Nina Leestemaker¹˒²*, Johan van de Koppel¹˒³, Daphne van der Wal¹˒²

¹ Royal Netherlands Institute for Sea Research (NIOZ), The Netherlands
² Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, The Netherlands
³ Faculty of Science and Engineering (FSE), University of Groningen, The Netherlands

*Corresponding author: nina.leestemaker@nioz.nl

Introduction

Intertidal wetlands are key coastal ecosystems that support biodiversity, store carbon, and buffer against flooding. Positioned just above mean sea level, they are highly vulnerable to accelerating sea-level rise (SLR). Their long-term persistence depends on maintaining surface elevation through sediment accretion at rates that keep pace with local relative sea-level rise. However, the long-term responses of these ecosystems remain uncertain. 

Objective and Methods

Here, we investigate the adaptive capacity of intertidal wetlands in the Wadden Sea—the world’s largest intertidal system—to cope with sea-level rise. Adaptive capacity is quantified using two indicators: (1) accretion balance, defined as the difference between vertical accretion rate and relative sea-level rise, and (2) long-term trends in inundation frequency derived from satellite imagery.

Accretion rates are obtained from multi-year LiDAR-derived digital elevation models corrected for vertical land movement and validated using Surface Elevation Benchmark (SEB) measurements. Changes in inundation frequency since 1986 are assessed using Landsat imagery. Local relative sea-level rise is calculated from satellite altimetry combined with vertical land movement derived from GPS stations and validated against tide-gauge records.

We compare adaptive capacity along gradients of sediment supply, grain size, wind and wave climate, and tidal range.

Results

We hypothesize that relative sea-level rise will be highest in the Dutch and German Wadden Sea due to subsidence associated with gas extraction, whereas salt marshes in the Danish Wadden Sea will experience lower relative sea-level rise as a result of land uplift. Despite this, higher adaptive capacity is expected in the Dutch and German salt marshes owing to greater sediment input, larger tidal ranges, and stronger winds facilitating sediment transport onto the marsh surface.

By mapping adaptive capacity at the landscape scale, this research identifies vulnerable and resilient zones and provides critical insights for salt marsh restoration and coastal management under accelerating sea-level rise.