Marsh Response to Sea Level Rise

How are the nation’s tidal marshes responding to sea level rise?

A study led by the National Estuarine Research Reserve System explored this question in 85 salt marshes across 17 coastal states and 20 estuaries. The National Marsh Synthesis Team (NAMASTE) found that as sea levels rise and other environmental conditions shift, marshes are undergoing significant changes from low lying areas to uplands. While the degree and type of change differed across regions, marshes in areas with the fastest sea level rise and smallest tidal ranges were found to be the most vulnerable.

The study was sponsored by the NERRS Science Collaborative. Visit them for more tools, products, and information from this project.

ResourcesFind publications, documents, contact information, and other useful tools.
Why This Study?
What We Did
What We Learned
Explore Our Changing Marshes
As marshes change, so do benefits they provide. Explore the many ways healthy salt marshes help people and nature thrive — and why protecting them for future generations matters more than ever.
Clean Water
Healthy Fish & Wildlife
Strong Economies
Storm Protection
Erosion Control
Climate Resilience

Clean Water

Salt marshes are nature’s filters. They trap sediments and soak up pollutants from stormwater runoff before they can reach the ocean. As water filters through a marsh, contaminants are absorbed or broken down, keeping coastal waters cleaner for people and marine life. Studies from New Jersey, Delaware, Mississippi, Chesapeake Bay show that healthy wetlands— including salt marshes—provide millions of dollars in natural water treatment services every year.

Healthy Fish & Wildlife

Salt marshes and estuaries are home to many species of fish and fish and wildlife. About 60% of fish caught commercially and 80% of fish caught by recreational anglers spend part of their lives in an estuary. Iconic birds like osprey, ducks, and herons hunt and nest in marshes, while deer, bobcats, and foxes often pass through, bed down, or feed in coastal wetlands.

Strong Economies

Important coastal industries rely on healthy marshes, including commercial fisheries, tourism, and recreation. Nearly 60% of coastal seafood catch—worth billions each year—depends on estuaries and marshes. The scenic views that marshes provide add property value for residents and draw visitors to enjoy these vibrant coastal places.

Storm Protection

Healthy salt marshes help protect communities from flooding. Natural sponges, they can absorb up to 1.5 million gallons of water per acre—about 2.5 Olympic swimming pools. Their winding channels and dense grasses slow storm surge before it can reach homes and roads. This reduces property damage, saves lives, and prevents an estimated $267 billion in storm damage every year

Erosion Control

Healthy salt marshes slow erosion by acting as a buffer that absorbs wave energy and calms floodwaters. Above ground, marsh plants help slow fast-moving water so sediment can settle; below ground, their roots hold soil in place. When marshes are lost or damaged, nearby properties become more vulnerable to erosion and storm surge. Wetland loss added $430 million in property damage during Hurricane Irma.

Climate Resilience

Salt marshes store carbon naturally and efficiently. Their plants pull carbon dioxide from the air and lock it deep in peat-rich soils, where flooding slows decay and keeps carbon in the ground for generations. Marshes can store carbon up to 10 times faster than tropical forests, making them a smart, natural way to keep working lands and waters healthy for the future.

This project set out to answer four fundamental questions:

  • Are marshes changing across the country?
  • Where are marshes changing the most?
  • Why are marshes changing?
  • How are marshes changing?
Image
Illustration by Taylor Rose Makes Art.

To address these questions, scientists at 21 Reserves and 85 sites collected data using the National Estuarine Research Reserve’s tidal marsh vegetation monitoring protocol. Following thorough data QA/QC (quality assurance and quality control), local changes were documented using data summaries, visualizations, and statistical analyses.

By combining data from sites across the country, the team also provided regional and national analyses. They used a combination of basic summaries, advanced statistical models, and methods for comparing marsh plant communities to find patterns in how vegetation is changing and what’s causing it.

For more on the analysis methods and results at both national and local scales, a technical toolkit and training to help you apply this project's methods to analyze marsh monitoring data, and more resources, visit the NERRS Science Collaborative.

This study found that the majority of our nation’s salt marshes are changing in response to rising seas. Marshes in areas with the fastest rates of sea level rise and the smallest tidal ranges are the most threatened. Those that are flooded more often with saltier waters are losing plant cover more quickly than those in more brackish waters. While these changes varied across estuaries and regions, many marshes are experiencing the changes depicted below.
Dig Deeper
Image
This dashboard explores Reserve-scale trend res and illustrates the importance of national tidal marsh trend analysis.
Marsh Response to Sea Level Rise Over Time
    Image
    Clean Water
    Healthy Fish and Wildlife
    Strong Local Economies
    Healthy tidal marshes support clean water, healthy fish and wildlife, and strong local economies. Dense grasses filter pollution, provide safe nurseries for fish, shelter birds and other animals, and protect upland forests and homes from storms and erosion.
    Illustrations by Taylor Rose Makes Art.
    Image
    Saltwater Pushes Inland
    More Erosion
    More Flooding
    As sea levels rise, marsh plants at lower elevations begin dying off, giving way to mudflats and standing water from increased flooding stress. As saltwater pushes farther inland, plant communities at higher elevations also begin to shift, decreasing in abundance and diversity. As saltwater pushes farther inland, mudflats and ponding appear. All of these shifts can reduce the marsh’s ability to filter water, support fish nurseries, and hold soil in place—making nearby communities more vulnerable to erosion and flooding.
    Illustrations by Taylor Rose Makes Art.
    Image
    Weaker Storm Protection
    Less Habitat for Fish and Wildlife
    Lost Carbon Storage
    With continued sea level rise and no room to move inland, marshes will continue to degrade, decline, and drown. Less marsh means fewer natural filters for clean water, less habitat for fish and wildlife, weaker storm protection, more erosion, and lost carbon storage—all of which can harm coastal economies and communities.
    Illustrations by Taylor Rose Makes Art.

    Regional Trends

    While marshes are changing at all levels across the nation, those in the Northeast and Gulf of Mexico are changing the most, with the fewest changes seen along the West Coast. In some places in the Southeast and the Gulf Coast, mangroves are expanding into marshes, providing a denser understory and altering the ecosystem dynamics.

      Northeast

      Northeast marshes are being lost due, in part, to rising sea levels and increased flooding. Reserve teams in Maine, Massachusetts, New Hampshire and Rhode Island report that low marsh plants are being replaced by mudflats. High marsh areas are experiencing more ponding and less vegetation, and tree dieback is also becoming more common along upper marsh edges. While these plants are migrating upslope, this process appears to be happening too slowly to prevent overall net loss.

      Southeast

      In the Southeast, marsh response to sea level rise and flooding is variable. In North Carolina, low marsh plants are replacing those that once thrived in higher, drier areas. In South Carolina’s ACE Basin, this study observed only small changes so far, though marsh edges are eroding and disappearing. In Eastern Florida, warmer temperatures and stronger storms are allowing mangroves to move into areas once dominated by marshes.

      Gulf Coast

      On the Gulf Coast marshes are changing as sea levels rise, and erosion, storms, and flooding become more severe. Across the region, plant diversity is declining. Along Florida’s panhandle, low lying marshes are changing into seagrass and mangroves habitats. In Mississippi’s Grand Bay, highways and railroads have choked the natural flow of sediment for over a century—now, sea level rise is accelerating marsh loss, with shorelines retreating up to 18 feet a year. In Texas as in Florida mangroves are replacing native marsh plants.

      West Coast

      Along the West Coast, marshes appear to be the least impacted by sea level rise. In California, the rise in sea levels during events like El Niño have caused plant species to shift, such as California cordgrass moving into marshes. In Oregon, rising saltwater is eroding the lower edges of marshes, while plants that prefer fresher water are disappearing. These changes are related to the higher salinity (saltiness) of the water and increased flooding in the lower areas

      Our Changing Marshes

      Discover how marshes near you are changing with this interactive map. Click on a pin to explore local stories about how marsh plants are shifting in response to rising seas and other forces, how these changes affect the benefits marshes provide, and what your Reserve is doing to help protect these vital resources for the future.