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Experiments by Invited Researchers

 

Quantifying the influence of plant traits and patchiness on self-organized coastal landscape formation via bio-physical interactions

Project acronym: HyIII-Delft-10
Name of Group Leader: Stijn Temmerman
User-Project Title: Quantifying the influence of plant traits and patchiness on self-organized coastal landscape formation via bio-physical interactions
Facility: Delta Basin (Multi-directional wave basin)
Proceedings TA Project: Flow interaction with patchy dynamic vegetation: implications for biogeomorphic evolution of coastal wetlands
Data Management Report: There is no Data Management Report available for this project

User-Project Objectives

The scientific objectives of this project were to quantify the spatial flow and wave patterns within and around patches of coastal marsh vegetation, and how these hydrodynamic patterns depend on (1) the size of vegetation patches, (2) the interdistance between patches, and (3) the plant traits of the patches (i.e. plant stem density, height and stiffness). The objective was to quantify these planthydrodynamics interactions under varying conditions of incoming flow velocities and wave heights and periods. The resulting experimental data will be used for further development of models that predict coastal landscape evolution, and that explicitly account for the dynamic feedbacks between coastal vegetation, flow and wave hydrodynamics, and morphodynamics. By doing so, this project should contribute to our understanding of the formation and evolution of coastal marsh landscapes, and their potential value as natural coastal defenses against global change, accelerating sea level rise, increasing storm frequency and intensity, and coastal erosion.

Short description of the work carried out

Overall the objectives of this project are well achieved. During the performance of the project the following difficulties and challenges were encountered. (1) A rather ambitious amount of experiments was originally planned, which lead to a very tight time schedule. This challenged us to optimize the experiments, both in terms of (a) identifying the minimum number of experiments needed to still achieve all scientific objectives; (b) optimizing the
order of experiments so that time-consuming practical handlings (such as changing of the plant box configurations) were kept minimal. (2) This project necessitated several innovative experimental setups that were never used before in the Vinjé basin facility. These included (a) the generation of spatially uniform flow in a large (16 m wide) section of the wave basin, (b) the use of life plant material in the basin, and its practical implications such as potential plant die-off due to limited light availability and too long submergence, (c) logistics to place and change the plant boxes to different spatial configurations within a minimum of time. Thanks to the excellent technical experience and high flexibility of the host institution and other partners involved, all these challenges could be fulfilled with a minor amount of delay. Although this delay lead to some reduction of experiments, all original scientific objectives were sufficiently met.

Highlights of important research results

The results will be published in several papers:

Paper 1: Flow was shown to accelerate next to and in between patches of Spartina anglica. The amount of flow acceleration increases with increasing patch size and decreasing patch interdistance, until a threshold size-distance combination is surpassed below which flow acceleration again decreases. The existence of this threshold behavior explains why at certain places Spartina patches may laterally grow together, while at other places the flow acceleration between growing patches initiates channel erosion and prevents the vegetation patches of growing together.

Paper 2: The amount of flow and wave attenuation and facilitation of plant growth behind Spartina patches was shown to be related to patch size, patch distance and plant density.

Paper 3: The effect of plant traits shows that high, stiff vegetation (Spartina) has more intense effects on flow acceleration next to patches and flow reduction behind patches, compared to low, flexible vegetation (Salicornia, Puccinellia). This explains different growth strategies of plants species with contrasting traits.

Paper 4: Patchy vegetation is more effective in reducing increasing flow velocities within the vegetation, than large closed fields of vegetation. Hence this demonstrates that vegetation patchiness enhances the esilience of coastal vegetation to increasing flow velocities, caused for example by accelerated sea level rise or increasing storminess.

Apart from these direct experimental results, the data will also be used for improvement of modeling of coastal landscape dynamics. This will result in one or two more papers.

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