Experiment-supported modelling of salt marsh establishment

Abstract

Recently, the use of salt marshes in front of hard structures is increasingly proposed as a more sustainable coastal protection measure. Yet, salt marsh restoration and creation is often hampered by the lack of a thorough understanding of initial vegetation establishment. Recent studies highlight the importance of bed level change for salt marsh development. In this study we continue the examination of the impact of bed level change on salt marsh development, focussing on the prediction of salt marsh establishment and the implications for coastal management. First, a test with Spartina anglica seedlings (Cordgrass) in a wave flume showed that long-term (seasonal) bed level change is more important for seedling survival than direct wave impact at the shoot. Therefore, we subsequently incorporated bed level change in the Windows of Opportunity (WoO) framework. Lastly, this revised WoO framework was applied to the design of the Marconi pioneer salt marsh (The Netherlands). Combining the WoO framework with a morphodynamic model (Delft3D) showed its potential for salt marsh design. The framework can be used to determine whether salt marsh establishment is possible, to find out which conditions are limiting establishment and to design engineering measures creating the conditions that facilitate salt marsh establishment.

Multiple Environmental Variables Affect Germination and Mortality of an Annual Salt Marsh Pioneer: Salicornia procumbens

“…The shaded grey areas correspond to the 95% confidence interval for the predictions S. procumbens are only a few millimetres tall and will be buried completely when sudden sedimentation events occur. Quantifying exact sedimentation thresholds for S. procumbens can be achieved using burial experiments, as exemplified for S. anglica, and will depend on seedling age (Cao et al 2018;Poppema et al 2019). Sedimentation had no direct significant effect on the mortality, but the bed-level variation did significantly increase mortality (Table 1).…”

Pioneering the edges : unravelling how bioturbation, seeds and sediment dynamics affect initial establishment of pioneer vegetation at the salt marsh edge

“…For example, S. anglica is very sensitive to sediment dynamics, i.e. sediment deposition and erosion (Cao et al 2018;Poppema et al 2019). Salicornia spp.…”

“…germination has been found to increase when salinity is reduced (Carter & Ungar 2003), while its seedlings are sensitive to waterlogging (Egan & Ungar 2000a). The windows of opportunity framework focus mainly on physical parameters (Balke et al 2011;Hu et al 2015a;Poppema et al 2019), however, we argue that biological aspects, such as microphytobenthos and bioturbation, may also interfere with successful germination and seedling establishment ( Fig. 1.3).…”

“…Thresholds for the initial establishment of marsh vegetation still need to be identified (Bouma et al 2014;Poppema et al 2019) and this is specifically interesting in the transition zone of two adjacent systems: the un-vegetated intertidal flat and the vegetated salt marsh. The potential for marsh expansion prevails here if pioneer plants are able to establish successfully.…”

“…Vegetation establishment depends on appropriate boundary conditions and thus various factors. Various studies that have identified one or a few factors that affect vegetation establishment are: bioturbation (van Wesenbeeck et al 2007;, an inundation-free period (Wiehe 1935), drought (Silinski et al 2016b), salinity (Baldwin, McKee & Mendelssohn 1996), temperature (Strain et al 2017), freshwater (Carter & Ungar 2003), seed abundance (Wolters et al 2008;Erfanzadeh et al 2010a), soil oxygenation (Lee 2003), grain size (Koop-Jakobsen, Fischer & Wenzhofer 2017), waves and water depth (Zhu et al 2019), sediment dynamics (Cao et al 2018;Poppema et al 2019), elevation (Wang & Temmerman 2013), and algae (Hulzen et al 2006). In the field, all these variables are likely to change over the salt marsh to the tidal flat interface.…”