Mechanistic Modeling of Marsh Seedling Establishment Provides a Positive Outlook for Coastal Wetland Restoration Under Global Climate Change

Zhan Hu,Lin Yuan,Heng Wang,Bas W Borsje,Yisheng Peng,Michela De Dominicis,Stijn Temmerman,Jim Van Belzen,Tjeerd J Bouma,Pim W J M Willemsen,Judith Wolf

doi:10.1029/2021gl095596

Abstract

AbstractWhile many studies focus on the persistence of coastal wetlands under climate change, similar predictions are lacking for new wetland establishment, despite being critical to restoration. Recent experiments revealed that marsh seedling establishment is driven by a balance between physical disturbance of bed‐level dynamics and seedling root stability. Using machine learning, we quantitatively translate such finding in a new biogeomorphic model to assess marsh establishment extent. This model was validated against multiyear observations of natural seedling‐expansion events at typical sites in the Netherlands and China. Subsequently, synthetic modeling experiments underscored that seedling expansion was primarily determined by controllable local conditions (e.g., sediment supply, local wave height, and tidal flat bathymetry) rather than uncontrollable climate change factors (e.g., change in sea‐level and global wave regime). Thus, science‐based local management measures can facilitate coastal wetland restoration, despite global climate change, shedding hope for managing a variety of coastal ecosystems under similar stresses.

Highlights

Coastal biogeomorphic systems are among the most valuable (Barbier et al, 2008; Borsje et al, 2011), and most vulnerable ecosystems around the globe (Brown et al, 2014; Friess et al, 2019; Parkinson et al, 2017)
Synthetic modeling experiments underscored that seedling expansion was primarily determined by controllable local conditions rather than uncontrollable climate change factors
The results show that in case of sediment deficit (40 mg/L), even without the impacts of relative sea-level rise (RSLR) nor HsR, the tidal flat erodes continuously as previous equilibrium with adequate sediment supply (80 mg/L) is broken (Figure 3a)

Summary

Introduction

Coastal biogeomorphic systems are among the most valuable (Barbier et al, 2008; Borsje et al, 2011), and most vulnerable ecosystems around the globe (Brown et al, 2014; Friess et al, 2019; Parkinson et al, 2017). Tidal marshes are exemplary for these ecosystems, in providing highly valued ecosystem services, such as carbon storage (Kirwan & Mudd, 2012; Mcleod et al, 2011) and flood risk mitigation (Arkema et al, 2015; Smith et al, 2016; Temmerman et al, 2013; van Loon-Steensma et al, 2016; Zhu et al, 2020), while being prominently affected by global climate change. Et al, 2016; Schuerch et al, 2018; Thorne et al, 2018) Such loss may be further exacerbated by increased storminess (Young et al, 2011), global significant wave height rise (HsR) (Young & Ribal, 2019), and reduced sediment supply to the coasts (Ganju et al, 2017; Ladd et al, 2019). While previous studies have advanced the assessment of the loss and retreat of existing marshes (D'Alpaos et al, 2007; Leonardi et al, 2015), further efforts are need to provide science-based strategies to (re)create new marshes and counteract the impacts of global climate change

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