Advancing wetland restoration science

Feb 16, 2023

Sediment addition is a viable option for raising marsh elevation, but it may take a long time for newly established marshes to resemble existing ones, according to a new paper based on years of research and observation in the National Estuarine Research Reserve System.

A recent paper in Estuaries and Coasts sheds light on the practice of adding sediment onto marsh surfaces as a strategy to help them keep pace with rising seas. Based on three years of research at eight Reserves in different regions, the research team found that while sediment addition is a promising restoration approach for many marshes, vegetation can take years to resemble that of healthy natural marshes.

“We caution restoration practitioners to have realistic expectations when they consider using this approach to save a marsh,” says Kenneth Raposa, research coordinator at Rhode Islands’ Narragansett Bay Reserve and the paper’s lead author. “Plants began to recolonize pretty quickly in most of our test plots, but they’ve yet to resemble our reference sites.”

Ultimately, Raposa says, efforts to protect and manage existing marshes are always better than restoring damaged sites. When conservation isn’t a choice, however, thin-layer placement is viable, though it will take time for new marsh communities to resemble mature, long-established ones.

The team also found that sediment taken from land-based quarries can be just as effective as the more commonly used marine sediment dredged from channels, and that thicker layers of added sediment can make marshes more resilient to rising seas without impacting eventual vegetation growth.

Thin-layer placement of dredged sediment is an increasingly common approach to restoration and preservation of marshes in the Gulf of Mexico and Mid-Atlantic, yet questions remain about its long-term utility and impact.

This study builds on earlier work by the team, providing guidance and recommendations on the practice of implementing and monitoring a thin-layer sediment addition project and regulatory policy development. A panel of national experts highlighted the need for pilot tests of this innovative approach across different geographies.

“Ours is a rare example of a restoration experiment coordinated across different sites,” notes Kerstin Wasson, research coordinator at California’s Elkhorn Slough Reserve and senior author on the paper. “These have become more common, but inspired by our stewardship staff, Reserves have become true pioneers of the concept of coordinated restoration science,” she says.

With its capacity for long-term monitoring, diverse biogeography, and strong connections to communities, the Reserve System is an ideal living laboratory for testing and sharing innovative approaches to marsh conservation and restoration.

“With the nation focused on protecting land for future generations, our national network of Reserves is dedicated to sharing tools and knowledge to address our most critical habitat restoration needs,” says Rebecca Roth, executive director at NERRA. “Local research from one Reserve also strengthens the capacity of all 30 sites to serve their communities and leave them more resilient as they contend with our rapidly changing coasts.”

This research was made possible by sustained congressional investment in the NERRS Science Collaborative. By engaging local communities in the research process, NERRS collaborative research projects directly address their needs while advancing estuarine science.

Three years, eight Reserves, hundreds upon hundreds of hours of hard work by scientists and volunteers, and findings that move the science forward is something to smile about!

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ReservesElkhorn Slough, CaliforniaAdvancing wetland restoration science