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  /estuaries/media/supp_estuar04_coastal.html /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  /estuaries/media/supp_estuar04_barbuilt.html /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  /estuaries/media/supp_estuar04_techtonic.ht ml /estuaries/media/supp_estuar04_techtonic.ht ml

Chesapeake Bay, Canada Flooded River Valley Laguna Madre, Texas Lagoon/Bar-built Glacier Bay, Alaska Fjord San Francisco Bay Tectonic

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 River Salt Wedge Narrangansett Bay Partially Mixed Delaware Bay Vertically Homogenous Spencer Gulf, Aus Inverse

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