Nature up close: Vortex Spring
By contributing “Sunday Morning” nature videographer Judy Lehmberg:
I used to think geology was boring because it was all a bunch of rocks. However, I have come to realize just how amazing it can be that all of the continents on Earth used to be one land mass, much of North America has been covered with oceans, and the Grand Canyon is just a spectacular example of erosion.
One of the more intriguing aspects of the geological activity on Earth is karst topography. It is an area formed when soluble rocks, especially limestone, are dissolved to form caves and sinkholes.
Limestone is calcium carbonate, so it can be readily dissolved by acids. When it rains, water reacts with carbon dioxide in the air to form the weak acid, carbonic acid. Once the rainwater hits the ground, it can pick up more carbon dioxide, depending on soil type, to become even more acidic. If an area is made up of rocks such as limestone, the acidic water can flow into any cracks or fissures. That leads to the cracks widening and forming underground caves, where even more water can flow.
Over the eons, as landscapes change, water levels can rise to cause water that once flowed down to begin flowing back up. If that happens, a beautiful spring forms, such as Vortex Spring.
Vortex Spring releases about 28,000,000 gallons of water per day from a 10-foot-wide opening in limestone located near the center of its 15-foot-wide bowl pool connected to a 1,642-foot-long cave. The water is extremely clear, and is a magnet for divers and swimmers.
One of the inhabitants of Vortex Spring is freshwater eels. I’ve always been fascinated with them because until the 1920s no one was sure where they reproduced -- and because we don’t give them much respect.
Think about it: We like animals with “regulation” numbers of legs. Two or four legs are fine (humans, dogs and cats), but we aren’t too crazy about the ones with six, eight or zero legs (insects, spiders, snakes and eels). So even though they are considered a delicacy in some countries, most Americans don’t like eels.
There are a number of fish, such as salmon, who live most of their life in saltwater and return to freshwater to spawn. They are anadromous. Catadromous fish do the opposite; they spend their adult lives in freshwater and return to saltwater to spawn.
Both European and American freshwater eels spawn in the Sargasso Sea, presumably using the seaweed, sargassum, to hide in while they are very small. The trip they make to the Sargasso Sea is amazing. Some travel as many as 3,700 miles. How they are able to make that long trip remains a mystery. As they move from fresh to saltwater their digestive system disappears, their eyes get larger, their eye pigments change to better see in low, blue ocean light, and the sides of their bodies turn silvery, to make it more difficult for predators to see them.
They also have to totally change the way they maintain their water and salt balance. Animals that live in freshwater have problems retaining salt as water moves into their cells by osmosis. Animals in saltwater have the opposite problem: too much salt and not enough water. Animals that move from salt to freshwater must change from conserving water to conserving salt, and visa versa. That is a major metabolic change. Kidneys that are designed to eliminate water in freshwater must be able to conserve water and excrete salt in the ocean. A human surrounded by ocean water would die of dehydration, because osmosis would cause us to lose too much water to the ocean.
Animals and plants evolve to exist using the water available to them, from eels and sargassum in the salty Atlantic, to the freshwater plants and bluegill in Vortex Spring.
Judy Lehmberg is a former college biology teacher who now shoots nature videos.
For more info:
- Judy Lehmberg (Official site)
- Judy Lehmberg’s YouTube Channel
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