A short subway ride from Manhattan, the grasses of the Jamaica Bay salt marsh shelter migratory birds, butterflies and native reptiles. Salt marshes like it are low-lying coastal wetlands covered in tall grasses that can stand daily flooding at high tide — and they are under growing stress as sea level rise accelerates.
Credit: National Park Service.
What marshes do for us
| Benefit | How |
|---|---|
| Storm protection | Marshes buffer storm surges and the wind and wave energy of coastal storms, protecting nearby communities from flooding |
| Cleaner water | They filter excess nutrients and harmful chemicals from agricultural and industrial runoff, leaving cleaner water for fishing, wading and boating |
| Carbon storage | Grasses, shrubs and wildflowers pull carbon from the air; roots and layers of peat lock it below ground for long periods |
| Habitat | Birds, crabs and insects make their homes there |
The race with the sea
Marsh plants need specific conditions. Some grasses tolerate only a certain amount of saltwater flooding, and many can't grow fast enough to keep up with rising water. To survive, a marsh must build its surface upward — through trapped sediment and plant material — at least as fast as the sea rises.
At Assateague Island National Seashore, sea level is rising five to six millimeters a year, and faster every year. Marshes that can't outpace it will drown.
But marshes also move. The seaward edge will eventually be lost, while the upland side expands toward ground better suited to plants. Knowing where that will happen matters as much as knowing how much marsh there will be. "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 postdoctoral fellow at the University of South Carolina (USC).
The model
USC researchers partnered with several Northeast parks — Assateague Island, Cape Cod, Fire Island, and the Jamaica Bay unit of Gateway National Recreation Area — on a marsh resiliency model. Using water levels and precise elevation measurements from permanent markers, the team projects how marsh height will change over time, treating each marsh as part of a larger system and accounting for barriers to its natural movement.
Putting it to work at Jamaica Bay
Nearly 70% of Jamaica Bay's marsh islands had been lost since the 1950s to coastal change and human influence. Since 2003, a multiagency effort has restored 150 acres of marsh there — at a cost of $50 million so far. Park managers need to know whether that work is paying off, and where to restore next.
The model tells them which parts of the park are most likely to gain or lose marsh, so Gateway and the other parks can plan protection and restoration that are practical and sustainable. These parks sit near big cities and smaller communities that depend on their marshes for clean air and water, recreation and storm protection.
Sources
Based on "Studying Salt Marsh Change," by Minh Phan, National Park Service; a work of the United States government in the public domain.
In these publicationsAssateague Island National SeashoreGateway National Recreation AreaCape Cod National SeashoreFire Island National Seashore
Licence: CC0 1.0 (public domain) · Adapted from www.nps.gov
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