What is an Estuary?

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What is an Estuary?

• By Ms. Aldridge

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• An estuary is the thin zone along a coastline
  (such as bays, lagoons, sounds or sloughs) where
  freshwater systems and rivers meet, and mix with
  a salty ocean, becoming brackish. 

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Freshwater estuary

• Sometimes, freshwater from rivers mixes
  with large freshwater bodies creating a
  "freshwater estuary, such as the Great Lakes in
  the northern United States

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Types

• The 5 major types of estuaries are coastal plain,
  bar-built, delta system, tectonic, and fjords. 
• Estuaries are unique places that are valuable to
  the environment and to society.

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• Estuaries are typically classified by their
  existing geology or their geologic origins (in
  other words, how they were formed).

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Coastal Plain

• Millions of years ago, as ancient glaciers
  melted, some coastal streams and rivers became
  covered with water as sea levels rose. The
  Chesapeake Bay in Maryland and Narragansett Bay
  in Rhode Island are examples of coastal plain
  estuaries that were once river valleys.

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Bar-built

• Sandbars or barrier islands built up by ocean
  currents and waves in coastal areas created a
  protected area fed by small streams or rivers.
  The barrier islands off the Atlantic coastline of
  North Carolina are enclosed bar-built estuaries.

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Delta system

• Deltas are formed at the mouths of large
  rivers from sediment and silt depositing instead
  of being washed away by currents and waves. When
  the river flow is restricted by the delta, an
  estuary may form. The Mississippi River in
  Louisiana are examples of delta systems.

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Tectonic

• Tectonic estuaries were created when a major
  crack or a large land sink in the Earth, often
  caused by earthquakes, produced a basin below sea
  level that fills with water. These types of
  estuaries usually occur along fault lines. San
  Francisco Bay in California is an example of an
  estuary created by tectonics.

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Fjords

• Advancing glaciers ground out long, narrow
  valleys with steep sides. Then when glaciers
  melted, seawater flooded in. Glacier Bay in
  Alaska is an example of a fjord.

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• Each estuary can make up an individual
  ecosystem, estuaries are also interconnected with
  other surrounding environments (oceans, lakes,
  forests, grassy plains) and nearby human
  communities. 

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• Estuaries are constantly changing. Some
  animals and plants specialize in, or adapt to,
  living in the unique conditions of estuaries. 

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• Estuaries vary widely around the world.
  Earths changing geology, flowing water and
  different weather patterns help create many
  diverse types of habitats.

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• Rivers provide nutrients, organic matter, and
  sediments to estuaries. Rivers flow downstream
  delivering fresh water from streams, small rocks
  and silt, and leaves and other vegetation debris.
  Nutrients support life in the estuary. 

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• Estuaries can filter small amounts of
  pollutants and runoff. Vegetation helps filter
  and trap silt. However, too much nutrient or
  sediment input will create an unbalanced
  situation causing the health of the ecosystem to
  decline.

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• Estuaries act like huge sponges, buffering and
  protecting upland areas from crashing waves and
  storms and preventing soil erosion. They soak up
  excess water from floods and stormy tidal surges
  driven into shore from strong winds. 

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• Estuaries provide a safe haven and protective
  nursery for small fish, shellfish, migrating
  birds, and coastal shore animals. In the U.S.,
  estuaries are nurseries to over 75 of all fish
  and shellfish harvested.

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• People enjoy living near estuaries and the
  surrounding coastline. They sail, fish, hike,
  swim, and enjoy bird watching. An estuary is
  often the center of a coastal community.

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Effects of humans

• Anthropogenic(resulting from the influence of
  humans on the natural world) disturbances to
  estuaries include coastal development,
  introduction of invasive species, pollution via
  runoff, over fishing, dredging and filling, dams
  and global climate change.

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Coastal Development

• Hard surface can no longer absorb water or
  provide shelter or food for the animals and
  plants that exist in coastal regions.

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Invasive Species

• Purple loosestrife, nutria, hydrilla,
  snakehead fish, green crabs, and zebra mussels
  are just a few invasive species
• introduced by humans through dumping of
  aquaria containing non-native fish. Many exotic
  species compete for food and shelter, prey on na
  tive species or push native species out of their
  natural habitat.

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Pollution Via Runoff

• Water is always moving! Water runs downstream
  or through the ground from cities, farms and
  factories, this can carry many things harmful to
  estuaries such as excess nutrients, raw sewage
  and manure and chemical waste.

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Over Fishing

• Over fishing reduces the number of organisms
  in that population and, can have a negative
  effect the local food web, in turn effecting
  other species.

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Dredging and Filling

• Filling and draining of wetlands, and
  dredging deep navigation channels through
  estuaries and wetlands ultimately destroys and
  damages habitat. They also change water and
  sediment flow.

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Dams

• Changing river water flow can restrict
  sediment deposits and nutrient availability
  downstream, fish migration, and can increase
  saltwater into underground water tables.

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Global Climate Change

• Scientists are confident that the Earths
  climate has had change over the past 1,000
  years. Changes in temperature of the air and
  water, increases in sea level, more frequent and
  intense tropical storms, and changes in coastal
  currents, all of these changes can cause change!

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• Enjoy
• your
• trip
• to
• the
• Marine
• Science
• Station!