What's Happening to Cape Sable?

One of the most drastic changes in landscape in Everglades National Park, and one that is complicated by sea level rise and inland effects, is seen in the Cape Sable area. The Cape is a large coastal landmass located at the southwestern tip of Florida that was once characterized by an expansive interior freshwater marsh and associated freshwater lakes. In the early 1900s, settlers determined to use the area for agriculture began draining the freshwater out to the ocean so the land could dry7. It turns out, the canals they built-coupled with the effects of hurricanes and the manipulation of water farther north-have transformed the coastal system of Cape Sable, and much of this alteration has been aggravated by climate change.

Scientists have used certain clues buried in the geology of the landscape to estimate sea level long before humans had instruments to do so. This analysis shows that sea level rise in south Florida was relatively slow over the past 3200 years7. But our modern instrumentation has recorded an accelerated rate of rise over the past century, which has had visible impacts on Cape Sable. The canals are now a pathway for salty ocean water and sediments to travel inland, especially during high tides or with the help of strong wind and surge from tropical storms7. In recent years, the interior freshwater marsh has disappeared almost entirely, and nearby lakes have filled almost completely with marine sediments. Changes along the Cape also have implications for the mangrove trees that live at the waters edge. In response to rising seas and increased flooding, the trees have been moving inland as the habitat becomes more suitable. And along the coast, high tides and storm surges have helped wash away sediments awry from their roots and have contributed to erosion along Cape Sable7. While many wonder whether coastal plants and mangrove forests will be able to keep pace with sea level rise, others are beginning to notice similar changes further inland.

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These images show the expansion of Middle Cape Canal, the retreat of the shoreline, and the conversion of freshwater marsh to saline water and mangroves from 1928 to 2005.

Images from Wanless, Harold R. and B. M. Vlaswinkel 2005. "Coastal landscape and channel evolution affecting critical habitats at Cape Sable, Everglades National Park, Florida." Report to Everglades National Park.


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