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ESTUARIES

ESTUARIES. Estuary: Partly enclosed body of water One or more rivers or streams flowing through it Free connection to open ocean Therefore, is subject to both marine and river influences. DROWNED RIVER VALLEYS

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ESTUARIES

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  1. ESTUARIES

  2. Estuary: • Partly enclosed body of water • One or more rivers or streams flowing through it • Free connection to open ocean • Therefore, is subject to both marine and river influences

  3. DROWNED RIVER VALLEYS • Formed 15,000 – 6,000 years ago by a eustatic rise in sea levels and general subsidence of coastal regions • Found on low, wide coastlines, with wide coastal plains • Very shallow (rarely more than 30 m deep) • Examples: Chesapeake Bay, Delaware Bay FJORD-TYPE • Found in eroded valleys formed by glaciers • Steep sides, rock bottoms, very deep (over 300 m) and narrow • Tides only affect the surface waters, deep water remains stagnant for long periods of time

  4. BAR-BUILT • Semi-isolated by barrier beaches • Usually on tectonically stable edges of continents with active costal deposition of sediments • Long and parallel to the shore • Depth is 5m – 10m • TECHTONICALY PRODUCED • Formed by subsidence , faulting, volcanoes, and landslides • There are very few in the world: one example is San Francisco bay

  5. ESTUARIAN WATER CICUALTION • Lighter, less dense water flows near the surface, while denser flows inward from the sea near the bottom • Because of this, salinity can vary from 0% to 34% • Flushing time: time it takes all the water to in an estuary to completely cycle

  6. ESTUARIEN WATER CIRCUALTION • Residence time: average amount of time a particle spends in a system • Ensures that there is enough dissolved oxygen and no sediment accumulation • Qin So + QfSf = QoutS1 (volume and salinity remain constant) • Exposure time: The amount of time a particle spends in an estuary in total • (a particle can leave with ebb tide a return with rising tide) • Return coefficient, r: ratio between number particles returning to the estuary and the number water particles leaving

  7. SALT WEDGE • Two “wedges” of salt and fresh water • Velocity difference between the two layers creates internal waves at the interface, mixing sea water with fresh water • Example: Mississippi Estuary • Little tidal influence

  8. PARTIALLY MIXED • More influenced by tidal forces create moderately stratified condition • Water column with gradual increase in salinity from surface to bottom • Example: Chesapeake Bay

  9. VERTICALLY HOMOGENEOUS • Tidal flow is greater relative to river discharge • No vertical salinity gradient • Usually created by strong tidal currents at the mouth of an estuary • INTERMITTENT ESTUARY • Varies depending on freshwater input • Changes from solely marine to any other estuary type

  10. ADAPTATIONS IN ESTUARIES • All organisms need to be able to survive drastic changes in salinity (euryhaline) and anoxic condition • _____________________________________________________ • The smooth cordgrass (Spartinaalterniflora) filters salt out of the water • Oysters/ mussels/ clams feed during high tide and stop feeding during low tide • All animals are either osmoregulatorsor osmoconformers • Burrowing to avoid predation and live in stable sediment environment • Bacteria with high oxygen demand burrow in silt to avoid anoxic conditions

  11. OTHER ORGANISMS • Key producers: phytoplankton (diatoms and dinoflagellates) • Turbidity caused by phytoplankton • Fish nurseries for salmon and sea trout • Important for migratory birds • Oyster Reefs • grow on other oysters or other hard surfaces • Macroalgae • Need NO3 and O2

  12. IMPORTANCE OF ESTUARIES • Filter runoff • Absorb floodwaters and dissipate storm surges • Nursery ground for two thirds of US commercial shellfish and fish • Salt marshes and mangrove forests stabilize the shoreline • THREATS TO ESTUARIES • Too many nutrients (eutrophication) • Altered hydrology • Dams can change the salt and fresh water ratio • Toxins from agriculture and industry • Sea level changes

  13. Among some of the most productive ecosystems on Earth – produce more organic material than comparably-sized areas of forest, grassland, agricultural land, etc. • Of 32 largest cities in the world, 22 are located on Estuaries (New York) • Over 100 estuaries in US Random facts

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