Transitional Transitional Ecosystems -Ecosystems -

Brackish Brackish WaterWater

I. Brackish water –is a term used for areas wherefreshwater combines with salty ocean water.

A. It is not as salty as the oceans B. Examples-bays, inlets, and ocean-flooded river valleys.

C. These partially enclosed ecosystems are

commonly known as Estuaries.

II. Types of Estuaries A. Four different types

B. Classified based on how they were formed.

A. Coastal Plain Estuaries-1. formed by the sea

level rising and filling an existing river valley.2. Chesapeake Bay in Maryland-example

Coastal Plain Estuaries

B. Fjords –

1. U-shaped valleys formed by glacial Action.

2. Developed as sea levels rose slowly over the last 18,000 years, filling river valleys and glacial troughs.

3. Very steep walls are characteristic

4. Northern Europe, Alaska and Canada-examples

Fjords

C. Bar-built Bays/Lagoons – 1. Formed when a shallow lagoon or

bay is protected from the ocean by a sand bar or barrier island.

2. Seawater flowing towards the coast mixes with freshwater runoff diluting water behind the sand bars.

3. The Eastern Seaboard and the Gulf Coast-examples

Bar-built Estuaries

D. Tectonics –1. Formed by the folding or faulting of land surfaces along major fault lines creating low-lying, coastal areas.

2. San Francisco Bay-example

Tectonic Estuaries

III. Halocline

A. Definition – a salinity gradient where two water masses meet. (freshwater and sea water)

B. Denser salt water sinks below the less dense freshwater.

C. Levels of salinity concentration increase from 0 at coastline

to 35ppt (3.5%) in the open sea.

ppt

D. Structure of Halocline

1. Salt wedge – Highly stratified with Halocline separating upper layer of low-density freshwater from the bottom layer of high-density saltwater wedge.

2. Partially Mixed – Halocline usually poorly defined.

IV. Salinity and Species DiversityA. The degree of salt in the water

determines the types of species found in that water.

B. The greatest challenge of estuary

organisms is maintaining water and

salt balance in cells and bodily fluids.

C. Estuary organisms generally tolerate a wide range of salinity.D.Four Classes of Estuary Organisms

1. Freshwater Organisms – species tolerating very little salt.

2. Brackish Water Organisms – species found in mixed salt and freshwater.

3. Euryhaline Organisms – species that tolerate a wide range of salinity.

4. Stenohaline Organisms – species that tolerate only a narrow range of salinity.