Oct 27, 2009
Caught between the city and the deep blue sea
The outlook for coastal wetlands along the US Atlantic coast appears bleak. A new study shows that from Massachusetts to Florida, the majority of wetlands are likely to be squeezed out of existence, caught between rising sea levels and coastal development.
By 2100 global sea level is projected to have risen by 20 to 60 cm assuming polar ice sheets remain stable, and possibly by more than one metre if ice sheets become unstable. Compared to most of the world, the US Atlantic coast is especially vulnerable to sea-level rise. An unfortunate combination of sandy ocean beaches, muddy bay shores, hurricanes and sinking land means that large chunks of coast are likely to be reclaimed by a rising sea – unless people invest ever-increasing sums of money on projects to hold back the waters.
For people living along the US Atlantic coast this is a troubling choice but for wetland ecosystems it is likely to be a catastrophe. Ordinarily such ecosystems might be able to survive by migrating inland, creating a new wetland on higher ground. But along most of the US Atlantic coast, human development just inland of the wetlands would block this option if – as expected – people choose to protect their homes rather than give them up to the rising sea.
Jim Titus, from the US Environmental Protection Agency (EPA), has been warning coastal residents about this problem since the 1980s. In a new report, published in Environmental Research Letters, Titus and his colleagues have gathered data on land use and coastal policies from 131 state and local agencies. By overlaying this data onto maps of land elevation, they have created detailed maps of the entire coastline, from Massachusetts to Florida, indicating whether people are likely to hold back the sea or allow the rising water to submerge the land.
The maps present a very different picture than suggested by previous studies, which focused solely on land elevation. Maryland is one of the states most vulnerable to the loss of existing coastal wetlands, with many of the barrier islands, spits and coastal headlands liable to go. Ecological gems, such as the Blackwater National Wildlife Refuge, are almost sure to be swamped by rising waters. However, it isn't all bad news for Maryland's wetlands, as the state prohibits coastal development in most rural areas, giving wetlands a chance to migrate inland along much of Chesapeake and Chincoteague bays. Meanwhile, two counties in nearby Delaware ban development in the 100-year floodplain.
In some cases wetlands will be able to migrate inland at first but will eventually run into the barrier of coastal development. To the north in New Jersey, wildlife refuges provide some room for the retreating ecosystems, but eventually the presence of route 9 will make it impossible for the marshlands to migrate inland. "Route 9 is a major highway and no-one is likely to want to give it up," Titus told environmentalresearchweb.
Many of these wetlands are home to an incredible array of plants, animals and birds, ranging from rare marsh grasses to mangrove swamps, and horseshoe crabs to sea turtles. Some species are endemic to North America and could be lost completely if the marshes go.
Holidaymakers also have a major presence along the Atlantic Coast. Ocean City, built on a barrier island along the Maryland coast, has decided to hold back the sea and keep the city where it is, by piling up sand and eventually elevating land and structures. But officials fear that elevating streets will prevent adjacent lands from draining, allowing water to sit and mosquitoes to breed in front yards. Despite this awareness, they currently have no mechanism for encouraging land owners to elevate their lots to avoid this problem. "In a given community, everyone needs to be on the same pathway," said Titus.
In total Titus and his colleagues show that almost 60% of land less than 1 m above the US Atlantic coast is expected to be developed, and thus unavailable for wetland migration inland. Less than 10% of land below 1 m has been set aside for conservation. And the remaining 30% could be developed as well. "This is like 'The charge of the Light Brigade' where people are moving into harm's way, and they know it, but no one gives the signal to change course," said Titus.
Until now it has been common practice for environmental regulators to grant permits to construct shore protection structures, such as sea walls, with the assumption that such structures have no cumulative environmental impact. Now Titus and his colleagues argue that such structures are likely to have a huge environmental impact in the future, by blocking wetland migration.
If sea-level rise were taken into account then Titus and his colleagues believe the wetland policies that previously seemed to comply with federal law would probably violate the Clean Water Act. "Planning for sea-level rise is not just a good idea, the law requires it," he says.
The scientists hope that their maps will serve as an initial benchmark for evaluating the environmental consequences of current policies as sea-level rises, and for revising them to achieve a more coherent result. Some of the most pressing decisions must be made about the 30% of coastal land that is neither developed, nor earmarked for conservation. "If environmental policies must eventually be revised to ensure that wetlands migrate inland, now is the best time for wetland regulators to revise policies to recognize that sea level is rising. It is also a good time for all of us to ask whether this generation should continue to build new communities in vacant land vulnerable to a rising sea," they write in their paper.
• Although EPA funded the underlying research, the letter was neither funded nor endorsed by EPA.
About the author
Kate Ravilious is a contributing editor to environmentalresearchweb.