Focusing On The Conservation of Ecosystems, Habitats & Wildlife



FYA – For Your Awareness

Estuaries are water habitats rich in biodiversity. Ur, the oldest known population in the world settled near an estuary of the Euphrates River and Persian Gulf in 3800 BC.

The Chesapeake Bay in the U.S. is one of the largest estuaries in the country. It occupies over 100,000 miles in the District of Columbia and New York, Pennsylvania, Delaware, Maryland, West Virginia, and Virginia. Over 150 streams and rivers drain into the 188 mile long Chesapeake Bay.

What is an Estuary?

Estuaries are partially enclosed bodies of water, found along the coast where fresh water from rivers mixes with the salt water from the ocean and includes bays, lagoons, sounds and sloughs. Most estuaries are adjacent to other bodies of water, wetlands, lakes, rivers, and oceans. An estuary and the land surrounding it create a transition between the land and sea, fresh water and salt water. Although they are subject to tides their location near land acts as a barrier from the full force of the ocean, wind, and waves.

Water continuously circulates through an estuary either by the tides from the ocean or the flow from the mouth of the river. in the case of fresh water. Water levels and salinity fluctuate with the flow of water through the estuary.

Estuaries are teeming with life and offer a variety of habitats, some of which are shallow open waters; marshes, both freshwater and salt; swamps; sandy beaches; mud and sand flats; rocky shores; oyster reefs; mangrove forests; river deltas; tidal pools; sea grass; kelp beds, and wooded swamps. While most estuaries involve fresh and salt water, there are some cases of fresh water estuaries.

Freshwater estuaries are not located near oceans and are caused when rivers flow into lakes. While they are not brackish, they contain a distinct mix of lake and river water. Even though they aren’t affected by tides there can be standing waves, called seiches. An example of a fresh water estuary is the Great Lakes in the U.S. and Canada.

There are four major types of estuaries: coastal plain, bar-built, tectonic, and fjords, as determined by how they were formed.

  1. Coastal plain estuary is created by a rise in sea level filling an existing river valley. An example is the Chesapeake Bay, the United States largest estuary.
  2. Tectonic estuary is caused by geologic activity, from shifts and rifts in the earth’s crust. San Francisco Bay in California is an example of this type of estuary.
  3. Bar-built estuary is a body of water (lagoon or bay) that is protected from the ocean by a barrier island or sand bar. An example is the Outer Banks in North Carolina and Virginia that create this type of estuary.
  4. Fjord estuary is formed from glaciers carving out a steep valley. When the glacier recedes the ocean fills the existing space. Washington’s Puget Sound is an example of fjord estuaries: they are also found in Alaska and Scandinavia.

Estuaries are habitats with a mix of both land and marine life, and animals. Some of which include: mammals, shore birds, fish, reptiles, crab, lobster, clams, and worms. Birds thrive in estuaries because of the fish, worms, crabs, and clams on which they feed. Estuaries are rich in nutrients from decomposing plants, river sediment, and mud which support marine and plant life.

Where are Estuaries located?

Estuaries are located mostly near coastlines (except in the case of fresh water estuaries) throughout the world. They can exist in all climates and continents that contain rivers. Due to the variances in geology, water flow, and location, estuaries can exhibit very different characteristics and host distinct land, marine and plant species.

Why are Estuaries important to protect?

Estuaries are important to protect because of their interconnection with other biomes, including wetlands, oceans, lakes, forests, and grasslands, as well as with human communities. Not only are estuaries habitats for unique plant and animal species but they are a safe environment for small fish, shellfish, migrating birds, and coastal shore animals to rest and/or spawn. In the U.S., estuaries are nurseries to over 75% of all fish and shellfish harvested.  Estuaries help to maintain fish populations in the ocean and many populations are dependent on fish for their survival and food source. Estuaries are a source of oxygen, through photosynthesis, most of which takes place in water. Without estuaries there might not be enough oxygen for humans to breathe.

Estuaries perform a vital role in filtering small amounts of pollution and run off from the environment. They also protect land from huge surges in the oceans caused by storms and tsunamis. Estuaries are a source for recreational opportunities to hike, swim, sail, fish, and bird watch.

Another reason estuaries are important to protect is over half of the U.S. population lives in coastal areas, including along the shores of estuaries. Coastal watershed counties provided 69 million jobs and contributed $7.9 trillion to the Gross Domestic Product in 2007.

When are Estuaries under threat?

Estuaries are threatened for many reasons. As a popular location for homes and communities, land reclamation is a big threat. Estuaries are filled in for housing and industry, destroying the fragile balance and habitat for many living species of plants, birds and animals. In highly dense urban populations such as Jakarta, Indonesia, fish populations have decreased and the local fishing industry has suffered.

Because estuaries form a natural barrier from the ocean, their disappearance results in more flooding. Coastal communities lose their buffer, causing erosion, and making them more susceptible to tsunamis and hurricanes.

Another threat to estuaries is pollution caused by garbage, oil spills, sewage and other waste, as well as run-off from agricultural chemicals. When pollutants get into the rivers it endangers the bird, animal, and plant species dependent on this habitat. This happens when the chemicals overwhelm the species that filter out pollution and change the pH of the water.  For example, oysters, which act as a filter to screen out harmful chemicals can be placed in jeopardy by too many chemicals and can’t do their job. Similarly algae also filters out toxins but can rot and die when there is too much pollution. Fish that fed on these food sources won’t have anything to eat. Changes in pH disrupt the symbiotic relationships between plants and animals leading to their death.

Overfishing also impacts estuaries by disrupting the food chain dynamics. With the loss of certain species of fish, those species that relied on them as a food source must find another food source or die, which has a negative impact on the entire ecosystem, not to mention eliminating a food source for humans.

Who is protecting Estuaries?

NOAA’s National Estuarine Research Reserve System (NERRS) is a network of 28 estuarine reserves across the U.S. for long-term research, education and stewardship. It preserves more than one million acres of protected areas, covering estuarine land and water. These sites provide essential habitats for wildlife; offer educational opportunities for students, teachers and the public; and serve as living laboratories for scientists.

Restore America’s Estuaries is an alliance of eleven community conservation organizations with a mission to preserve, protect, and restore estuaries in the U.S.

The Association of National Estuary Programs (ANEP) is a nonprofit organization dedicated to the preservation and restoration of our nation’s bays and estuaries. They have over 28 programs to protect and restore U.S. estuaries that have been determined to be of significant importance to protect.

How can we protect Estuaries?

You can protect estuaries by donating time and money to support organizations that protect estuarine environments. If you live near an estuary, donate time toward clean up activities and/ or educate the public about the importance of estuaries. Purchase and use only chemicals and pesticides that aren’t harmful to the environment. Do not dispose of paints, chemicals, fertilizers or pesticides into the drain, sink, or toilet. Locate approved disposal locations for hazardous substances and rid your home or office of these toxic chemicals.