This Month in Science: Carolina Bays

If you have ever been to Jones Lake, White Lake, or Lake Waccamaw, you have been to a Carolina bay. Carolina bays are shallow elliptical depressions that have a northwest to southeast orientation and a tall rim of white sand along the southeastern edge. They range in length from a few hundred feet to over six miles—Lake Waccamaw being one of the largest1. As many as 500,000 of them exist, and some estimates put up to 80 percent in the Cape Fear Region2. While their origins are shrouded in mystery, Carolina bays display a range of environments that provide habitat to a richly biodiverse ecosystem.

The name “Carolina bay” is a bit of a misnomer. North and South Carolina have the highest density of these oval-shaped depressions, but you can find them as far south as Florida and as far north as New Jersey2. The term “bay” refers to the bay trees that surround the shore and grow alongside the wetland depressions4. Researchers estimate that Carolina bays formed anywhere between 100,000 to 30,000 years ago; however, they weren’t discovered until the 1930s when aerial photography came into use for surveying farmland4. From the air, it was easy to see the landscape peppered with the characteristic shape. From the ground, it is more difficult to identify a Carolina bay, in part, due to the wide variety in their appearance. Some are lakes, some are dry year round, and some have both wet and dry periods, depending upon rainfall5. Most depressions depend exclusively on rain water, but some, like White Lake, are fed by underwater springs6.

Carolina bays are host to a range of rare plant and animal species. The boggy wetland nature of many bays provides the ideal environment for multiple types of carnivorous plants, including flytraps, bladderworts, sundews, and pitcher plants2. Cypress, black gum, sweet gum, and bay trees, water lilies, and sedges represent a sampling of plants that thrive in Carolina bays. Some bays experience seasonal periods of dryness. Because of these dry spells, there are bays with no predatory fish species which allows aquatic invertebrates to thrive6. The cyclical wet and dry periods are also ideal for amphibious creatures, allowing them to breed during the wet phase and mature during the dry phase. The environmental variation between bays means that no two bays are alike. Each Carolina bay has its own individualized and diverse ecosystem7—there are at least seven aquatic species that exist only in and around Lake Waccamaw8.

Many theories exist to explain the origins of Carolina bays. A few of the proposed theories include ideas that giant schools of fish created the depressions for spawning purposes, a series of meteors left the oval-shaped scars on the surface, and movement of icebergs carved them out2. The most widely accepted theory among researchers today is commonly referred to as the oriented lake theory. It proposes that when the oceans that once covered this region retreated, pools of water remained in low spots. Over time, strong winds from the north-northeast elongated these pools of water into the oval shapes we see today7.

Carolina bays tend to naturally decrease in size over time. The bay trees that root along the shore allow soil and dead vegetation to build up along the shoreline, slowly filling in the lake. When it becomes completely filled in, it becomes a boggy wetland called a pocosin1. Nature isn’t the only way for a wetland Carolina bay to become dry. It is estimated that 79 percent of Carolina bays in North and South Carolina have been destroyed or altered by human action7. Many were drained to create farmland or provide a foundation for construction. The destruction and alteration of these bays disrupts habitats and breeding grounds to the species that live in them.

To preserve the unique ecosystems and endemic species—native to only that region—of Carolina bays, many are now protected. The Nature Conservancy protects several Carolina bays in North Carolina, including Antioch Bay and Hamby’s Bay7. There are over 900 Carolina bays in Bladen County alone, so if you’re interested in seeing one for yourself, Bladen is the place to go. You can also check out the exhibit at the Jones Lake State Park Visitor Center to take a deeper dive into Carolina bays.

References:

      1. http://lakelevel.web.unc.edu/what-are-carolina-bays/
      2. Krajick, Kevin The Riddle of the Carolina Bays Smithsonian Magazine September 1997
      3. Zgonnik et al. Evidence for natural molecular hydrogen seepage associated with Carolina bays (surficial, ovoid depression on the Atlantic Coastal Plain, Province of the USA) Progress in Earth and Planetary Science October 2015
      4. https://www.coastalreview.org/2013/08/the-fiery-origins-of-carolina-bays/
      5. http://archive-srel.uga.edu/outreach/factsheet/carolinabays.html
      6. Sharitz, Rebecca R. Carolina bay wetlands: Unique habitats of the southeastern United States Wetlands September 2003, Vol 23, Issue 3, pp550-562
      7. https://ncseagrant.ncsu.edu/coastwatch/previous-issues/2015-2/autumn-2015/carolina-bays-another-mans-treasure/
      8. http://lakelevel.web.unc.edu/lake-waccamaw-a-north-carolina-treasure/

 

Previous Columns

October 2019: The Longleaf Pine
September 2019: Jellyfish
August 2019: What’s in Your Childhood Chemistry Set?
July 2019: What Happened to the Dinosaurs?
June 2019: Hurricane Season
April 2019: Quantum Levitation
March 2019: Venus Flytrap
February 2019: A Shifting Magnetic Field
January 2019: Giant Ground Sloth
December: Snowflakes
November: Citizen Science
October: Parker Solar Probe Voyaging to the Sun
August: Sea Turtle Season
July: Plastic Free July
June 2018: All About Alligators


Satellite image of Carolina bays in Bladen County, NC.
Source: http://lakelevel.web.unc.edu/what-are-carolina-bays/

Distribution of Carolina bays in North Carolina. Carolina bays are outlined in orange.
Source: Zgonnik et al.

Suggs Mill Pond, also known as Horseshoe lake, is a partially filled in Carolina bay.
Source: NC Wetlands

Infographic depicting how a bay lake disappears over time.
Credit: Jones Lake State Park

Antioch bay is a Carolina bay filled in by cypress and blackgum trees that periodically floods.
Image credit: Ken Taylor/Wildlife Images
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