by Wetlands have thrived along the world’s coasts for thousands of years, playing valuable roles in the lives of people and wildlife. They protect the land from storm surge, prevent seawater from contaminating drinking water supplies, and create habitat for birds, fish and threatened species.
A lot of that may be gone in years.
As the planet warms, sea level rises at an ever faster rate. Wetlands have generally kept pace by uplift and inland migration of a few meters per year. But raised roadbeds, cities, farms and rising land may leave wetlands with nowhere to go. Projections of sea level rise for the middle of the century suggest that the water line will shift 15 to 100 times faster than the wetlands have once been displaced.
I have been studying coastal geology and wetlands for over 40 years. The rates of sea level rise we are seeing now mean that parts of today’s coastal wetland ecosystems will be lost to the ocean in the coming years and decades at an unprecedented rate.
Wetland plants were able to keep pace in the past
There are extensive wetlands on the coasts largely because the sea level has been fairly constant for thousands of years.
Wetland plants could easily adapt to small changes in ocean level because these changes were usually less than 1 millimeter per year. The plants naturally create or absorb sediment, building elevation to keep up with the rising seas. Wetland ecosystems are also capable of horizontal migration so they could colonize areas of the coast that were slowly flooded over time.
However, the world’s climate began to change about a century and a half ago. Fossil fuel burning in factories and vehicles released increasing amounts of carbon dioxide into the atmosphere, raising global temperatures. This also warmed the oceans, which greatly contributed to them, and accelerated the melting of glaciers and ice sheets. The combination of thermal expansion of sea water and land ice has contributed to rapid ocean melting, causing sea levels to rise at faster rates.
Water level data collected by the National Oceanic and Atmospheric Administration at gauges distributed along the US coast show that the average rate of sea level rise is now about 10 millimeters per year – much faster than in the past – and it is expected to continue to accelerate. During the second half of the 21st century, scientists expect sea levels to rise by an average of 30 millimeters per year. That’s 30 times faster than it was rising before the Industrial Revolution.
Sea levels are rising faster than wetlands can adapt
Rates of sea level rise along the mid-Atlantic and southeastern US coasts are now faster than most coastal wetland plant communities can build elevation.
Within decades, many of these vital ecosystems are very likely to be drowned. Over time, areas that once had a lush, extensive and contiguous coastal wetland ecosystem will be filled with small, isolated pools that will enlarge, interconnect and eventually transition to open ocean water.
My recent regional analysis of published horizontal rates of wetland migration along the Mid-Atlantic coastal plains and eastern United States in the Gulf of Mexico suggests that wetlands can move inland at annual speeds measured in meters and tens of thousands of meters. In the same areas, however, theoretical rates at which the inland shoreline will move – calculated using NOAA sea level projections in the year 2050 – are between 100 and 150 meters per year. That’s 15 to 100 times faster than wetlands can move.
The inundation models that scientists typically use to simulate coastal wetland resilience to rising seas assume that inland wetlands migrate at the same rate as the shoreline. As a result of my recently completed work, it appears that models have overestimated the resilience of coastal wetlands and that wetland losses this century will be greater than predicted.
Even under the most ambitious scenarios for reducing carbon dioxide emissions, sea level rise is likely to continue to accelerate this century. That means existing wetland ecosystems along our coast will be lost for generations as the climate continues to warm and the oceans rise.
3 ways to protect these precious ecosystems
So what can be done to save our coastal wetlands? What actions can be taken to minimize the loss of these ecologically and economically important areas?
First, land managers could implement programs to acquire or create conservation corridors near areas of existing coastal wetlands. These undeveloped or natural landscapes will provide a pathway for the wetlands to move inland as sea level rises.
Second, it seems ever more urgent to remove man-made structures – roads, levees, levees – that will prevent the landward advance of coastal wetlands.
A project in Oregon did this by removing a clay dike to allow the wetlands to migrate. In South Florida, engineers raised miles of US Highway 41, known locally as the Tamiami Trail, between Miami and Naples to allow water flows that had been cut off to resume.
Finally, in areas historically drained for agriculture and flood control, surface water management projects can restore freshwater flow toward the coastal zone. In South Florida, for example, rainwater in the Everglades prevented salt water from going underground – until extensive canals were built to drain the region for development and agriculture. Several major water management projects are now diverting rainwater back into the Everglades to slow the developing underground salt plume, which can be fatal to freshwater wetland communities and upland plants.
This article is republished from The Conversation, a non-profit, independent news organization that brings you reliable facts and analysis to help you make sense of our complex world. It was written by: Randall W. Parkinson, Florida International University
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Research related to this submission was supported in part by the United States Environmental Protection Agency’s Region 4 Wetland Development Program Grant (#02D16822).
