In 2019, Georgia placed 5,000 cubic yards of dredged sediment on a 5-acre salt marsh; six years later, it remained about 12 cm higher, with plant growth similar to nearby marshes

Wetlands along the coast play an important role in some of nature's most precious services. They absorb storm surges, store carbon, filter wastes, and serve as habitat for numerous living species. However, many of these habitats are gradually losing height due to rising sea levels and diminishing supply of coastal sediments. Therefore, Researchers are also investigating whether natural restoration techniques can help restore these ecosystems.

As per information provided by the U.S. Army Corps of Engineers (USACE), a 2019 project in Jekyll Island aimed to test this assumption. The method used was to put 5,000 cubic yards of dredged sediment on a marsh area of 5 acres. Six years later, the study showed that the marsh had retained a height of 12 cm. The findings suggest that carefully placing sediment on vulnerable wetlands may offer a practical way to strengthen coastal ecosystems against the long-term effects of rising seas.

Giving a struggling marsh a lift


Due to sediment deposition and the vegetation’s ability to retain organic material, salt marshes are able to gain elevation through natural processes. However, it happens that due to the rising of sea levels, many marshes cannot adapt to changes in water levels. As part of a project in Georgia, scientists tried to reverse this process using a technique called thin-layer deposition that involves the placement of a thin layer of sediment on an existing marsh, thus preventing its disposal elsewhere.

The sediments used in the project were obtained from regular maintenance of navigation channels. Instead of disposing of the dredged sediment at a disposal site, engineers repurposed the material to raise the marsh surface with minimum impact on its ecosystem. The layer of sediments was very thin, allowing the marsh's natural vegetation to recover as plants adapted to the new conditions.

Monitoring recovery over six years

The restoration of a marsh requires extensive efforts beyond just the application of sediment. In order to determine if the ecosystem operates as it should, scientists need to observe and analyze changes in marsh height while observing vegetation recovering over time. The results were positive. Six years after the sediment was added to the marsh, and the surface was found to be about 12 cm higher than it had been before. The height, density, as well as the biomass of the plant stems were at levels similar to those of adjacent untreated marshes, thus indicating that the plant life had recovered. Furthermore, through constant monitoring over a long period, sediment stability was noticed, which brought back the functionality of the marsh ecosystem.

Why elevation matters

Even the slightest change in elevation of salt marshes can dictate the plant’s survival. If the marsh level is insufficient relative to sea level, the marsh remains underwater for an extended time and oxygen concentration in the soil decreases, preventing the plants from developing properly. Healthy marsh vegetation, meanwhile, stabilizes the sediments by means of its root systems, which creates a feedback mechanism responsible for the wetland's capacity for sustainable development. Thus, maintaining elevation is crucial because it helps reduce the risk of coastal marshes being submerged over time.

Importance of nature-based restoration

An article from the U.S. Geological Survey (USGS) states that sediment nourishment is gaining traction as a potential solution for preserving the habitats of wildlife habitats, while at the same time enhancing water quality and carbon sequestration. Unlike methods that are generally used for shore protection, sediment nourishment technologies bring about enhancement of the natural environment.

However, the Jekyll Island project is an illustration of how the material previously used merely for dredging can be used as a means for restoration processes. By not compromising the ecosystem, sediment recovery technologies are implemented successfully and serve as an example of the good cooperation between various natural and engineering mechanisms that can ensure restoration.