1) A salt wedge occurs in estuaries where freshwater from rivers meets denser saltwater from the ocean, causing the freshwater to ride up over the saltwater like a wedge. 2) The position of the salt wedge changes with the tides, extending further upstream during flood tides and retreating during ebb tides. 3) Estuaries have muddier bottoms than rivers or oceans due to their slower currents, which allow suspended sediments from rivers to sink to the bottom.

1. 7. Oceanography of an Estuary

2. Salt Wedge-Draw this in your notes:

3. Salt Wedge-Description
• Low density FW overrides high density SW
• Can extend far upstream
• Impacted by tides
– Flood (incoming) – wedge is further upstream
– Ebb (outgoing) – wedge is less far upstream
– Because of it, organisms here must deal with
major salinity fluctuations

4. Substrate (bottom sediments)
• Rivers:
– Current is too fast to let sediment drop out
– Lots of suspended (floating) material
• Estuaries:
– Wider sides, area where water flows opens up (gets
wider) so water is slowed down
– Once flow slows suspended sediments drop out
– Result: estuaries are usually muddy
• Closer to Oceans:
– Currents are stronger
– Smaller particles are washed away leaving larger
sediments behind

5. Read:
http://oceanservice.noaa.gov/educati
on/kits/estuaries/media/supp_estuar0
5a_wedge.html
View:
http://www.youtube.com/watch?v=eeeIgDs4SdY
And
http://www.youtube.com/watch?v=4UyocM9bDL4