ESTUARIES

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ESTUARIES

• GEOL 1033
• (Lesson 32 36)
• ppt file 103-30

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ESTUARIES, BAYS, LAGOONS

• Bays a general term for a coastal embayment.
• Estuary a bay that is semi-enclosed, has
  fresh-water input from a river(s), experiences
  tides.
• Lagoon semi-enclosed bay with little or no
  river input reduced to essentially no tides.

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ESTUARIES

• Estuaries have
• Tidal influences
• Tidal flats
• Salt marshes
• Wave action
• River influences (freshwater, sediment input,
  nutrients)
• Sediment accumulation is significant
• Estuaries are young features
• Because they tend to fill with sediments
• They are said to be sediment sinks

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ESTUARIES

• Distribution common worldwide
• Size varies
• Depth varies from shallow (coastal plains) to
  deep (fjord)
• biological significance
• highest productivity in the world!
• nutrients from land runoff (rivers)
• shallow enough for photosynthesis
• well mixed by tides for good distribution of
  oxygen
• home of many organisms (very diverse and abundant
  life)
• nursery for many open ocean organisms, e. g.,
  shrimp, many fish.
• Processes
• tides tend to be the dominant physical
  environmental factor
• waves are locally important (especially in large
  estuaries with long fetches)
• bioturbation by invertebrates tends to homogenize
  subtidal sediments
• Sedimentation rates are significant
• Duration 100s to 1000s years, not tens of
  thousands to millions

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ORIGIN OF MOST ESTUARIES
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TECTONIC ESTUARIES

• San Francisco Bay is formed by three major
  faults. This structural bay is the site of the
  cities of Oakland and San Francisco - a recipe
  for disaster!

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FJORDS

• Fjord type estuaries were carved by glaciers that
  flowed down valleys to the sea.

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DROWNED VALLEYS

• Coastal plain river valleys are drowned by rising
  sea levels, forming estuaries.

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CONSTRUCTIONAL ESTUARIES

• Formation of an estuary behind a spit, bar or
  barrier island

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TYPES OF ESTUARIES

• a) stratified (isohalines almost horizontal)
• b) well-mixed (isohalines nearly vertical)
• c) partially mixed (isohalines oblique)

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END OF FILE
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GENERALIZED COASTAL ECOSYSTEM MODEL

• RIVERS NUTRIENTS
• SEA
• SUNLIGHT
• SEDIMENTS PRODUCERS
• CONSUMERS
• DECOMPOSERS

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