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Tides Create Cyclical Changes in Estuaries
Tides are necessary for healthy estuaries as they flush the systems and provide nutrients to keep the food webs functional. However, tides create constantly changing conditions of exposure to air and inundation to water.
Earth’s gravity holds our oceans and seas to its surface. At the same time, the sun and the moon’s gravity forces pull on the oceans. Water on one side of Earth is pulled toward the moon and bulges out (creating a tidal bulge). Another tidal bulge on the opposite side of Earth occurs because the water on that side, being farther away from the moon, is not pulled toward the moon as strongly as is the earth. As Earth rotates, different places on the planet’s surface experience the tidal bulge, and therefore experience changes in water levels. This daily rise and fall of the oceans are called tides.
Tides flood as the waters rise on the coast, pushing seawater into an estuary. Tides ebb and the waters flow out to sea. Tides ebb and flood on cycles over a 24-hour period. Each day, estuaries can have one or two high tides, plus one or two low tides. Animals and plants must adapt to this daily water level change, or they won’t survive. Tides are necessary for healthy estuaries as they flush the systems and provide nutrients to keep the food webs functional.
As the tide ebbs and flows, the intertidal zone is once exposed to the elements and then inundated by tidal waters. In addition to the alternating wet and dry conditions, organisms must adapt to the waves that are in constant action in this zone.
Do you think there are differences in tidal range, the change between low and high tide, around the world? In Katchemak Bay in Alaska, spring tides can have a 20-22 foot tidal range between extreme low and high tides. Grand Bay in Mississippi experiences a much lower tidal range (1- 2 feet) in the spring.
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Last Updated on: 06-23-2008
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