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Estuaries: One of the Most Productive Ecosystems in the World

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Ankita loves to explore various aspects of science and is passionate about writing on topics of her interest.

Chesapeake Bay

Chesapeake Bay

Why Are Estuaries Highly Productive?

Estuaries are bodies of water that are usually found where a river meets the sea. In other words, an estuary is an area where a freshwater source meets the ocean. When seawater and freshwater combine, the water becomes slightly salty, which is referred to as brackish water. An estuary may also be known as a bay, sound, lagoon, or slough.

There is a continuous circulation of water in and out of an estuary. Mouths create the largest flow of freshwater, whereas tides create the largest flow of seawater. In estuaries, salinity and water level rise and fall with the tides and seasons. During storm seasons, geographical features such as islands, mud, reefs, and sand act as barriers from strong winds and ocean waves to protect the estuaries.

There are some estuaries that are not located near oceans. These are known as freshwater estuaries and they are created when a river flows into a freshwater lake. The Great Lakes in Canada and the United States have many freshwater estuaries.

Types of Estuaries

Estuaries are categorized into four different types based on their creations. They are coastal plain estuaries, bar-built estuaries, tectonic estuaries, and fjord estuaries.

Coastal Plain Estuaries

These are created when an existing river valley is filled with seawater due to a rise in sea level. The Chesapeake Bay on the East Coast of the United States, which is known to be formed at the end of the last ice age, is an example of this kind of estuary.

Bar-Built Estuary

When a bay or lagoon is protected from the ocean by a sandbar or barrier island, it is referred to as a bar-built estuary. A series of narrow barrier islands called the Outer Banks in North Carolina and Virginia, create bar-built estuaries. The Outer Banks act as a barrier against the waves and winds brought by Atlantic Ocean hurricanes and thus protect the region’s coast. The engineers constantly monitor the sandbars of the Outer Banks for this reason.

Outer Banks

Outer Banks

Tectonic Estuaries

As the name suggests, these estuaries are created due to tectonic activity. An example of a tectonic estuary is the San Francisco Bay located in California. The complex tectonic activity in that area has created earthquakes for thousands of years.

San Francisco Bay

San Francisco Bay

Fjord Estuaries

These types of estuaries are created by glaciers. When glaciers carve out a steep, deep valley, fjord estuaries occur. Glaciers retreat and the ocean rushes to fill in the deep, narrow depression. In the U.S. state of Washington, Puget Sound is a series of fjord estuaries.

Puget Sound

Puget Sound

The Importance of Estuaries

Estuaries are a home to many plant and animal species and are considered to be one of the most productive ecosystems on earth. Many animals rely on them for food, migration stopovers and places to breed. The calm waters provide a safe area for shellfish, small fish, migrating birds and shore animals. Detritus (decomposing plant matter) provides food for many species. The waters are also rich in nutrients such as bacteria and plankton.

The high level of plant production in estuaries results in high levels of invertebrate animals and fish production. The estuarine crocodile is the largest reptile in the world. This apex predator of Southeast Asian and tropical Australian estuaries eat almost anything. This means that the estuary must support a wide variety of food webs. These crocodiles have also adapted to seasonally vanishing estuaries.

Estuaries have been always seen as harbour sites and centres of commerce. They are great sites for community living. Some of the oldest civilisations around the world have in fact flourished in estuarine environments. In addition, many estuaries are important sites for aquaculture. Modern cities like New York City, Jakarta, and Tokyo have grown around estuaries. Due to the rapid changes and developments in these cities, the estuaries around them are facing environmental risks through pollution, land reclamation and overfishing. Estuaries are irreplaceable natural resources and must be managed for the greater benefit for those who enjoy and depend on them.

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Threats to Estuaries

Land reclamation is seen as one of the major threats to estuaries, since many communities have filled in the edges of estuaries for housing and industry. Destroying them also increases the chances of floods. Estuaries act as barriers against ocean waves, which can erode the shoreline and cause major damage to homes and businesses.

Studies have found that Jakarta is particularly at risk for tsunami damage since the region experiences frequent earthquakes. The Hudson-Raritan Estuary is found to be one of the most polluted and most trafficked estuaries in the world. Strict regulations and community activities are working today to restore and protect this estuary. Restoration of oyster beds is also an important part of many projects in recent years.

Another threat to the estuaries is overfishing. Pacific bluefin tuna, which once used to swim in the Tokyo Bay, are now rarely seen because of overfishing. Japanese scientists, however, have established a tuna fish farming technique successfully. Nowadays, many environmental groups struggle to promote sustainable development in estuaries.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.


Ankita B (author) on October 07, 2020:

It is true what you have written, Denise. Thank you for your insightful comments. I appreciate it very much.

Denise McGill from Fresno CA on October 07, 2020:

It is a dilemma. How do you convince people that nature had a better way? It seems we humans never can let well enough alone.



Ankita B (author) on October 07, 2020:

Thank you very much Pamela for your encouraging words. I am so glad that you enjoyed reading this article and truly appreciate your generous comments.

Pamela Oglesby from Sunny Florida on October 07, 2020:

This is a very interesting article and I learned a lot. You see to write many uniquely different articles that I really enjoy, Ankita. I liked your pictures as well.

Ankita B (author) on October 07, 2020:

Thank you so much Prithviraj for reading and commenting. I truly appreciate your kind comments.

Ankita B (author) on October 07, 2020:

Thank you for your lovely and insightful comments, Brenda. I am delighted to know that you enjoyed reading this article and found it informative.

Prithviraj Shirole from India on October 07, 2020:

Thanks for sharing an informative article on Estuaries, Ankita. The photos are also lovely.

BRENDA ARLEDGE from Washington Court House on October 06, 2020:

Alot of information here I did not know. I don't live near an ocean or a bay so I guess I hadn't thought about it much.

The water constantly moving & is salty where they meet.

I only knew that oceans were salty. I certainly didn't realize there were different types as well.

I don't believe I would live close to the border on these. Tsunami's would scare me.

Thanks for sharing.

Ankita B (author) on October 05, 2020:

I am pleased to know that you enjoyed reading my article and found it informative. Thank you so much Linda for your kind comments.

Linda Crampton from British Columbia, Canada on October 05, 2020:

Thank you for sharing the interesting information, Ankita. Estuaries are important places. I'm glad that I've read facts about them in your article.

Ankita B (author) on October 05, 2020:

Thank you very much Rosina for your encouraging words. I am so glad that you enjoyed reading this article.

Rosina S Khan on October 05, 2020:

This a good and well-informed article about estuaries- their types, importance, and threats along with appropriate and lovely illustrations. A splendid article, Ankita!

Ankita B (author) on October 04, 2020:

True Jay C. Population is one of the major causes. Thank you for your insightful comments. I appreciate it very much.

Ankita B (author) on October 04, 2020:

Thank you very much James. I appreciate your comments. The joke is indeed good, lol. I am glad you found this informative.

Jay C OBrien from Houston, TX USA on October 04, 2020:

We must protect our earth from pollution. Mankind must learn to controll their population to a sustainable level. Family Planning is needed.

James C Moore from Joliet, IL on October 04, 2020:

I've heard the term estuary before but didn't know what made these distinct from other bodies of water. Good info.

I have an estuary joke:

What is New York City's loudest body of water?...

The Long Island Sound

Ankita B (author) on October 04, 2020:

Thank you Millicent. I appreciate your generous comments very much.

Millicent Okello from Nairobi, Kenya on October 04, 2020:

Hello Ankita.

Wow. For the first time in my life i am learning about the estuaries. I find it even more interesting to know that During storm seasons, geographical features such as islands, mud, reefs and sand act as barriers from strong wind and ocean waves to protect the estuaries.

Thanks for this informative article Ankita.

Ankita B (author) on October 04, 2020:

Thank you Farah for your kind comments which I always appreciate. Take care.

Ankita B (author) on October 04, 2020:

Thank you Raymond for your comments which I appreciate. I am glad you found this article interesting. It is sad to know about the huge estuary been left with only smaller fragments.

Farah N Huq from Dhaka, Bangladesh on October 04, 2020:

Read a bit about estuary while helping my son with his school lesson. Found this very informative.

Raymond Philippe from The Netherlands on October 04, 2020:

An interesting read. We had a huge estuary in the Netherlands. But after building the Delta Works we only have two smaller ones left.

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