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Climate Change


Wetlands and intertidal habitat loss

One of the more significant impacts from climate change is wetlands loss due to sea level rise. Delaware Bay is one of the largest estuaries on the east coast of the U.S., second only to the Chesapeake Bay, and both of these estuaries are already losing marshland to rising sea level.

Usually wetlands can keep up with gradual sea level rise through continuous vegetative growth and a healthy sediment supply from upstream rivers and tributaries. If sediment supply into the estuary system becomes reduced, or sea level rise outpaces growth, wetlands can become inundated and, for all intensive purposes, reduced to open-water areas.

A 2002 study by University of Maryland scientists confirms that Delaware is already losing wetlands to sea level rise, and that by the end of the century, many of the Delaware Bay's coastal marshes could disappear.

The Delaware Bay estuary, colored in light blue above, is the second largest estuary on the east coast of the U.S. Its tens of thousands of acres of wetlands and tidal flats support a diverse terrestrial and aquatic wildlife population, making it the most biologically productive ecosystem in the state.

Using sophisticated Landsat Thematic Mapper imagery, scientists have confirmed that rapid degradation of marsh surface in the Delaware Bay occurred between 1984 and 1993. Over that time period, the area of degraded marshes in Delaware Bay increased from 25 percent of the total marshland to 54 percent.

The majority of this loss occurred on the North Shore (the New Jersey side) of the Delaware Bay, with other losses in the lower and middle reaches of the Bay. These losses can be attributed to sea level rise and the diminishing supply of river sediment into the estuary. According to the study, diminished river sediment is a significant problem, and when coupled with continued sea level rise, the Delaware and Chesapeake Bay estuaries may see “the potential collapse of hundreds of thousands of hectares of coastal marsh in the coming decades.” 

According to the EPA, approximately 35 percent of the Delaware Bay estuary’s rare species live in or depend on wetland habitats. Moreover, 70-90 percent of Delaware’s commercial fish and shellfish live entirely in estuarine habitats or use them as nursery grounds.

Also, as many birding enthusiasts know, Delaware Bay has the second largest concentration of migratory shorebirds in the Western Hemisphere, with approximately 1.5 million shorebirds passing through the bay area each spring.

Above: a typical Delaware salt marsh. Although the salt marsh pictured above is quite halthy, a large portion of Delaware’s estuarine marshes are degraded, some severely. Continued sea level rise is just one of the mounting pressures that Delaware’s (and our nation’s) coastal ecosystems must face into the future.

A University of Delaware researcher examines the annual gathering of horseshoe crabs along the Delaware Bay coastline. Horseshoe crab eggs provide vital energy reserves to over a million migratory shorebirds that stop over in the Bay on their spring journey to the Canadian Arctic. But wetlands loss and inundation of intertidal foraging areas could lead to reduced numbers of shorebirds.

These birds also depend on the health of wetlands and the Delaware Bay’s intertidal habitat.

The number of shorebirds visiting the Delaware Bay area has declined drastically in recent years, and scientists are trying to figure out why. Sea level rise impacts, such as degradation of tidal flats and foraging areas, are just one of the mounting pressures that these shorebirds must face into the future.

A 2005 study by Galbraith et al. modeled potential changes in the intertidal foraging habitat for shorebirds visiting Delaware Bay. Even assuming a conservative 2 degrees Celsius global warming scenario over the next century, the study projects “major intertidal habitat losses.” According to the study, an assumed 2۟۟°C warming would result in about a 20 percent loss in intertidal and upland habitat by 2050, and over a 57 percent loss by 2100. If these loses are indeed realized, Delaware Bay tidal flats “could not possibly support shorebird numbers that are even only fractions of their current sizes.” 


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