Ecosystem
#3
THE ESTUARY
What is an Estuary?
 A semi-enclosed body of water
where freshwater and saltwater mix
 Other names for estuaries:
Bay
Sound
Lagoon
Inlet
Estuary Classification
 Origin
 Degree of Mixing
Types of Estuaries by Origin
 Coastal Plain
 Tectonic
 Bar Built (or Barrier Island Estuary)
 Fjord
#1: Coastal Plain Estuary
 Most common
 Sometimes
called a Drowned River Valley
 Formed at the end of the last ice age when
rising water flooded (or drowned) existing
river valleys
 Examples:
 Tampa Bay, Chesapeake Bay (MD), Narragansett
Bay (RI)
Coastal Plain Estuary
Chesapeake
Bay (MD)
#2: Tectonic Estuary
 Caused by earthquakes where folding
or faulting may create bays with narrow
inlets to the sea
 Examples:
 San
Francisco Bay
Tectonic Estuary
#3: Bar Built Estuary
 Also called Barrier Island Estuaries
 These are most commonly barrier
islands that are separated from land by
a shallow lagoon
 Usually
shallow with reduced tidal action
 Examples:
 Common
along the Texas and Florida Gulf Coasts
and the Outer Banks of NC
Bar Built Estuary
#4: Fjords
 Valleys that have been cut deeper by
moving glaciers and then invaded by
the sea
 Usually
narrow, straight, long and with
steep sides
 Examples:
 Alaska, Canada, Norway, etc.
Fjords
Estuary Classification
by Stratification
DEGREE OF MIXING
Degree of Mixing?
 Estuaries can be classified by how the
freshwater and saltwater mix
 The basic flow pattern
 Freshwater flows on the surface toward the
ocean while seawater flows into the estuary
below the surface
Most Common Types of Mixing
 Vertically Mixed
 Salinity is consistent from top to bottom
 Slightly Stratified/Partially Mixed
 Lower layers of water typically saltier than upper
layers (Ex. Tampa Bay)
 Highly Stratified/Salt Wedge
 Least
mixed
 Forms when a rapidly flowing large river enters
the ocean in an area where tidal range is low
 Example: Mississippi River
Salt Wedge
Vertically
Mixed
Partially
Mixed
In your notes, draw a sketch of what
each type of mixing would look like!
USE 2 COLORS TO
INDICATE FRESHWATER
VS. SALTWATER AND BE
SURE TO LABEL
Why are Estuaries
Important?
Why are Estuaries Important?
 Habitat for may plants and animals
(including land dwellers like humans &
birds)
 Nursery ground
 Protect water quality by filtering out dirt and
pollution
 Recreation (fish, swim, kayak, bird watch,
etc.)
 Economy (food, fishing charters and other
recreation)
Importance Cont’d…
 Estuaries trap and accumulate sediment and
other nutrients that comes from rivers
 What problems can you foresee with this process…
Eutrophication
 An overabundance of nutrients that causes
an ecological imbalance
 Fertilizer
runoff is also trapped in estuaries
Discussion:
WHAT LIMITS PRODUCTIVITY IN AN
ESTUARY?
IN OTHER WORDS, WHAT MAY KEEP
SOME LIVING THINGS FROM
SPENDING TIME IN AN ESTUARY?
What Limits Productivity in an Estuary?
 Organisms must be able to tolerate a wide
range of salinities
 Osmotic
stress caused by tides
 Decomposition depletes the oxygen in
nutrient rich sediment
 The
rotten egg smell is a result of sulfides
released by anaerobic sulfur bacteria
Everything is Connected!
 How do estuaries contribute to the
productivity of adjacent ecosystems?
 By
increasing the number of individuals that
survive to adulthood
 Safer
 By
than the open ocean
providing nutrients while reducing
eutrophication
Article
Questions
 What is the problem that the article focuses on?
 What was the impact of the problem on the local
community?
 Describe the life cycle of the blue crab. According to the
article, how many are likely to survive to adulthood?
 Why do scientists believe blue crab populations are
down off the coast of GA? What role does the estuary
play in the decrease?
 How could biomagnification play a role in this estuary
food web?
Red Tide
ON THE FRONT LINES OF
RED TIDE DISASTER
AUGUST 2010