Answer – An estuary is a region where a freshwater river or stream converges with the ocean.
Explanation:
The term estuary originates from the Latin words aestus (meaning “the tide”) and aestuo (meaning “boil”). An estuary may also be called a bay, lagoon, sound, or slough. Within estuaries, the blending of salty ocean water with fresh water from rivers creates brackish water.
In general, an estuary’s water level and saltiness change with the tides and seasons. When it rains a lot, rivers flood the estuary with fresh water. In dry times, river flow slows down, making the estuary smaller and saltier. Storms can bring in salty ocean water, but natural barriers like reefs and islands protect most estuaries from strong ocean waves.
An estuary is a coastal water body where freshwater from rivers and streams meets and mixes with saltwater from the ocean Image credit: Mattole / Wikimedia Commons (licensed under CC BY-SA 3.0)
There are four main types of estuaries: the salt wedge estuary, the partially mixed estuary, the vertically homogeneous estuary, and the fjord.
Salt wedge estuary: In a salt wedge estuary, freshwater from the river flows over denser saltwater, creating a distinct wedge-shaped layering. This type is common in areas with strong river flow and minimal tidal influence. The Columbia River Estuary (United States), where the Columbia River discharges into the Pacific Ocean is an example of a salt wedge estuary.
Partially mixed estuary: Partially mixed estuaries experience moderate tidal influence, resulting in a more even mixing of freshwater and saltwater. An example of this type is the Thames estuary in the United Kingdom.
Vertically homogeneous estuary: In vertically homogeneous estuaries, tidal forces strongly mix freshwater and saltwater throughout the water column. The Delaware Bay (United States), where the Delaware River meets the Atlantic Ocean, is an example of a vertically homogeneous estuary.
Fjord estuary: Fjord estuaries are characterized by deep, glacially-carved inlets with steep sides. They exhibit strong stratification, with distinct layers of freshwater and saltwater, often leading to minimal mixing. Puget Sound is a fjord estuary in the Pacific Northwest.
On average, estuaries are biologically more productive than either the adjacent river or the sea because they have a special kind of water circulation that traps plant nutrients and stimulates primary production. In addition, they are held significant as locations for harbors and hubs of economic activity.
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