Chapter 12 Estuaries Where Rivers meet the Sea
Chapter 12EstuariesWhere Rivers meet the Sea
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Estuaries
• Semi-enclosed areas where fresh water and seawater meet and mix.
• Interaction of land and sea!
• Some of the most productive environments on earth!
• Most affected by humans!– Harbors– Cities
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Value of Estuaries
• Protected fertile habitat – Home for many!
• Vital breeding and feeding grounds
• Cities built near estuaries because of great fishing. (shrimp and crab)
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Cape Hatteras EstuaryIn N. Carolina
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Milford Sound in New Zealand is a fjord – a finger-like inlet surrounded by sheer walls with a shallow entrance and deep basin
resulting in stagnant, oxygen-depleted deep water.
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4 Types of Estuaries
• Drowned River Valleys or Coastal Plain – Sea invaded lowlands– Most common– Chesapeake Bay
• Bar-built– Sand builds up to form sand bars and barriers– Along Texas coast of Gulf of Mexico
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4 Types of Estuaries
• Tectonic– Land sinks or earth moves
• Fjords – Glacier Carved– Retreating glaciers cut deep valleys that are
partially submerged– Common near Alaska
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Isohaline are the same salt content water. How many are there?
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High Tide
Low Tide
The Salt wedge moves in and out with the tide
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Physical Characteristics of Estuaries
• Salinity in a salt wedge
• Substrate– Rivers carry nutrients into estuary by size and
weight. Which travels farther?– Mud = silt and clay high in nutrients– Anoxic = low oxygen in mud b/c bacteria
respiration.– Anaerobic bacteria thrive in mud. Why?
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Physical Characteristics of Estuaries
• Water temp varies. Why? When? So?
• Exposed organisms during low tides.– Sun, Drying out, Predation
• Low water clarity causes what problem?
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Types of species living in an idealized estuary in relation to salinity. The width of the bars = relative numbers of species
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The body fluids of estuarine animals responds in various ways to the salinity of the water. Osmoregulator = blood salinity stays the same. Osmoconformer=blood salinity will change with the water salinity.
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Look at the shallow roots of
this mangrove tree reaching above the
mud to get oxygen.
Why does mud not have much oxygen
in it?
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Cordgrass is an important component of salt water marshes
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Pickle Weed is a common succulent plant in salt marshes around the world.
19The Atlantic menhaden is an important commercial fish spawn
offshore and larvae drift with tides into the estuary to grow.
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The California horn snail is abundant on
mudflats
21Mudflat animals in temperate estuaries
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Fiddler on the Mud
What is this behavior for?
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The daily tides play a crucial role in salt marshes.
They help circulate detritus and nutrients and
expose mudflat organisms to predation by
shorebirds and other animals
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A salt marsh near Atlantic Beach, NC. Many of these types of marshes have been filled in and destroyed.
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A mudskipper from the mudflats of a mangrove forest in New Guinea. Its eyes can see in air.
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An Oyster reef formed by the eastern oyster near Beaufort, NC are exposed at low tide.
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