by Alicia Pimental
October 01, 2006
The Chesapeake Bay faces environmental threats from over-development, nutrient pollution, chemical contaminants and many other sources. But there is another threat that becomes more evident in many coastal, low-lying areas along the Bay with every passing year: rising sea level.
The Bay, which was formed by the rising sea that flooded the ancient Susquehanna River valley, is constantly being reshaped by erosion. Since the Bay took on its modern form about 6,000 years ago, sea level in the Bay has risen about six inches per century. However, U.S. Geological Survey tide gauge records show that sea level in the Bay rose more rapidly during the 20th century. Currently, sea level at the mouth of the Bay is rising at a rate of about 1.3 feet per century—twice the worldwide average.
This relatively recent increase in sea level rise may have several causes. Land subsidence due to groundwater extraction is one common explanation. Another is human-induced global climate change, which is causing glaciers to melt and ocean volume to increase. Shoreline development that removes or blocks the migration of wetlands can also increase the effects of sea level rise. Without a wetland buffer between the land and the Bay, low-lying areas become more prone to flooding and erosion.
William B. Cronin's The Disappearing Islands of the Chesapeake documents the history and acreage losses due to sea level rise of over 40 Bay islands.
Less than one hundred years ago, Holland Island was a community of over 350 residents, complete with a church schoolhouse, a post office and a community center. In 1914 the island, which lies west of Deal Island in Somerset County, Md., was five miles long and about a mile and a half wide. Around that time, islanders began moving to the mainland to escape erosion that was threatening their homes. Today, Holland Island is less than 100 acres, and the remaining population is made up of terns, egrets, bald eagles and other wildlife.
Despite its name, Barren Island once held a church, a school and more than a dozen farms on its 582 acres. As recently as the 1950s, a fully functional clubhouse welcomed wildfowl hunters to the island, which is located just west of Hoopers Island in Dorchester County, Md. Today, Barren Island has been reduced to less than 120 acres, and the clubhouse is underwater. Recognizing its importance as a wintering ground for several species of ducks, the U.S. Fish and Wildlife Service has made Barren Island part of the Blackwater National Wildlife Refuge (NWR).
Sea level rise is not just threatening the Bay's islands; many low-lying mainland areas are also at risk of being lost. The Blackwater NWR loses about 130 acres of marsh each year to rising sea level. The U.S. Geological Survey forecasts that most of the refuge will be open water in approximately 50 years. Blackwater provides critical habitat to hundreds of species of wildlife, including osprey, hummingbirds, bald eagles and the endangered Delmarva fox squirrel.
While the effects of sea level rise seem dire, efforts are underway to bring back some of the Bay's islands and low-lying coastal areas. Poplar Island, in Talbot County, Md., is being rebuilt by the U.S. Army Corps of Engineers with dredge material from Baltimore Harbor. The island, which served as a retreat for presidents Franklin D. Roosevelt and Harry S. Truman, was once 1,500 acres. By 1997, Poplar Island had become six separate islands totaling about 120 acres. The Poplar Island project, which is expected to be completed in 2016, will restore 1,000 acres of diverse habitat for wildlife that have historically used the island as a nesting and wintering ground.
Will more of the Bay's still-inhabited islands—such as Smith, Hoopers and Tangier—see the same fate as Holland or Poplar islands? Scientists continue to study the causes of sea level rise, as technology develops to combat erosion and restore the land, history and habitat that are being eaten away by the Bay's relentless waves.