Download Brackish Water Ecology

Brackish Water Ecology
Brackish water is formed when
freshwater is mixed with sea
water.
This results in water that is salty
but not as strong as open sea
water.
People rarely think about what
happens when freshwater
environments & marine
environments come together.
Where they meet are called
Estuaries- partly enclosed, coastal
areas that can be formed in one of
four ways.
1) They can be located on
Coastal Plains – a submerged
river valley.
Ex. Chesapeake Bay
2) Fjords – a steep glacier-forged
valley .
Ex. Alaskan Coastline
3) Bar-built Bays/Lagoons – a
parallel offshore sand bar/reef
with partially enclosed
seawater flowing towards the
coast and freshwater runoff
from the coast that dilutes
water behind sand bars.
Coastline of Gulf
of Mexico has
many Bar built
bays
Laguna Madre
4) Tectonic bay –
a shift in
crust at fault
lines that
create lowlying, coastal
areas
Ex. San Francisco
Bay.
Freshwater Source
Saltwater Source
The mixture of freshwater and
sea water results in water
circulation and salinity gradients.
Saltwater is more dense than
freshwater and will always settle
below freshwater when mixed
together forming a halocline.
Diver Floating above Halocline
Divers Surfacing Through Halocline
How water separates in an
estuary:
•Water forms four levels of
salinity concentrations
beginning with 0%o (freshwater)
near the coast line and 35%o
(saltwater) in the open ocean.
Each level has specific
characteristics
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Level 1) Salt wedge – Highly
stratified with Halocline
separating upper layer of lowdensity freshwater from the
bottom layer of high-density
saltwater wedge.
Level 2) Partially Mixed –
Halocline usually poorly
defined.
Level 3) Vertically Heterogeneous
– The Coriolis effect triggers
movement of the saltwater to the
right as it flows into the estuary,
creating mainly freshwater on the
left side of the estuary.
Level 4) Homogeneous – Mixing
is thorough both vertically and
horizontally near to coastline.
Differences in type of water
results in differences in types and
number of species.
Dealing with salinity differences
and maintaining the proper salt
and water balance in cells and in
bodily fluids is one of the
greatest challenges facing estuary
organisms.
Range of travel within an
estuary is determined by how
well organisms tolerate changes
in salinity. Most estuary
organisms are euryhaline species
that tolerate a wide range of
salinities. Some are stenohaline
species and tolerate only a
narrow range of salinities.
Estuary communities are
extremely productive, with
complex food webs; partly
because they are breeding and
nursing grounds for both fresh
and saltwater species.
Bull sharks are
euryhaline species that
actually thrive in the
brackish waters around
estuaries and deltas.
They have been found in
tributaries of the
Mississippi river as far
north as Vicksburg
Bull sharks in the Mississippi