Vertical sediment fluxes and wave-induced sediment resuspension in a shallow-water coastal lagoon |
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Authors: | Lars Chresten Lund-Hansen Mona Petersson Wayan Nurjaya |
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Institution: | (1) Biological Oceanography Department, National Institute of Oceanography and Experimental Geophysics, Via A. Piccard, 54, 34010 Trieste, Italy;(2) Regional Environmental Protection Agency – FVG, Piazza Collalto, 15, 33057 Palmanova, Udine, Italy;(3) Department of Biology, University of Trieste, Via A. Valerio, 28/A, 34127 Trieste, Italy |
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Abstract: | The present study describes variations in the vertical fluxes measured concurrently with sediment traps at both a shallow
water (4 m) and a deeper water (7.5 m) position in a coastal lagoon in April 1995. A tripod equipped with five sediment traps
(trap openings at 0.35 m, 0.75 m, 1.05 m, 1.40 m, and 1.80 m above the seabed) was placed at the shallow water position. This
tripod was deployed three times during the study period and deployment periods varied between 2 d and 5 d. The second sediment
trap, placed at the deep water position in the central part of the lagoon, measured vertical flux for intervals of 12 h at
1.4 m above the seabed. The horizontal distance between the sediment traps was 8 km. The average maximum vertical flux at
the shallow water position reached 27.9 g m−2 d−1 during a period of high, westerly wind speeds, and a maximum vertical flux of 16.9 g m−2 d−1 was reached at the deep water position during a period of high, easterly wind speeds. Both strong resuspension events were
closely related to increased wave shear stress derived from surface waves. Maximum wave-induced resuspension rate was 10 times
higher at the shallow water position and 3.8 times higher at the deep water position compared with the net sedimentation rate
in the lagoon. Small resuspension events occurred at the shallow water position during periods of increased current shear
stress, Estimations of conditions for transport of sediment between shallow water and deep water showed that particles must
be resuspended to a height between 3 m and 4 m and that current speeds must be higher than about 0.1 m s−1. An average sedimentation rate of 3.8 g m−2 d−1 was obtained at the shallow water position during a period without wave shear stress and low current shear stress. This rate
measured by sediment traps is similar to a net sedimentation rate in the lagoon of 4.4 g m−2 d−1, which was determined by radiocarbon dating of a sediment core (Kristensen et al. 1995). |
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