EstuariesEstuaries

By Dan LawsonBy Dan Lawson

What is an estuary?What is an estuary?

An estuary is a coastal body of water An estuary is a coastal body of water which is openly connecting a which is openly connecting a freshwater stream with a saltwater freshwater stream with a saltwater environment such as the ocean.environment such as the ocean.

LocationLocation

Estuaries are found all Estuaries are found all over the world in over the world in coastal areas. They coastal areas. They can also be called can also be called bays, lagoons, bays, lagoons, harbors, or sounds. harbors, or sounds. They are only true They are only true estuaries, however, estuaries, however, when there is both salt when there is both salt and fresh water and fresh water present.present.

Types of EstuariesTypes of Estuaries

Drowned River Valleys-Drowned River Valleys- Many estuaries of this type Many estuaries of this type

were formed between 15,000-were formed between 15,000-6,000 years ago.6,000 years ago.

They were formed when the They were formed when the end of the last glaciation end of the last glaciation period caused sea level to period caused sea level to rise 100-130m.rise 100-130m.

Drowned river valleys are Drowned river valleys are typically wide and shallow, typically wide and shallow, rarely exceeding 30m in rarely exceeding 30m in depth.depth.

Examples include Chesapeake Examples include Chesapeake Bay (the largest estuary in the Bay (the largest estuary in the United States) and Delaware United States) and Delaware Bay. Bay.

Chesapeake Bay from Satellite

Types of EstuariesTypes of Estuaries

Lagoon-Type-Lagoon-Type- Semi isolated from the Semi isolated from the

ocean by barrier islands, ocean by barrier islands, which are narrow strips of which are narrow strips of land that only allow water land that only allow water to flow through small to flow through small inlets.inlets.

A good example is Pamlico A good example is Pamlico Sound, the largest lagoon Sound, the largest lagoon on the US east coast. on the US east coast. Located in North Carolina, Located in North Carolina, it is separated from the it is separated from the Atlantic by the Outer Atlantic by the Outer Banks.Banks.

Types of EstuariesTypes of Estuaries

Fjord Type – Fjord Type – Found in valleys that Found in valleys that

are deeply eroded are deeply eroded from glacial activity.from glacial activity.

Very narrow and deepVery narrow and deep Can exceed 300m in Can exceed 300m in

depthdepth Examples include Examples include

Alaskan coast, Puget Alaskan coast, Puget Sound region of Sound region of Washington, areas in Washington, areas in Norway, and New Norway, and New Zealand.Zealand.

Organisms Found in Organisms Found in EstuariesEstuaries

Estuaries are among the most heavily Estuaries are among the most heavily populated areas in the world, with almost populated areas in the world, with almost 60% of species being found in estuaries and 60% of species being found in estuaries and coastal areas. In order to survive in the coastal areas. In order to survive in the water found in an estuary, organisms must water found in an estuary, organisms must be euryhaline (able to adapt to a wide range be euryhaline (able to adapt to a wide range of salinity)of salinity)

Some examples of organisms found in Some examples of organisms found in estuaries are eels, horseshoe crabs, oysters, estuaries are eels, horseshoe crabs, oysters, seahorses, blue crabs, bull sharks, salmon, seahorses, blue crabs, bull sharks, salmon, striped bass, and sturgeon.striped bass, and sturgeon.

Threats to EstuariesThreats to Estuaries

Estuaries are threatened by both human Estuaries are threatened by both human and non-human environmental impacts.and non-human environmental impacts.

Some of the main natural threats include Some of the main natural threats include sediment deposition which can clog feeding sediment deposition which can clog feeding and breathing holes of certain species. and breathing holes of certain species. Sediment also works to fill in estuaries, Sediment also works to fill in estuaries, decreasing space for organisms to live. decreasing space for organisms to live.

Another problem is rapidly changing salinity Another problem is rapidly changing salinity levels, which create a harsh environment levels, which create a harsh environment for organisms in the estuary.for organisms in the estuary.

Threats to EstuariesThreats to Estuaries

Human Impacts – Human Impacts – Of the 32 largest cities in the world, 22 are located on Of the 32 largest cities in the world, 22 are located on

estuaries.estuaries. Pollution from upstream travels down the river and affects Pollution from upstream travels down the river and affects

the estuary environment.the estuary environment. Bioaccumulation can occur which is when pollutants such Bioaccumulation can occur which is when pollutants such

as Mercury or pesticides build up in the tissues of marine as Mercury or pesticides build up in the tissues of marine animals, making them unsafe for consumption.animals, making them unsafe for consumption.

Another threat to estuary life is overfishing. The Another threat to estuary life is overfishing. The Chesapeake Bay oyster population used to be huge, but has Chesapeake Bay oyster population used to be huge, but has almost been wiped out due to overfishing. This greatly almost been wiped out due to overfishing. This greatly reduces the ability of oysters to help filter the water.reduces the ability of oysters to help filter the water.

It has been said that the oysters used to filter excess It has been said that the oysters used to filter excess nutrients from all of the water in the estuary in 3-4 days. nutrients from all of the water in the estuary in 3-4 days. Now the process takes almost a year.Now the process takes almost a year.

In ConclusionIn Conclusion

Estuaries are a vital part of the ecosystem. Estuaries are a vital part of the ecosystem. The huge amount of organisms living in The huge amount of organisms living in this environment are essential to the well this environment are essential to the well being of other environments such as the being of other environments such as the ocean and rivers.ocean and rivers.

Estuaries are essential to anadromous Estuaries are essential to anadromous animals that travel up stream to spawn. animals that travel up stream to spawn.

They also act as the filters of the water They also act as the filters of the water travelling downstream towards the ocean.travelling downstream towards the ocean.

Without estuaries, many species of plants Without estuaries, many species of plants and animals would not be able to survive.and animals would not be able to survive.