Welcome Envirothonners!. Estuaries What is an estuary? Merriam-Webster defines: a water passage...

Welcome Envirothonners!

EstuariesWhat 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

FundamentalsTide: 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.

Types of estuaries Two ways to classify estuaries

Water CirculationSalt 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

GeologicallyCoastal Plain

East Coast U.S. Sea level rise covered low lying

river valleysDeltas

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

Salt wedge estuaryWhat 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 foundEastern U.S., Mississippi

Water CirculationSalt 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

river valleysDeltas

FjordsWhat are they?

Narrow gorges along sea coast

Why are they?GlaciationHigh river input/low

salt input Low mixing (low D.O.)

Where are they found?Pacific NW

U.S./CanadaScandinavia

Water CirculationSalt wedge (highly

stratified) Mississippi River High river flow/low tidal push Low mixing

river valleysDeltas

Slightly stratifiedWhat 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 deepWhere are they found?

San Francisco Bay, Chesapeake Bay

Vertically mixed Delaware Bay/N. Edisto river,

SC Low river flow/heavy tidal push Well mixed

river valleysDeltas

Vertically mixed

What are they? Estuaries where salinity

is similar at all depthsWhy are they?

Low river input, moderate/strong tidal input

Where are they found?Delaware BayBay of Fundy

East Coast U.S. Sea level rise covered low

lying river valleysDeltas

Coastal Plain EstuariesWhat 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?

river valleysDeltas

DeltasWhat 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 awayRiver carves channels

through delta to its destination

Where are they found?Mississippi River, Nile River

river valleysDeltas

FjordsWhat are they?

Narrow gorges along sea coast

Why are they?GlaciationHigh river input/low

salt input Low mixing (low D.O.)

Where are they found?Pacific NW U.S.Scandinavia

river valleysDeltas

Bar Built EstuariesWhat 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

river valleysDeltas

Techtonic EstuariesWhat 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 areasSan Francisco Bay

Freshwater Estuary

Area where a freshwater river flows into a large body of freshwater such as a lakeFunction 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.

Estuary of Concern

http://www.dfo-mpo.gc.ca/

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 estuariesThink of brackish estuaries (minus the tides, plus

the seiches)

Welcome Envirothonners!. Estuaries What is an estuary? Merriam-Webster defines: a water passage...

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