Constructed salt marsh/mudflats

Image courtesy of Luca Noaks. 2023. LAND312 Pūahatanga: Guarding the harbour with natural solutions.

Constructed salt marshes are situated between land and open saltwater, hosting plant species that can withstand regular tidal flooding. These plants are salt-tolerant and play a crucial role in the ecosystem by trapping and binding sediments. Reconstructing salt marshes involves restoring these plant communities and maintaining a balance of salt, water, and sediment levels in the designated area.

Name of NbS

 Constructed salt marsh/mudflats

Type of NbS

 Created or constructed living ecosystems

Location

Salt marshes are typically located along the coastal margins between land and open saltwater, predominantly in higher latitude zones characterized by low-energy shorelines with minimal wave action.

 Source: Salt Ecology. 2022. WAIMEHA/WAIMEA INLET ESTUARY RESTORATION
Orchard Stream Mouth: Restoration Options, Plant Schedule, Restoration Guidance: 3. Available online at:



Relationship to Indigenous knowledge

Salt marshes are vital to coastal areas, serving as crucial ecosystems that not only protect against water surges but also create habitats for numerous species, playing a significant role in the aquatic food web. Additionally, they act as buffer zones that help minimize the impact of coastal flooding on nearby communities.

Climate change benefits
  • Biomass cover loss
  • coastal erosion/wave attenuation
  • storm surge

Although salt marshes are vulnerable to sea level rise, they provide important benefits in the context of climate change. Notably, salt marshes can offer protection against storm surges and help mitigate coastal erosion. Enhancing the salt marsh and mudflat system offers numerous valuable ecosystem services, which are linked to the marsh’s width. Different plant levels in salt marsh systems deliver a variety of environmental benefits. Both the elevation of the marsh and its lateral expansion are key factors in reducing wave energy along coastal regions (Willemsen et al. 2022; Baptist et al. 2021). The functionality of salt marshes relies on the accumulation of sediment, facilitated by the plants. By improving plant density and establishment in constructed salt marsh systems, these ecosystems can develop more effectively and efficiently (Regteren 2020). Constructing salt marshes enhances the variety and density of vegetation at the coastal edge, which leads to an increase in biomass cover. In addition, some research suggests that salt marshes may provide blue carbon storage, i.e. carbon sinks (Raw et al. 2021). These enhancements provide significant societal and ecological benefits, which are further discussed below.

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Societal / socio-cultural benefits
  • Biodiversity health and conservation
  • climate change adaptation
  • disaster risk reduction 

Salt marsh improvement has many leading impacts on the socio-cultural benefits. The increase in vegetation types that include plant species that are herbs, grasses and low shrubs, has benefits for the biodiversity of the environment.  Creating an environment that creates a habitat for fish, birds and invertebrates. Restoring salt marshes improves the biodiversity net gain by improving the integrity and health of the system (Baptist, M.J et al 2021). With this, the plant improvement within the system allows an increase in carbon sequestration and allows adaptation to sea level rise (Baptist, M.J et al 2021). This is due to the system relying on inter-tidal trends to sustain the habitat.

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Ecological and biodiversity benefits
  • Disturbance prevention
  • habitat provision
  • purification of water
  • soil building

Salt marshes are ecologically valuable, with their tidal systems and vegetative buffers mitigating the impact of wave energy and providing habitats for a variety of plant and animal species. They also play a critical role in filtering both natural and human-made nutrients and pollutants in these wetlands (Teixeira et al. 2014). Restoring salt marshes enhances these functions, creating nurturing environments for commercial fish and wildlife, as well as supporting numerous migratory birds (Teixeiraet al. 2014). These ecosystems are crucial for the survival of many species. Furthermore, the vegetation in salt marshes serves as a barrier against wave energy. The success of restoration efforts relies on sufficient sediment accumulation, which allows the ecosystem to develop and stabilize (Regteren, M.V et al 2020). Additionally, these restored areas can act as sinks for heavy metals, helping to naturally filter pollutants from wetlands (Teixeira et al. 2014).

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Technical requirements

This is a complex system requiring expertise and maintenance with specific requirements varying depending upon the scale of the project. It is recommended with the maintenance of the constructed salt marsh ecosystems that between 3-6 monthly site maintenance visits are done over the 2 years after implementation. This is to ensure that weeds are managed, periodically check on the structural integrity, and if needed to reset any plant guards. Please note, however, that this varies.For more details on technical specifications, please refer to additional technical guidance documents, including this report by National Institute of Water & Atmospheric Research Ltd: Technical options for marine coastal habitat restoration in Te Tauihu here: https://www.envirolink.govt.nz/assets/Envirolink/2203-MLDC161-Technical-options-for-marine-coastal-habitat-restoration-in-Te-Tauihu.pdf

Issues and Barriers

Challenges with constructed salt marsh projects can include the problem of weed invasions in restored systems. Therefore, ongoing maintenance is crucial to prevent these invasive species from undermining the restoration efforts.

Opportunities

In Oceania, there are opportunities with this nature-based solution to connect with upstream restorations. As the health of the upstream context has impacts on restored salt marsh areas and can eliminate any work done.

Financial case

A constructed salt marsh project was taken place at the Waikawa estuary in Marlborough. The restoration costs in this project have concluded that it is “offset to some extent by savings made in being able to deposit dredged material locally as part of the shoreline reshaping” (Salt ecology 2021). In the long term, the cost benefits will be future-proof due to preventing and minimizing coastal erosion.

Image courtesy of Luca Noaks. 2023. LAND312 Pūahatanga: Guarding the harbour with natural solutions.
References
  • Baptist, M. J., Dankers, P., Cleveringa, J., Sittoni, L., Willemsen, P. W. J. M., Van Puijenbroek, M. E. B., … & Elschot, K. (2021). Salt marsh construction as a nature-based solution in an estuarine social-ecological system. Nature-Based Solutions1, 100005.
  • Bilkovic, D. M., & Mitchell, M. M. (2017). Designing living shoreline salt marsh ecosystems to promote coastal resilience. In Living shorelines (pp. 293-316). CRC Press.
  • Raw, J. L., Adams, J. B., Bornman, T. G., Riddin, T., & Vanderklift, M. A. (2021). Vulnerability to sea-level rise and the potential for restoration to enhance blue carbon storage in salt marshes of an urban estuary. Estuarine, Coastal and Shelf Science, 260, 107495.
  • Salt ecology. (2021) A summary of salt marsh restoration, Waikawa Estuary, Marlborough (Report No. 081) prepared for Marlborough District Council, August 2021.
  • Teixeira, A., Duarte, B., & Caçador, I. (2014). Salt marshes and Biodiversity. In Sabkha ecosystems (pp. 283-298). Springer, Dordrecht.
  • Willemsen, P. W., Horstman, E. M., Bouma, T. J., Baptist, M. J., Van Puijenbroek, M. E., & Borsje, B. W. (2022). Facilitating salt marsh restoration: the importance of event-based bed level dynamics and seasonal trends in bed level change. Frontiers in Marine Science, 2100.
  • Van Regteren, M., Amptmeijer, D., De Groot, A. V., Baptist, M. J., & Elschot, K. (2020). Where does the salt marsh start? Field-based evidence for the lack of a transitional area between a gradually sloping intertidal flat and salt marsh. Estuarine, Coastal and Shelf Science243, 106909.

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