Estuaries
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Estuaries. Form where river meets the sea Regions of constant environmental change Importance to marine ecosystems Organic material enriches ocean waters Protection from predators (ex: juvenile fish) Support many commercially important animals that humans rely on for food Fish nurseries

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  • Form where river meets the sea

  • Regions of constant environmental change

  • Importance to marine ecosystems

    • Organic material enriches ocean waters

    • Protection from predators (ex: juvenile fish)

    • Support many commercially important animals that humans rely on for food

    • Fish nurseries

  • Fragile habitats

    • Pollution

    • Damage by dams Block freshwater supply


Physical characteristics of estuaries

Embayment: coastal area partially cut off from the rest of the sea

Freshwater mixes with saltwater to form an estuary

Physical Characteristics of Estuaries


Types of estuaries
Types of Estuaries the sea

  • Coastal plain (drowned river valley)

    • Form between glacial periods

    • Form when rising water levels from melting glaciers flood coastal plains and low-lying rivers


Types of estuaries1
Types of Estuaries the sea

  • Tectonic

    • Earthquakes caused land to sink, allowing seawater to cover it


Types of estuaries2
Types of Estuaries the sea

  • Fjord

    • Form when glaciers carve large valleys in coastal areas

      • Filled with water after glaciers retreated


Types of estuaries3
Types of Estuaries the sea

  • Bar-built

    • Form when geographic barriers form a wall between freshwater and saltwater


Salinity and mixing patterns
Salinity and Mixing Patterns the sea

  • Salinity varies vertically and horizontally

    • Least salty near the mouth of the river

  • Freshwater flows over the seawater

  • Surface water is less dense and flows out to sea

  • Denser saltwater from ocean moves into estuary along the bottom

    • Called positive estuary

  • Negative estuary  lose more water through evaporation than the river is able to replace

    • Low in productivity (nutrient poor)


  • Well-mixed estuary

    • River flow is low and tidal currents play major role in water circulation


  • Temperature

    • Changes rapidly with air temperature changes

    • Estuaries are heated by the sun


Estuarine productivity
Estuarine Productivity the sea

  • High because of freshwater and saltwater mixing

  • Silt and clay deposits absorb any excess nutrients from surrounding water

    • Release back into water when nutrients are in short supply

  • Filter feeders remove more phytoplankton

    • Excess phytoplankton eliminated as pseudofeces

      • Large, semisolid particles


Life in an estuary
Life in an Estuary the sea

  • Fewer species

    • Less competition for food and space

  • Feed on a variety of foods


  • Maintaining osmotic balance the sea

    • Have body fluids with same concentration of salts as seawater

      • Isosmotic to surrounding water

      • Have tissues and cells that tolerate dilution (osmoconformers) or maintain optimal salt concentration in their tissues (osmoregulators)


Estuarine communities
Estuarine Communities the sea

  • Many are euryhaline species

    • Can tolerate a broad salinity range

  • Oyster reefs  oysters growing on the shells of previous generations

  • Mud flats  contain rich deposits of organic material with small inorganic sediment grains


  • Seagrass the sea meadows  extract nutrients from sediments

  • Salt marsh community

    • Temperate and subarctic regions

    • Low and high marsh regions

  • Mangrove communities

    • Tropical regions

    • Little wave action

      • Sediments accumulate that lack oxygen


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