Understanding Estuaries: Nature's Diverse Waterways Explained

1. Welcome Envirothonners!

2. Estuaries • What is an estuary? • Merriam-Webster defines: a water passage where the tide meets a river current or an arm of the sea at the lower end of the river

3. Fundamentals • Tide: Rise and fall of sea levels as a result of the moon’s gravity, the sun’s gravity, and the rotation of the earth all of which effect the dynamics of the tide (Height/Flow Rate) • Water density: Cold water is denser than warm water, and saltwater is denser than freshwater • Seiches (sayshes): atmospheric or seismic conditions that may cause a landlocked body of water (freshwater) to resemble tidal effects.

5. Types of estuaries Two ways to classify estuaries • Water Circulation • Salt wedge (highly stratified) • Mississippi River • High river flow/low tidal push • Low mixing • Fjords • Norway, Alaska, B.C. • Freshwater rides on top of salt • Low mixing • Slightly stratified • Chesapeake Bay • Some moderate mixing • Saltier deeper • Vertically mixed • Delaware Bay/N. Edisto river, SC • Low river flow/heavy tidal push • Well mixed • Geologically • Coastal Plain • East Coast U.S. • Sea level rise covered low lying river valleys • Deltas • Mississippi River, Nile river • Deposits of silt/mud • Fjords • Norway, Alaska, B.C. • Large, glacial cut valleys • Bar built • Outer banks of NC • Formed by sand deposits/barrier islands • Lagoons • Tectonic • San Francisco Bay • Caused by faulty faults

6. Salt wedge estuary • What is it? • Estuary where freshwater floats on top and salt penetrates up river in the deeper part of the water column • highly stratified • Why is it? • Where fast flowing rivers meet low – moderate tidal influence • Saltwater denser than freshwater • Where are they found • Eastern U.S., Mississippi River

7. Types of estuaries Two ways to classify estuaries • Water Circulation • Salt wedge (highly stratified) • Mississippi River • High river flow/low tidal push • Low mixing • Fjords • Norway, Alaska, B.C. • Freshwater rides on top of salt • Low mixing • Slightly stratified • Chesapeake Bay • Some moderate mixing • Saltier deeper • Vertically mixed • Delaware Bay/N. Edisto river, SC • Low river flow/heavy tidal push • Well mixed • Geologically • Coastal Plain • East Coast U.S. • Sea level rise covered low lying river valleys • Deltas • Mississippi River, Nile river • Deposits of silt/mud • Fjords • Norway, Alaska, B.C. • Large, glacial cut valleys • Bar built • Outer banks of NC • Formed by sand deposits/barrier islands • Lagoons • Tectonic • San Francisco Bay • Caused by faulty faults

8. Fjords • What are they? • Narrow gorges along sea coast • Why are they? • Glaciation • High river input/low salt input • Low mixing (low D.O.) • Where are they found? • Pacific NW U.S./Canada • Scandinavia

9. Types of estuaries Two ways to classify estuaries • Water Circulation • Salt wedge (highly stratified) • Mississippi River • High river flow/low tidal push • Low mixing • Fjords • Norway, Alaska, B.C. • Freshwater rides on top of salt • Low mixing • Slightly stratified • Chesapeake Bay • Some moderate mixing • Saltier deeper • Vertically mixed • Delaware Bay/N. Edisto river, SC • Low river flow/heavy tidal push • Well mixed • Geologically • Coastal Plain • East Coast U.S. • Sea level rise covered low lying river valleys • Deltas • Mississippi River, Nile river • Deposits of silt/mud • Fjords • Norway, Alaska, B.C. • Large, glacial cut valleys • Bar built • Outer banks of NC • Formed by sand deposits/barrier islands • Lagoons • Tectonic • San Francisco Bay • Caused by faulty faults

10. Slightly stratified • What are they? • Estuaries where River input is less than Marine input • Salinity is higher deeper (why?) • Why are they? • The mixing results from turbulence more than other things (i.e. tide or river flow) • Generally very deep • Where are they found? • San Francisco Bay, Chesapeake Bay

11. Types of estuaries Two ways to classify estuaries • Water Circulation • Salt wedge (highly stratified) • Mississippi River • High river flow/low tidal push • Low mixing • Fjords • Norway, Alaska, B.C. • Freshwater rides on top of salt • Low mixing • Slightly stratified • Chesapeake Bay • Some moderate mixing • Saltier deeper • Vertically mixed • Delaware Bay/N. Edisto river, SC • Low river flow/heavy tidal push • Well mixed • Geologically • Coastal Plain • East Coast U.S. • Sea level rise covered low lying river valleys • Deltas • Mississippi River, Nile river • Deposits of silt/mud • Fjords • Norway, Alaska, B.C. • Large, glacial cut valleys • Bar built • Outer banks of NC • Formed by sand deposits/barrier islands • Lagoons • Tectonic • San Francisco Bay • Caused by faulty faults

12. Vertically mixed • What are they? • Estuarieswhere salinity is similar at all depths • Why are they? • Low river input, moderate/strong tidal input • Where are they found? • Delaware Bay • Bay of Fundy

13. Types of estuaries Two ways to classify estuaries • Water Circulation • Salt wedge (highly stratified) • Mississippi River • High river flow/low tidal push • Low mixing • Fjords • Norway, Alaska, B.C. • Freshwater rides on top of salt • Low mixing • Slightly stratified • Chesapeake Bay • Some moderate mixing • Saltier deeper • Vertically mixed • Delaware Bay/N. Edisto river, SC • Low river flow/heavy tidal push • Well mixed • Geologically • Coastal Plain • East Coast U.S. • Sea level rise covered low lying river valleys • Deltas • Mississippi River, Nile river • Deposits of silt/mud • Fjords • Norway, Alaska, B.C. • Large, glacial cut valleys • Bar built • Outer banks of NC • Formed by sand deposits/barrier islands • Lagoons • Tectonic • San Francisco Bay • Caused by faulty faults

14. Coastal Plain Estuaries • What are they? • Areas where Sea level rise since end of the last Ice Age (10,000-18,000 years ago) have flooded low lying river valleys • Why are they? • Low lying river valleys were easily covered with water (low points) • Where are they found? • Eastern U.S. (Chesapeake Bay) • Bay of Fundy?

15. Types of estuaries Two ways to classify estuaries • Water Circulation • Salt wedge (highly stratified) • Mississippi River • High river flow/low tidal push • Low mixing • Fjords • Norway, Alaska, B.C. • Freshwater rides on top of salt • Low mixing • Slightly stratified • Chesapeake Bay • Some moderate mixing • Saltier deeper • Vertically mixed • Delaware Bay/N. Edisto river, SC • Low river flow/heavy tidal push • Well mixed • Geologically • Coastal Plain • East Coast U.S. • Sea level rise covered low lying river valleys • Deltas • Mississippi River, Nile river • Deposits of silt/mud • Fjords • Norway, Alaska, B.C. • Large, glacial cut valleys • Bar built • Outer banks of NC • Formed by sand deposits/barrier islands • Lagoons • Tectonic • San Francisco Bay • Caused by faulty faults

16. Deltas • What are they? • Estuaries that form at the mouth of LARGE rivers. Resemble the shape of Δ. • Why are they? • Silt deposits build up rather than wash away • River carves channels through delta to its destination • Where are they found? • Mississippi River, Nile River

17. Types of estuaries Two ways to classify estuaries • Water Circulation • Salt wedge (highly stratified) • Mississippi River • High river flow/low tidal push • Low mixing • Fjords • Norway, Alaska, B.C. • Freshwater rides on top of salt • Low mixing • Slightly stratified • Chesapeake Bay • Some moderate mixing • Saltier deeper • Vertically mixed • Delaware Bay/N. Edisto river, SC • Low river flow/heavy tidal push • Well mixed • Geologically • Coastal Plain • East Coast U.S. • Sea level rise covered low lying river valleys • Deltas • Mississippi River, Nile river • Deposits of silt/mud • Fjords • Norway, Alaska, B.C. • Large, glacial cut valleys • Bar built • Outer banks of NC • Formed by sand deposits/barrier islands • Lagoons • Tectonic • San Francisco Bay • Caused by faulty faults

18. Fjords • What are they? • Narrow gorges along sea coast • Why are they? • Glaciation • High river input/low salt input • Low mixing (low D.O.) • Where are they found? • Pacific NW U.S. • Scandinavia

19. Types of estuaries Two ways to classify estuaries • Water Circulation • Salt wedge (highly stratified) • Mississippi River • High river flow/low tidal push • Low mixing • Fjords • Norway, Alaska, B.C. • Freshwater rides on top of salt • Low mixing • Slightly stratified • Chesapeake Bay • Some moderate mixing • Saltier deeper • Vertically mixed • Delaware Bay/N. Edisto river, SC • Low river flow/heavy tidal push • Well mixed • Geologically • Coastal Plain • East Coast U.S. • Sea level rise covered low lying river valleys • Deltas • Mississippi River, Nile river • Deposits of silt/mud • Fjords • Norway, Alaska, B.C. • Large, glacial cut valleys • Bar built • Outer banks of NC • Formed by sand deposits/barrier islands • Lagoons • Tectonic • San Francisco Bay • Caused by faulty faults

20. Bar Built Estuaries • What are they? • Estuaries that are lagoon-like areas often found behind barrier islands or large sand bars. • Why are they? • Occur where wave deposition has built up sand bars or barrier islands • Where are they found? • Folly Beach, SC? • Cape Hatteras OBX, NC

21. Types of estuaries Two ways to classify estuaries • Water Circulation • Salt wedge (highly stratified) • Mississippi River • High river flow/low tidal push • Low mixing • Fjords • Norway, Alaska, B.C. • Freshwater rides on top of salt • Low mixing • Slightly stratified • Chesapeake Bay • Some moderate mixing • Saltier deeper • Vertically mixed • Delaware Bay/N. Edisto river, SC • Low river flow/heavy tidal push • Well mixed • Geologically • Coastal Plain • East Coast U.S. • Sea level rise covered low lying river valleys • Deltas • Mississippi River, Nile river • Deposits of silt/mud • Fjords • Norway, Alaska, B.C. • Large, glacial cut valleys • Bar built • Outer banks of NC • Formed by sand deposits/barrier islands • Lagoons • Tectonic • San Francisco Bay • Caused by faulty faults

22. Techtonic Estuaries • What are they? • Estuaries found near fault lines that result from tectonic activity • Why are they? • Tectonic forces cause areas to drop below sea level, allowing seawater to rush in and fill it • Tectonic forces also cause freshwater drainages to empty into them • Where are they found? • Coastal mountainous areas • San Francisco Bay

23. Freshwater Estuary • Area where a freshwater river flows into a large body of freshwater such as a lake • Function similar to brackish water estuary • Little to no tidal influence • Chemically different waters of the rivers (input) and the lakes (sink) can mix in similar ways as the brackish water estuaries • Temperature differences can also imfluence mixing (why?) • Most mixing between the systems is caused by seiches. • May have a tidal effect but without regularity. • Where are they? • Large bodies of freshwater… • Hint: Lake Cumberland is NOT big enough.

24. Estuary of Concern http://www.dfo-mpo.gc.ca/

25. Remember… • Tides, river flows, and geology define estuaries • There are two ways to classify estuaries • Mixing and geologically • Mixing is result of tides, river flow and geological shape of estuary • Geology generally results from glaciation, physical action (i.e. erosion, waves, storms, plate techtonics etc), even anthropogenic causes (dredging, beach renourishment, etc) • There are also freshwater estuaries • Think of brackish estuaries (minus the tides, plus the seiches)