1. Brackish Water Ecology

2. Brackish water is formed when freshwater is mixed with sea water
Brackish water is formed when freshwater is mixed with sea water. This results in water that is salty but not as strong as open sea water.

3. People rarely think about what happens when freshwater environments & marine environments come together. Where they meet are called Estuaries- partly enclosed, coastal areas that can be formed in one of four ways.

4. 1) They can be located on Coastal Plains – a submerged river valley.
Ex. Chesapeake Bay

5. 2) Fjords – a steep glacier-forged valley .
Ex. Alaskan Coastline

6. 3) Bar-built Bays/Lagoons – a parallel offshore sand bar/reef with partially enclosed seawater flowing towards the coast and freshwater runoff from the coast that dilutes water behind sand bars.

7. Coastline of Gulf of Mexico has many Bar built bays

8. Laguna Madre

9. 4) Tectonic bay – a shift in crust at fault lines that create low-lying, coastal areas Ex. San Francisco Bay.

10. Freshwater Source
Saltwater Source

11. The mixture of freshwater and sea water results in water circulation and salinity gradients. Saltwater is more dense than freshwater and will always settle below freshwater when mixed together forming a halocline.

12. Diver Floating above Halocline

13. Divers Surfacing Through Halocline

14. How water separates in an estuary:
Water forms four levels of salinity concentrations beginning with 0%o (freshwater) near the coast line and 35%o (saltwater) in the open ocean. Each level has specific characteristics

16. Level 1) Salt wedge – Highly stratified with Halocline separating upper layer of low-density freshwater from the bottom layer of high-density saltwater wedge. Level 2) Partially Mixed – Halocline usually poorly defined.

17. Level 3) Vertically Heterogeneous – The Coriolis effect triggers movement of the saltwater to the right as it flows into the estuary, creating mainly freshwater on the left side of the estuary. Level 4) Homogeneous – Mixing is thorough both vertically and horizontally near to coastline.

18. Differences in type of water results in differences in types and number of species. Dealing with salinity differences and maintaining the proper salt and water balance in cells and in bodily fluids is one of the greatest challenges facing estuary organisms.

20. Range of travel within an estuary is determined by how well organisms tolerate changes in salinity. Most estuary organisms are euryhaline species that tolerate a wide range of salinities. Some are stenohaline species and tolerate only a narrow range of salinities.

21. Estuary communities are extremely productive, with complex food webs; partly because they are breeding and nursing grounds for both fresh and saltwater species.

22. Bull sharks are euryhaline species that actually thrive in the brackish waters around estuaries and deltas. They have been found in tributaries of the Mississippi river as far north as Vicksburg

23. Bull sharks in the Mississippi