Abstract
Constructed salt marshes as a Nature-Based Solution for coastal defense offer additional benefits over conventional engineering, but project realization is often hampered by practical and governmental obstacles. We assessed the execution of a local-scale salt marsh construction project as a Nature-Based Solution (NBS) with respect to the regional-scale Social-Ecological System (SES) in an explicitly linked NBS-SES framework. A local municipality came up with various plans to develop its waterfront but these proved unrealizable without wider stakeholder participation. Crucial for success was that the local initiative was turned into an NBS integrating livability, biodiversity and flood safety, and that it was linked to the governance systems and actors in a regional SES. The chosen NBS consists of a city beach and two salt marshes, a salt marsh park that is open to the public and a pioneer salt marsh that is only accessible for research. The pioneer salt marsh was constructed by raising the seabed to around mean high tide with sand obtained from a capital dredging project. It was used as a large-scale natural experiment in salt marsh construction. To test the effect of enrichment with silt and clay on initial salt marsh development, six hectare-scale compartments were created in which mud was mixed with sand in the top 1.0 m of the bed to three mud contents of on average 8%, 25% and 48%. Heavy machinery was needed to mix mud through the upper meter of the sandy bed. Mixing mud was softening the sediment causing the machines to sink into the 48% mud enriched bed. To test whether seeding with a pioneer plant species accelerates salt marsh development, fragments of Salicornia procumbens plants were seeded in half of three compartments. Field observations between November 2018 to September 2020 showed that seeding of Salicornia plant fragments resulted in significant differences in vegetation cover and species richness in the first growing season. Mud content showed significant positive effects on vegetation cover and species richness in the two monitored growing seasons, where the compartments with on average 7–9% mud had the lowest vegetation cover and species numbers. When constructing a salt marsh by raising sand and mixing mud, a mud content of 25% is practically feasible and results in high vegetation cover and species richness.
Highlights
Coastal wetlands provide many ecosystem services valued up to US$193,845 ha−1yr−1 [1]
Vertical cores of 1 m with 20 cm interval subsampling for grain composition sampled in November 2018 showed that mixing mud with sand was accomplished throughout the mud was present in the form of peds
In this study we show how we can build back coastal wetlands through large-scale salt marsh construction
Summary
Coastal wetlands provide many ecosystem services valued up to US$193,845 ha−1yr−1 [1]. Depending on the rate of climate change and Nature-Based Solutions 1 (2021) 100005 ing ecosystem services for human wellbeing. Upscaling of nature-based coastal defense offers potential for an increase in coastal wetland area [5], on landscape scale instead of the generally patch-specific approach used at present [6]. Nature-based coastal defense is a component of Nature-Based Solutions (NBS), which were coined by the World Bank as part of their biodiversity portfolio and as a contribution to its work on climate change and adaptation [9]. NBS are defined by the IUCN as “actions to protect, sustainably manage, and restore natural or modified ecosystems, that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits” [10]. Criterion 8 promotes mainstreaming within the appropriate jurisdictional context and linking to sustainability targets [13]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
