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Spatial and temporal variation in sedimentation rate on salt marshes

Postma, F.M. (2009) Spatial and temporal variation in sedimentation rate on salt marshes. Bachelor's Thesis, Biology.

Biol_Bc_2009_FMPostma.pdf - Published Version

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Salt marshes are ecosystems that depend on sedimentation for their growth and survival. The sedimentation rate on the marshes varies both spatially and temporally. The suspended sediment in the water is partly present as flocs of different sizes. The tidal cycle leads to two velocity peaks in the water flow, resulting in a higher suspended sediment concentration (SSC). The SSC is higher during high tide than low tide. Also spring tide, rain and wind-wave activity cause a higher SSC. Furthermore, there is a seasonal pattern in the SSC but this is poorly understood. Flow paths on salt marsh are mainly determined by the creek network, marsh topography and tidal range. In the creeks flow pulses can occur. Elevation determines, in combination with tidal amplitude, the inundation time of the marsh surface, with longer inundation leading in general to higher sedimentation rates. Vegetation decreases the flow speed and turbidity of the water. Higher vegetation density leads to a larger reduction. Because the largest decrease of flow velocity and turbidity is at the vegetation boundary between the creek and the marsh surface, most sediment is deposited next to the creek. This leads to the development of levees and basins. Vegetation further stabilizes the substrate, inhibiting resuspension and erosion. The abilities of plants to trap sediment and to stabilize it, varies between species. Sedimentation itself has a positive effect on the vegetation. Sedimentation rate can be at its maximum during the summer, because of the highest vegetation cover and low storm frequencies. However, it is also observed that the highest sedimentation rates were during the winter as a result of storms mobilizing and transporting sediment. In general, the spatial variation in sedimentation rate is determined by the elevation of the marsh surface, the distance from the marsh edge and the creeks, and the vegetation. The main factors controlling the temporal variation are the weather, the tidal cycle, the tidal range and the seasons.

Item Type: Thesis (Bachelor's Thesis)
Degree programme: Biology
Thesis type: Bachelor's Thesis
Language: English
Date Deposited: 15 Feb 2018 07:28
Last Modified: 15 Feb 2018 07:28

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