Studying Salt Marsh Change

Silhouette of salt marsh and city skyline.

NPS Photo

By Minh Phan

Just a short subway ride away from the hustle and bustle of Manhattan, people can be immersed in nature in the Jamaica Bay salt marsh. The sea of green grasses at Jamaica Bay provide a sanctuary for a diversity of migratory birds, butterflies, and native reptiles.
Salt marshes are low-lying coastal wetlands blanketed by tall grasses that can withstand daily flooding during high tide. These coastal habitats are home to many species of birds, crabs, and insects, and function to protect nearby communities from flooding. In addition, salt marshes provide many benefits including cleaner water and air.

Salt marshes are natural buffers against storm surges and wind and wave energy from coastal storms. They also help to filter out excess nutrients and other harmful chemicals that can seep into coastal waters from agricultural and industrial runoff. This natural filtration system provides cleaner water for fishing, wading, and boating.

Marsh grasses, shrubs, and wildflowers are efficient at removing carbon from the atmosphere. These plants can help offset the carbon emissions released into the air when we burn fossil fuels to power our cars or heat our homes. With mounting carbon dioxide levels in our atmosphere today, the vegetation found in marshland environments play an important role as a natural carbon sink that can absorb carbon from the air and store it in the soil. The extensive system of roots and layers of peat below the marsh surface secure carbon below ground for long periods of time.

There is no doubt marshes are incredibly important to our coastal communities. However, the acceleration of sea level rise brought on by climate change is putting this environment under increased stress. Like any other habitat, the unique marshland system requires specific conditions in order to grow and flourish. Some marshland grasses, however, can only tolerate a certain range of saltwater flooding, and many plants are unable to grow quickly enough to keep us with sea level rise.

Salt marshes are a dynamic coastal habitat, changing with the rise and fall in sediment and water levels. To better understand how salt marshes will evolve in a changing climate and respond to extreme storms, researchers from the University of South Carolina (USC) partnered with several national parks in the Northeast, including Assateague Island, Cape Cod, Fire Island, and the Jamaica Bay unit of Gateway, to implement a marsh resiliency model. Using a variety of information such as water levels and accurate elevation measurements using permanent markers, researchers were able to anticipate how the height of marshlands will change with time.

On Assateague Island National Seashore, sea levels are rising five to six millimeters per year. Sediment and marsh plant material must accumulate at an equal or greater rate to build up vertical elevation so that the marshes can keep pace with sea level rise. With sea level rising faster and faster every year, salt marshes that cannot outpace the rate of sea level rise will drown.

Marshes have the ability to adapt and evolve in response to coastal change. While the seaward portions of salt marshes will ultimately be lost, upland portions of the system will expand and move towards an area more suitable for plant growth. Understanding patterns of these shifts and the many factors that affect the health and stability of marshes is helping researchers predict where these coastal wetlands will move in the future.

“Instead of just saying marshes will increase or decrease in size, we can determine if they are migrating towards a certain area or eroding in another area,” said Dr. Katherine Renken, a post-doctoral fellow at USC explaining the value in modeling marsh conditions.

Nearly 70% of the marsh islands in Jamaica Bay had been lost since the 1950s due to coastal change and human influence. Since 2003, 150 acres of marsh have been restored through a multiagency effort within Jamaica Bay. But with a cost of $50 million so far, NPS managers need to know whether their efforts are working -- and how to prioritize future restoration efforts to ensure they maximize the benefits.

The USC team developed their marsh resiliency model to help managers do just that -- to view these habitats as part of a larger system and to consider barriers to the natural evolution of a salt marsh. Seeing these shifts can help managers better consider protection measures and restoration efforts. At Gateway, for example, the NPS can now make better decisions about how to best protect the Jamaica Bay salt marsh. Using the data shared by researchers, park managers know which areas of the park will most likely experience gains and losses in marshland. This information allows Gateway and other parks to be more strategic and ensure that their actions are practical and sustainable.

These coastal national parks are nestled near large urban centers and smaller communities that rely on salt marshes for clean air and water, recreation, and protection from storms. Studying salt marsh change will help protect these habitats and the coastal treasures nearby.

Last updated: October 19, 2017