Estuaries - Where a river meets the sea.

What is an estuary?

Types of Estuaries

Estuaries can be classified by the geological features that make them up.

• Coastal
• Tectonic
• Bar Built
• Fjord

• Salt wedge - found at mouths of large rivers (e.g., Mississippi), the large fresh water influx "holds back" salt water at depth creating a salt wedge, little fresh and salt water mixing
  
• Partially Mixed - deeper than well mixed, more shallow than Fjord, good fresh and salt water mixing, salinity changes both horizontally and vertically, big tidal influence
  
• Well Mixed - typically shallow with strong tidal influx of salt water, extensive mixing of salt and fresh water, uniform salinity from top to bottom, water gets saltier the closer you get to the mouth of the estuary
  
• Fjord - Deep, highly stratified water chemistry, fresh water flows out at surface, salt water flows in at depth, little mixing of fresh and salt water, anoxic conditions at depth

• To learn more about each type go to: All about Estuaries and Types of Estuaries (animated)
  

Water Chemistry in Estuaries

• Freshwater input
• Tidal range ( Link to video of tidal fluctuation in Katchemak Bay, AK)
• Bottom Topography
• Seasonal Variations
• Pollution from estuary watersheds

Habitat Types in Estuaries

• Salt marshes
• More about salt marshes
• Mangrove forests

Life in an Estuary

Etuaries are perhaps more biologically productive than any other marine ecosystem. Estuaries can also be home to a large variety of organisms.  Yet, all marine life in an estuary has to be very adaptable, particularly to the large changes in salinity.  Organisms like crabs, clams, mussels, and worms are particularly common. 

To learn more check out:
Biology of Estuaries
Salt Marsh Species

The Economics of Estuaries

Estuaries, the transition zones where rivers meet the sea, provide the focal point around which coastal communities grow. The local bay or sound nurtures a high quality of life and maintains the health and traditions of our communities. The majority of the worlds largest cities are located on estuaries.

An estuary is also a tremendous economic resource which provides jobs to coastal communities. The U.S. coasts generate more than 28 million jobs.

These jobs come from commercial and recreational fishing which alone employ 1.5 million people and contribute $111 billion to the nation's economy. And it's important to keep in mind that:

• Estuaries produce more food per acre than the most productive mid-western farmland;
• 75% of commercial species depend upon estuaries for their primary habitat, spawning grounds, and nursery areas
• 86% of recreational fishing trips occurred within 10 miles of the shoreline;
• The tourism and recreational industry growth produced by the 180 million Americans who visit estuary and coastal waters each year (1993 figures);
• In just 6 states, tourists spent over $105 billion during their 1994 visits; and
• The consumer expenditures on seafood, which totaled $38 billion in 1993.

The Roles of Estuaries in Ecological Systems

Estuaries do far more for our economy than supporting industries and providing jobs. Estuaries provide significant "services" which directly benefit Americans. For example, estuaries protect landowners from flood waters and provide important buffers that protect water quality by filtering runoff.

Beyond these measurable benefits, estuaries are at the heart of so many of our coastal communities. Without healthy estuaries, ways of life that have defined our communities for generations would disappear. The value of restoring and strengthening our estuaries can, in the end, really only be measured by the value each of us place on the quality of life we pass on to our future generations

To read more check out : http://www.oceanservice.noaa.gov/education/kits/estuaries/estuaries03_ecosystem.html

HABITAT: Tens of thousands of birds, mammals, fish, and other wildlife depend on estuaries.

NURSERY: Many marine organisms, most commercially valuable fish species included, depend on estuaries at some point during their development from egg to adult.

PRODUCTIVITY: A healthy, untended estuary produces from four to ten times the weight of organic matter produced by a cultivated corn field of the same size.

WATER FILTRATION: Water draining off the uplands carries a load of sediments and nutrients. As the water flows through salt marsh peat and the dense mesh of marsh grass blades, much of the sediment and nutrient load is filtered out. This filtration process creates cleaner and clearer water.

FLOOD CONTROL: Porous, resilient salt marsh soils and grasses absorb flood waters and dissipate storm surges. Salt marsh dominated estuaries provide natural buffers between the land and the ocean. They protect upland organisms as well as billions of dollars of human real estate.

Estuary Destruction in the United States

• Puget Sound - 73% of the original salt marshes have been destroyed;
• Narragansett Bay - 70% of salt marshes are being cut off from full tidal flow and 50% have been filled;
• San Francisco Bay - 95% of its original wetlands have been destroyed; only 300 of the original 6,000 miles of stream habitat in the Central Valley support spawning salmon;
• Galveston Bay - 85% of seagrass meadows;
• Louisiana estuaries - continue to lose 25,000 acres annually of coastal marshes, roughly the size of Washington, DC;
• Hudson-Raritan Estuary - 75% of the original tidal marshes have been destroyed in both New York and New Jersey, and 99% of New York's fresh wetlands are gone;
• Chesapeake Bay - 90% of seagrass meadows were destroyed by 1990; in 30 years (1959-89), oyster harvest fell from 25 million pounds to 1 million;
• Long Island Sound - More than 40% of the Sound's tidal wetlands have been destroyed;
• Gulf of Maine - Since 1975, developed land in the lower watershed has doubled;
• North Carolina Estuaries - The state has lost more wetlands than any other state from 1973 to 1983; and
• Tampa Bay - 80% of seagrass meadows destroyed.
  

Questions to Research:

1. What is an estuary?  Write a description of an estuary in your own words?
2. List the four types of geologial estuaries.  Based on those descriptions, what type of estuary is Cook Inlet?  What type of Estuary is Resurrection Bay (Seward)?
3. Take a virtual fieldtrip to the Providence River Estuary.  Click on the link for the Pomham Rocks site and create a graph (using three colors) or three graphs (using one color) comparing depth to DO (disolved oxygen), temperature, and salinity.  You will need to click on the link for "water reading sensors."  Write a two sentence summary for each graph giving your best explanation of why these factors change with depth.  
4. Go back to the virtual fieldtrip of the Providence River Estuary.  Click on the link for South Prudence.  Follow the same instructions as in question number for.  Create and explain graphs for what happens to DO, temperature, and salinity as you go down in depth.  
5. Create a chart that compares and contrasts mud flats, mangroves, and salt marshes based on at least three characteristics.  (think about geology, biology,  locations, etc.)
6. When exposed to salt water most trees die (think of all the dead trees near Girdwood - they were killed by saltwater a influx during the 1964 earthquake). Magrove treesare different.  They thrive in the warm salt water of tropical estuaries.  As such they are increadibly important to the stability and productivity of tropical estuaries.   Explain how is it that mangrove trees thrive in soils that are very low in oxygen and inundated with salt.
7. Describe what physical factors create a salt marsh.
8. Explain three reasons why are estuaries so economically important.
9. Based on what you have learned about ecological role of estuaries explain why there has been a big push since Hurricane Katrina to re-build the estuaries and wetlands along the coast of Louisiana.  
10. In our coastal states, more than half (roughly 55 million acres) of wetlands have been destroyed. Because of the on going threats discussed above, restoration has been a priority. Explain what the National Estuarine Research Reserve System (NERRS) is and the goal of the Estuary Restoration Act (ERA).