Many scientists have debated whether coastal wetlands can survive sea-level rise by migrating inland. A new analysis by the Virginia Institute of Marine Science using highly detailed elevation maps of the Chesapeake Bay region shows that—contrary to previous studies—human barriers will do little to slow this marsh migration.
Instead, extensive areas of low-lying rural land will allow coastal marshes to persist or even expand as salty water creeps upward into what are now forests and farmland.
“The numbers are striking,” said lead author Grace Molino, a Ph.D. student at VIMS. “Bay-wide, we expect more than 600 square miles of inundated land in the Chesapeake region by 2100.”
That is four times the area that has converted to marshland in the Chesapeake Bay region since historical observations began in the 1840s, and more than 75 percent will be rural (mainly forests, forested wetlands and farm fields).
Joining Molino on the study, which appears in the latest issue of “Limnology and Oceanography Letters,” are VIMS professor Dr. Matt Kirwan, along with U.S. Geological Survey researchers Joel Carr of Eastern Ecological Science Center and Neil Ganju of the Woods Hole Coastal and Marine Science Center.
The study was made possible with funding from the USGS and collaboration between VIMS and the two USGS Science Centers.
“As far as I know, this is the first projection of inundated land in the bay area, and one of the few and most high-resolution predictions in the U.S.,” said Kirwan. “Our analysis shows that marsh migration is constrained more by natural topography than by human development.”
The authors stressed that their findings apply not just to the mid-Atlantic region, as similar land-use patterns occur all along the U.S. coastline.
“Our data suggests that rural coasts will bear the brunt of sea-level rise nationwide,” said Kirwan.
The study paints the Chesapeake region and North American coastal plain as global outliers in terms of saltmarsh resilience to sea-level rise, with the more urbanized of Europe and Asia more likely to experience “coastal squeeze.” This is the loss of coastal wetlands as rising saltwater floods and erodes their seaward edge while natural or human barriers block their landward migration.
“Despite a perception that urban centers will block marsh migration, our predictions suggest that the most vulnerable land in the Chesapeake Bay remains largely undeveloped, even in what are typically thought of as urban watersheds,” said Kirwan.
“We found that developed lands generally occupy less than 10 percent of predicted migration areas within individual watersheds even under our high scenarios of sea-level rise, despite more extensive development in the watershed overall,” said Molino.
One positive from the study is that the abundance of low-lying forests and farmland in the Chesapeake Bay area and North America more generally will largely preclude coastal squeeze expected to curtail saltmarsh area in other, more urbanized regions of the world’s coast.
The challenge for North American landowners and governments will be to equitably manage the conversion of what is now mostly privately owned, income-producing rural uplands into coastal wetland habitats whose value lies mainly in providing publicly valued ecosystem services such as flood protection and the nurture of fish and bird populations.