Lets delve into the details, observations and stories of nature to spark curiosity and connect to the natural world
Marsh Migration
Coastal wetlands can't keep pace with sea-level rise, and infrastructure is leaving them nowhere to go.
Randall W. Parkinson, Florida International University
Sea Level Rise in Charleston
I recently saw data about Sea Level Rise (SLR) in Charleston that got my attention. According to NOAA, since 2010 sea levels in the southeastern U.S. have risen more quickly than in prior years, and more quickly than expected. Relative sea level in Charleston has increased seven inches since 2010.
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“While SLR was thought of as a slow and gradual process, our results show that ocean dynamics can change regional sea level rapidly, leaving less time for the coastal communities to mitigate and adapt,” said Jianjun Yin, lead researcher and Professor at the University of Arizona.
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Think back to the year 2010​ and time you spent at a boat landing, a boardwalk over the marsh, on the beach. And now imagine the same spot with the water level 7" higher. That is a lot.
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This data startled me. I feel a new urgency to address the SLR challenges facing us.
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There are many consequence of SLR. Most often we think of flooding streets and the loss of land (i.e. housing and businesses) along the coast. The number of flood events in Charleston over the past 10 years is staggering.
Yet because of who I am, my mind goes to the salt marsh, particularly ours in the Lowcountry. Sea level rise, and especially accelerated sea level rise, threatens to destroy the salt marsh ecosystem. That would be devastating.
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I have gathered here some of what we know about the effect of sea level rise on the salt marsh. My hope is that seeing it all in one place will give you an understanding of the threat and ideas for action.
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Loss of the Marsh Would be Devastating
The salt marsh is a critical ecosystem in the Southeast U.S.. It is vital to our way of life here in Charleston. In the Lowcountry, it is our connection with the water.​​​​​​​​​​​​​​​
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The marsh acts as a shield and a sponge in high water weather events, protecting our low-lying properties from the power of storm surges and waves.
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The marsh contributes significantly to our economy through fisheries (75% of seafood harvested in South Carolina spends at least a portion of their life in the salt marsh), and through tourism and recreation.
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And the salt marsh ecosystem is critical to the environment. The habitat filters our water, acts as a nursery for fish, provides safe stopover spots for migrating birds, nesting spots for shorebirds, is home to the marsh population of dolphin, and so much more.
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Accelerated Sea Level Rise Threatens Marsh
Sea levels continuously rise and fall over eons and the tidal salt marsh adjusts itself to accommodate this. There is a vertical and a horizontal component to the marsh's accommodation. In times of rising sea-levels the marsh will accumulate sediment to raise itself up vertically (accretion) and will move horizontally to higher ground (migration). Both are critical. Research shows, however, that with the accelerated SLR we are experiencing, accretion is unlikely to keep up and marshes will drown. As a result the only way for marshes to survive will be to migrate to higher ground. ​
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"In a period of accelerated sea level rise the survival of the salt marshes relies on upland migration." Nature Journal 2018​​
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Unfortunately, man has come along and built houses, roads, etc., on the ground bordering the salt marsh. This development limits the space that the marsh would normally move to.​ Migration is not always possible.
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"We find that marsh loss is nearly inevitable where topographic and anthropogenic barriers limit migration." Geophysical Research Letters, 2016​​​​​​​​
So what actually is marsh migration?
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It starts with the grass. Since marsh grasses are the foundation of the marsh, where the grasses go, so goes the marsh. With salt marsh migration the grasses must move first. The rest of the marsh will follow.
Here is a diagram and further explanation.​​​​​​
If water level rises too quickly, current marshlands will become open water and too wet for marsh plants to survive. If the area inland of the marsh is unimpeded by man-made barriers, such as seawalls, and is high enough to bring the marsh close to or slightly above sea level, then with the right conditions, marsh flora may be able to shift inland. As storms inundate upland areas, upland soils will become saltier, causing dieback of upland plants and creating conditions for marsh plants to grow. Fagherazzi et al., 2019
The grasses of the salt marsh have adapted to live in this salty and wet environment but cannot survive if they are covered by too much salt water for too many hours each day. They need oxygen and fresh water to survive. So as sea levels rise, the grasses are covered in salt water for more hours each day until they drown. For the marsh as a whole to survive, the grasses must spread, by their rhizomes and by seeds, to higher ground where they will reestablish themselves. Then the rest of marsh life can move and survive.
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However, if there is no receptive ground upland of the marsh edge, the marsh cannot migrate, the drowned grass will not be replaced, and the marsh will not survive.
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Marsh Migration - Ideally
Here are some examples of marsh migration (or not) in our own back yard, taken from Google Earth.
2010 View of Marsh
The areas circled in yellow were high marsh in 2010 - receptive ground upland of the marsh grass - available and receptive for the marsh to migrate up to.
2021 View of the Same Marsh
Note in the green circles that the marsh grass has moved up to this ground by 2021, as necessitated by Sea Level Rise.
However, when the upland ground is not available and receptive to new plant growth, we end up with no more marsh grass. Below is an example from Oak Island Creek.
2010 image
You can see the marsh grass on the edge of the creek in front of the shore and wall.
2024 View of the same location
In this image from 14 years later, these areas of marsh grass has died and there is just mud. The marsh was not able to migrate upland.
Protect the Ground Bordering the Salt Marsh
So what are we to do to protect the marsh? We need to protect the ground bordering the marsh so it is there when needed and is in a condition receptive to new grass growth.
We need to limit hard structures and hard edges and maintain a vegetated buffer on that ground. No gravel, cement, no inflexible landscaping, only receptive and healthy soil, preferably inhabited by native plants.
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"When one of these barriers lies along the inland edge of a wetland, it prevents the wetland vegetation from shifting farther inland. Over time, the wetland becomes narrower, until eventually it may disappear under the rising sea." Marshes on the Move, Fuller 2011
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In August 2024, the City of Charleston released The Charleston Water Plan, a road map for the City to address flooding from rising seas and other causes. Even though this was developed by and for the City, it is applicable across the County and nationwide.
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This is a great document. It is best viewed on a computer(it is a story map). Take time to follow the links as you get interested in a topic.
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One of the Key Strategies of the Plan is to "Amplify a "conservation ethic" for the protection and maintenance of the City's natural infrastructure. Incentivize in City projects the conservation, protection, maintenance and restoration of marshes, wetlands, tidal creeks, urban forests, and green spaces, and develop a City-wide marsh migration and sustainability strategy." The Water Plan urges us to act now to protect the marshes we have and to preserve the land to accommodate migration.
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Here is a screenshot from a map in the 'Land' section about marshes and migration.
Map shows where the marsh is at risk, where it might migrate to and even where it will not be able to migrate to because of existing development.​​
Going Forward
There is constant tension in Charleston between protecting the environment and enjoying it. Protecting land for marsh migration will require some who own land on the edge of the marsh to adjust plans for their land, to change their priorities. And it will require many of us to speak up, to educate, to generate ideas that will protect this ground and work to make it a reality.
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Beauty and Risk
People want to live near nature, near its beauty. There is a risk to this, but usually we can ignore it. We often underestimate the powerful force of nature that comes with the beauty.
After the 2024 wildfires in Los Angeles, many are advocating for building those communities back differently, so that there is more protection from wildfires. It will require community wide efforts and individual sacrifices.
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Our situation in the Lowcountry is a bit slower to unfold but involves the same beauty and force of nature. The marsh protects us from violent wet weather. We can continue to live and play close to the water but need to do this in ways that respect the force of nature. This will take community effort and individual sacrifice, but isn't it worth it?
Want to get involved?
I have begun to educate myself and others and to speak up about our need to protect the ground bordering the salt marsh. If you are interested in knowing more, go to Action for Marsh Migration.​​ Also, follow me on Facebook and share your questions, thoughts and ideas. Let us know what you are doing. Lets find, plug into, and create some community energy to protect the salt marsh.