Restoring ecosystem services in mature salt marshes through topsoil removal

Salt marshes provide essential ecosystem services, but in engineered, sediment-rich estuaries, rapid vertical accretion often leads to a successional trap. This results in climax-dominated, species-poor, elevated salt marshes characterised by reduced inundation and the loss of pioneer habitats. We investigated topsoil removal (30–40 cm) as an ecological engineering strategy to restore habitat heterogeneity in a constrained salt marsh in the Western Scheldt (NL). Over four years, we integrated field monitoring of sedimentation, hydrodynamics and vegetation with wave modelling under 1:10,000-year storm conditions. Results demonstrate that lowering the marsh platform maintained flood safety levels equivalent to the pre-intervention baseline, as the seaward marsh fringe primarily governs wave attenuation. Post-intervention monitoring revealed high vertical accretion rates (1–6 cm yr−1), yet the aimed restored pioneer stage was transient. Within four years, Salicornia spp. were significantly replaced by high-successional Elymus repens. We attribute this successional bypass to restricted tidal drainage and a 10% reduction in peak water levels compared to reference elevations. While topsoil removal effectively rejuvenates mature marshes, we conclude that elevation reduction alone is insufficient for long-term biodiversity gains without enhancing tidal connectivity.