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• 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

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

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

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 + Qf Sf = Qout S1 (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

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

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

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

ADAPTATIONS IN ESTUARIES

• All organisms need to be able to survive drastic changes in salinity (euryhaline) and anoxic condition

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• The smooth cordgrass (Spartina alterniflora) filters salt out of the water

• Oysters/ mussels/ clams feed during high tide and stop feeding during low tide

• All animals are either osmoregulators or osmoconformers

• Burrowing to avoid predation and live in stable sediment environment

• Bacteria with high oxygen demand burrow in silt to avoid anoxic conditions

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

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

• 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