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