Estuaries
What is an Estuary? Location where ocean meets a river, either
the ocean enters the river, or at a wide river mouth fresh water enters the ocean where fresh water mingles with salt water
Having turbulence and sediment and nutrient-rich water brings in high levels of nutrients
Classified by… Geomorphology Water Circulation
Geomorphology Geomorphology (geo-earth, morph-form,
ology-study of) is the scientific study of landforms and the processes that shape them
Geomorphological Drowned River Valleys Lagoon/Bar-Built Fjord Tectonic
Drowned River Valleys Drowned river valleys are formed when
river valleys are flooded by rising sea-levels
Most drowned river valleys were formed 15,000 to 6,000 years ago, due to an eustatic rise in sea-level
http://oceanservice.noaa.gov/education/kits/estuaries/media/supp_estuar04_coastal.html
Lagoon/Bar-Built Lagoon/Bar-Built estuaries are partially
separated from the open ocean by barrier beaches (barrier islands/barrier spits)
These barrier beaches intercept the destructive wave forces, therefore protecting the estuary
http://oceanservice.noaa.gov/education/kits/estuaries/media/supp_estuar04_barbuilt.html
Fjord Fjord estuaries are formed in deeply
eroded valleys formed by glaciers They are U-shaped, have steep sides,
and contain sills (shallow barriers) which restrict the flow of salt water into the estuary
Tectonic Tectonic estuaries are formed due to
tectonic activity such as transform faults, and they are filled by a eustatic rise in sea-level
As compared to Lagoon/Bar-Built estuaries that are situated on tectonically stable edges of the continent
http://oceanservice.noaa.gov/education/kits/estuaries/media/supp_estuar04_techtonic.html
Chesapeake Bay, CanadaFlooded River Valley Laguna Madre, Texas
Lagoon/Bar-built
Glacier Bay, AlaskaFjord
San Francisco BayTectonic
Water Circulation Categorized by how the water moves
and mixes within the estuary Mixing of salt and fresh water; what
happens? Water Circulation
Salt Wedge Partially Mixed Vertically Homogenous Inverse Intermittent
Salt Wedge In a salt wedge, river output greatly
exceeds marine input Fresh water floats on top of the
seawater in a layer that thins as it moves seaward. The denser seawater moves landward along the bottom of the estuary, forming a wedge-shaped layer that is thinner as it approaches land
Partially Mixed As tidal forces increases, river output
becomes less than the marine input. Current induced turbulence causes
mixing of the whole water column such that salinity varies, leading to a moderately stratified condition.
Vertically Homogenous Tidal mixing forces exceed river output,
resulting in a well mixed water column The freshwater-seawater boundary is
eliminated due to the intense turbulent mixing and eddy effects
Inverse Inverse estuaries occur in dry climates
where evaporation is greater than the inflow of fresh water
A salinity maximum zone is formed, and both fresh and salt water flow close to the surface. This water is pushed downward and spreads across the bottom, moving both seaward and landward
Intermittent Intermittent estuary type varies
depending on freshwater input, and is capable of changing from a marine bay to any of the other estuary types
Mississippi RiverSalt Wedge
Narrangansett BayPartially Mixed
Delaware BayVertically Homogenous
Spencer Gulf, AusInverse
Mud Flats Created when mud deposits are in
estuaries Often dumped in these estuaries by
tides and rivers
Salinity in Estuaries Salinity in Estuaries generally is the
highest in where the stream or river merges with the ocean, and lowest upstream
Salinity normally rises in the summer and stabilizes in the winter due to evaporation
Salinity also causes the amount of oxygen in the water to decrease as salinity increases
The Anatomy of an Estuary
Famous Estuaries Hudson Bay Estuary Chesapeake Bay Estuary Klamath River Estuary (In Redwood
National Park) San Francisco Bay Estuary
Benefits from Estuaries One of the world’s most productive
ecosystems Provide habitats for fish nurseries Migratory birds used estuaries 60% of the worlds population live by
estuaries or along coasts Provide water filtration and habitat
protection
Salt Marshes A coastal ecosystem in the upper
coastal intertidal zone between land and open salt water or brackish water that is regularly flooded by the tides
Mangrove Various kinds of trees up to medium
height and shrubs that grow in saline coastal habitats, or estuaries
Mangroves dominate three-quarters of tropical coastline
Saline conditions tolerated by various mangrove species range from brackish water, to pure seawater
Mangrove populations have increased