Estuaries

1. Estuaries

2. Form where river meets the sea • Regions of constant environmental change • Importance to marine ecosystems • Organic material enriches ocean waters • Protection from predators (ex: juvenile fish) • Support many commercially important animals that humans rely on for food • Fish nurseries • Fragile habitats • Pollution • Damage by dams Block freshwater supply

3. Embayment: coastal area partially cut off from the rest of the sea Freshwater mixes with saltwater to form an estuary Physical Characteristics of Estuaries

4. Types of Estuaries • Coastal plain (drowned river valley) • Form between glacial periods • Form when rising water levels from melting glaciers flood coastal plains and low-lying rivers

5. Types of Estuaries • Tectonic • Earthquakes caused land to sink, allowing seawater to cover it

6. Types of Estuaries • Fjord • Form when glaciers carve large valleys in coastal areas • Filled with water after glaciers retreated

7. Types of Estuaries • Bar-built • Form when geographic barriers form a wall between freshwater and saltwater

8. Salinity and Mixing Patterns • Salinity varies vertically and horizontally • Least salty near the mouth of the river • Freshwater flows over the seawater • Surface water is less dense and flows out to sea • Denser saltwater from ocean moves into estuary along the bottom • Called positive estuary • Negative estuary  lose more water through evaporation than the river is able to replace • Low in productivity (nutrient poor)

9. Salt-wedge estuary • In mouths of rivers flowing into saltwater • Well-mixed estuary • River flow is low and tidal currents play major role in water circulation

10. Partially mixed estuary • Have strong surface flow of freshwater and strong influx of seawater • Temperature • Changes rapidly with air temperature changes • Estuaries are heated by the sun

11. Estuarine Productivity • High because of freshwater and saltwater mixing • Silt and clay deposits absorb any excess nutrients from surrounding water • Release back into water when nutrients are in short supply • Filter feeders remove more phytoplankton • Excess phytoplankton eliminated as pseudofeces • Large, semisolid particles

12. Life in an Estuary • Fewer species • Less competition for food and space • Feed on a variety of foods

13. Maintaining osmotic balance • Have body fluids with same concentration of salts as seawater • Isosmotic to surrounding water • Have tissues and cells that tolerate dilution (osmoconformers) or maintain optimal salt concentration in their tissues (osmoregulators)

14. Estuarine Communities • Many are euryhaline species • Can tolerate a broad salinity range • Oyster reefs  oysters growing on the shells of previous generations • Mud flats  contain rich deposits of organic material with small inorganic sediment grains

15. Seagrass meadows  extract nutrients from sediments • Salt marsh community • Temperate and subarctic regions • Low and high marsh regions • Mangrove communities • Tropical regions • Little wave action • Sediments accumulate that lack oxygen