Deltas and Estuaries

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Deltas and Estuaries

• Lecture D

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Delta

• Sediment washed out of rivers protruding from
  shore.
• River dominated delta
• Wave dominated delta
• Tide dominated delta

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Delta types
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Growth of deltas
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River Dominated Delta

• Example Mississippi River
• Nile River
• Low energy coastline (low waves)
• Microtidal (low tide)
• Strong river current

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River Dominated Delta

• Delta Plain- above water
• has distributaries
• interdistributaries
• natural levees
• estuaries
• tidal flats
• salt marshes (rich in oysters, clams, and shrimp)
  
• also has the riverine and estuarine environments

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River Dominated Delta

• Delta front
• Underwater
• Where river forces (current) meets ocean forces
  (waves, tides, and currents)
• Upper front has coarse sediment
• Lower front has fine sediment

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River Dominated Delta

• Pro delta
• Largest of the three (delta plain, front, pro)
• Most uniform sediment (sediment mostly from
  suspension)
• Sediment is mainly mud
• Mississippi delta sediment has gone over the edge
  of the continental shelf
• Strong waves and currents will destroy pro delta

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Growth of a river dominated delta
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Wave Dominated Delta

• Example Sabine River (western Louisiana)
  Robinson River (NT), Richmond River (NSW),
  Gascoyne River (WA).
• High energy coastline
• Usually small river
• Sediment and sand carried away by currents
  waves
• Few interdistributary area, tidal flats, or salt
  marshes

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Tide Dominated Delta

• Low energy coastline
• Macrotidal
• Funnel shaped mouth
• Sand bars parallel to river current
• Caused by strong tidal currents
• Example Colorado River,
• Burdekin River (QLD), Limmen
• Bight River (NT), and Norman River (QLD).

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Tide dominated

• Tide-dominated deltas are characterised by
  relatively high tide energy at the mouth compared
  with wave energy, and are distinguished from
  tide-dominated estuaries by high river energy.
• Tidal energy is greatest slightly landward of the
  mouth due to constriction by the funnel shaped
  mouth.
• Wave energy is dissipated on shoals seaward of
  the mouth, and declines rapidly landwards.
• River energy remains moderate to high along the
  channel, but drops off significantly as the
  channel widens towards the mouth.

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Tide dominated
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Estuaries

• Partially enclosed bay of water with an influx of
  both freshwater from a river(s) and salt water
  from the sea. The fresh and salt waters mix
  providing an area of remarkable biological
  productivity.
• http//www.onr.navy.mil/focus/ocean/habitats/estua
  ries1.htm

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Estuaries nurseries of the sea

• Between 90 and 97 of all commercial fish caught
  in Florida live in the estuary at some time of
  their lives

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Sediment

• As sediment sinks, they are geologically
  shortlived estuaries are
• varied,
• fragile,
• nutrient rich,
• productive,
• and threatened.

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Osmoregulation Sea cucumber

• Body fluids same as sea water (35ppt)
• when in seawater (35ppt)- water out as fast as in
• If in freshwater(0 ppt)
• body fluids are still 35 ppt and water diffuses
  in
• Salts cannot diffuse out
• Fatal
• Animals cant move into fresher areas (the same
  holds true for most marine invertebrates and
  plants)

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Osmoregulation Salmon-Maintains body fluid at
18ppt

• In Sea water (35 ppt)
• Hypertonic
• Salmon loses water
• Drinks constantly
• Kidneys cannot produce urine with higher
  salinity than the body
• Special chloride cells in gills get rid of
  excess salt

• In fresh water (0 ppt)
• Hypotonic
• Salmon gains water
• No drinking
• Kidneys produce lots of dilute urine

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Oyster Osmoregulation

• Oysters can tolerate 5 ppt to 30 ppt
• Starfish and oyster drill cant take
• salinity past 18 ppt 0 ppt
• Oyster disease MSX is an 5 ppt
• unknown protozoan 10 ppt
• at 15 ppt in droughts, 15 ppt
• salinity moves up estuary 20 ppt
• and MSX moves with it 25 ppt
• destroyed oyster crop 30 ppt
• in 1957 1988 35 ppt

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Blue Crab Osmoregulation

• Low tolerance for salinity
• Males called Jimmies
• Large Jimmies prefer deeper water in tidal
  channels
• Females called Sooks
• Follow the salinity movement with seasonal
  changes
• more rain, fresh water flows farther down estuary
• less rain, saltier water higher in estuary

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estuaries

• Estuaries are partially enclosed bodies of water
  where freshwater (water without salt) meets salty
  ocean water. Bays, inlets and ocean-flooded river
  valleys are all examples of estuaries.
• Estuaries are divided into four types, depending
  on how they are formed

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1. Coastal Plain Estuaries

• formed by the sea level rising and filling an
  existing river valley
• Examples
• Chesapeake Bay in Maryland
• the harbor in Charleston, South Carolina

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2. Tectonic Estuaries

• caused by the folding or faulting of land
  surfaces.
• These estuaries are found along major fault lines
• Example San Francisco Bay area in California.

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3. Bar-built Estuaries

• form when a shallow lagoon or bay is protected
  from the ocean by a sand bar or barrier island.
• Examples of these are found along the Eastern
  Seaboard and the Gulf Coast of North America.

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4. Fjords

• U-shaped valleys formed by glacial action.
• Fjords are found in areas with long histories of
  glacier activity, like northern Europe, Alaska
  and Canada.