The following case study is part of a forthcoming NPS handbook on climate change entitled ”Climate Change and Cultural Resources: Impact Assessments and Case Studies.” The original author is Caitlin Smith.
Constructed on a spit of land off the southern tip of Florida, historic Fort Jefferson is the central cultural feature of Dry Tortugas National Park. Often referred to as “The Guardian of the Gulf”, Fort Jefferson was built to protect shipping access to the Gulf, allowing the United States to maintain an important military post in the Gulf of Mexico and Straits of Florida (NPCA 2010). Fort Jefferson was later used as a military prison during the Civil War for Union deserters (NPS.gov 2010, NPCA 2010). Construction of the Fort spanned from 1846 to 1875, but it was never finished or fully armed. Nevertheless, Fort Jefferson represents one of the largest 19th century American masonry fortifications built, as well as one of the many coastal historic sites along the Gulf Coast that are threatened by rising sea levels associated with climate change (NPS.gov 2010, Thronberry-Erhlich 2005).
Climate changes such as warmer air and sea surface temperatures, which are expected to increase the frequency and severity of storms and hurricanes in the Gulf, will impact Dry Tortugas National Park. Storm damage, compounded by an on-going lack of maintenance, may compromise the structural integrity of the Fort. Meanwhile, a projected sea level rise of 0.6 to 1.2 meters over the next 100 years (Loehman and Anderson 2010) will re-configure the shoreline of Garden Key, potentially undermining the structural stability of Fort Jefferson.
The enabling legislation of Dry Tortugas National Park mandates that the National Park Service “protect, stabilize, restore, and interpret Fort Jefferson, an outstanding example of nineteenth century masonry fortification” for the benefit of future generations (NPS.gov 2011). However, due to the low relief of the islands and location in the middle of the Gulf of Mexico, Fort Jefferson is exceptionally vulnerable to weathering and damage (Climate Change Response Program 2011). Regular exposure to salt, heat, destructive weather and moisture constantly threaten the masonry construction of the Fort. Already, large sections of the Fort Walls have collapsed into the moat surrounding the Fort, due to rusting of the historic Totten shutter system (NPS.gov 2010).
Sea level rise poses a significant threat to the Fort. The seven islands of Dry Tortugas are under constant threat of inundation. Several of the islands disappear seasonally due to rising seas including Middle Key. Bird Key has disappeared altogether (Thornberry-Erhlich 2005). Sediment transport dynamics associated with the coastal environment also present preservation challenges. Shifting sands continually alter the shape and profile of the islands. Sand erodes from one beach and is deposited elsewhere in the course of a single storm event, often causing subsidence and other damage to the Fort’s moat wall (Thornberry-Erhlich 2005).
What is the best way to preserve the structure of Fort Jefferson from rising seas? Dredging the channel between Garden and Bush Key may help protect the structural stability and historical integrity of Fort Jefferson, but could have devastating effects on the local ecosystem (Thornberry-Erhlich 2005). How long can the Fort be protected until it is consumed by the rising waters of the Gulf? Thoughtful conservation, maintenance, and documentation efforts are underway, however, models indicate that Fort Jefferson will experience further damage as a result of increasing hurricane frequency and intensity and, by the end of the century, may be partially under water (Berenfeld 2008).
1. Berenfeld, Michelle L. Climate Change and Cultural Heritage: Local Evidence, Global Responses, The George Wright Forum 2008, vol. 25, no. 2 p. 66-82
2. Loehman, Rachel and Greer Anderson, Understanding the science of climate change: Talking points -impacts to The Gulf Coast, Natural Resource Report NPS/NRPC/NRR—2010/224. National Park Service: 2010, Fort Collins, Colorado
3. National Parks Conservation Association (NPCA), Dry Tortugas National Park, last modified 2010, http://www.npca.org/parks/dry-tortugas-national-park.html
4. NPS.gov Dry Tortugas National Park, History and Culture, Fort Jefferson Preservation, last modified December 9, 2010http://www.nps.gov/drto/historyculture/fort-jefferson-preservation.htm
5. NPS Climate Change Response Program, Dry Tortugas National Park, last modified May 5, 2011 http://www.nps.gov/climatechange/gulfcoast.cfm
6. Thornberry-Ehrlich, Trista L. “Dry Tortugas National Park Geologic Resource Management Issues Scoping Summary” Colorado State University- Geologic Resource Evaluation, January 31, 2005