm events increased the SPMC relative to the bed shear stress subsequent to initialconsolidation of the bed, before an ultimate decrease. This suggested that the sediment availability subsequent toinitial consolidation of the bed increased, but ultimately decreased. The impacts were possibly caused by advectivesorting processes during settling of the suspended sediment. The study helps improve numerical modellingof coupled physical and biological environments during successive storm events and thus contributes toadvance coastal management of shallow coastal lagoons under a changing climate.

U2 - 10.1016/j.ecss.2018.07.006

DO - 10.1016/j.ecss.2018.07.006

M3 - Journal article

VL - 212

SP - 329

EP - 340

JO - Estuarine, Coastal and Shelf Science

JF - Estuarine, Coastal and Shelf Science

SN - 0272-7714

ER -