University of Twente Student Theses
Seasonal variation in salt marsh vegetation : impact of physical stressors on the development, decay and seed retention of Salicornia Europaea
Eekman, L.H. (2021) Seasonal variation in salt marsh vegetation : impact of physical stressors on the development, decay and seed retention of Salicornia Europaea.
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| Abstract: | Salt marshes are increasingly being used as (part of) nature based flood defences. A salt marsh is an intertidal area at the coastline with salt-tolerant vegetation species such as Salicornia Europaea. These intertidal areas are flooded during high tide during which the aboveground part of the vegetation might reduce the waves and increase sedimentation rates at the marsh, while the belowground part of the vegetation (roots) prevent the bed from eroding. As Salicornia Europaea is seasonal vegetation, the decay of the aboveground vegetation and the development of the seedbank are important parameters to predict changes in the vegetation cover over the years. To optimise the design and management of salt marshes, it is important to understand the aspects that play a role in the development and decay of the vegetation cover, including the development of the seedbank. Generally, numerical models are used to simulate the development or decay of the vegetation cover to optimise the design and management of salt marshes. Within these numerical models the sudden decay of Salicornia vegetation is simulated going from a fully grown vegetation cover at the end of summer, abruptly to zero vegetation at the start of winter. Whilst the seed availability is simulated using a random constant each year during spring. These assumptions may lead to incorrect predictions as in reality the decay of vegetation might depend on the present vegetation and the different hydro- and morphodynamics. Therefore, the aim of this research is to parameterise the vegetation decay and the seed retention with local hydro- and morphodynamics, like flow velocities, wave height, surface elevation changes and inundation frequency. These parameterisations can be used to predict the development of the seedbank, and with this the development of the vegetation cover in summer, and subsequently the vegetation decay in winter. This leads to the main research question: How do the Salicornia development and decay as well as the seedbank correlate with flow velocities, wave height, surface elevation changes, inundation frequency and sediment composition on a salt marsh throughout the winter period and how do the vegetation characteristics correlate with the Salicornia decay and seedbank? This study is based on field data collected at an artificially created salt marsh near Delfzijl in the northeast of the Netherlands. Waves, tides, flow velocities and bed level changes have been monitored from November 2020 to April 2021. Moreover, vegetation density, length, strength, root length, number of side roots, length of the longest side root and the number of seeds of the dominant Salicornia Europaea have been measured throughout the winter season. The different dynamics and vegetation properties have been correlated by a multiple linear regression analysis to find the driving factors for the development and decay of the vegetation as well as for seed retention. |
| Item Type: | Essay (Master) |
| Faculty: | ET: Engineering Technology |
| Programme: | Civil Engineering and Management MSc (60026) |
| Link to this item: | https://purl.utwente.nl/essays/89040 |
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