Aquatic Ecology
Limnology- study of freshwater
ecosystems
Lentic- standing water
Lotic- moving water
Lentic Ecosystems
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Depressions in land 12,000 meters deep
In northern hemispheres,
glaciers left behind
carved out basins that
filled with rain and snow
Other causes include:
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Silt, driftwood and other
materials that block the
flow of streams
Streams that were flat get
cut off to create “oxbows”
Lentic Ecosystems
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Craters from extinct
volcanoes fill with
water
Lake Formation
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Many lakes are
formed by one of two
mammals
 Humans- dam rivers
for power, irrigation,
digging
 Beavers- dam
streams to form
shallow ponds or
lakes
Lake Layers
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3 layers
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Epilimnion- “upper lake”
consists of a free
circulating upper layer
Metalimnion- also called
thermocline or “middle
lake” has a rapid decline in
temperature (1 degree
Celsius for every meter you
go down)
Hypolimnion- “lower lake”
is the deep, colder layer
Lake Structure
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Littoral zone- shallow
water zone, light reaches
the bottom and it usually
has plants
Emergents- plants
whose roots and stems
are in water but upper
stems and leaves are out
of the water
Limnetic or Pelagic zoneopen water, and has
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Plankton- suspended
organisms
Nekton- free swimming
fish
Lake Zones
Benthic zone- sediment on
bottom of lakes and ponds
•Photic zone- where light
penetrates to the bottom
•Aphotic zone- under
water area where light
does not reach
•Eutrophic- nutrient rich
•Oligotrophic- nutrient poor
•Hypertrophic- excessive
nutrients
Lake Temperatures
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Summer/Spring
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Water is warm on top
and cold on bottom
Lake Temperatures
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Fall/winter
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Temperature on
surface drops and
metalimnion sinks
Epilimnion increases
until all water is the
same temperature\
Water circulates
oxygen and nutrients
Overturn- seasonal
mixing of water
Water Chemistry
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Dissolved Oxygen (DO)
Enters the water through the atmosphere and
photosynthesis
Amount of oxygen the water can hold depends
on pressure, temperature, and salinity
Cold water holds more oxygen that warm water
As atmospheric pressure increases, so does the
amount of oxygen in the water
Oxygen absorbed by the surface is mixed by
turbulence of internal currents
Overturn replenishes oxygen in the water
Water Chemistry
 Carbon
Dioxide
 Carbon dioxide is usually the same
concentration as that in the atmosphere
Water Chemistry
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pH
A measure of the acidic or basic the water is
On a scale of 1-14
1 is very acidic and 14 is very basic
7 is neutral
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Freshwater 3-10
Rainwater 5-6
Streams and lakes 6.5-8.5
Limestone under the water causes the pH to
increase
 (or become more basic)
Lotic Ecosystems
 Flowing
water (rivers and streams)
 Velocity and current decide most things
because it cuts channels and affects living
organisms
 Velocity is determined by size, shape,
gradient of the channel, roughness of
bottom, depth, and precipitation
Streams
 May
begin as outlets of ponds or lakes
 Flow is determined by the lay of the land if
the stream has not been disturbed
 As water flows, it picks up debris that
scrapes the bottom and makes the stream
bigger
Terms
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Meander- bends in streams (aka. Sinuosity)
Watershed- body of land where all runoff
collects in a common body of water
Turbidity- the amount of particles suspended in
water prohibiting light to shine through
Channel- the stream bed and banks formed by
flowing water
Flood Plain- a strip of land that is normally dry
and flat that is on the sides of a river or stream
and is wet during floods.
Terms
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Riparian Zone- the land and vegetation
bordering flowing or standing water
Riffle- a section of a stream where the water is
shallow, fast moving, and is broken into waves
by an obstruction
Siltation- deposition of fine particles (silt) on the
beds of streams or lakes
Pools- water that is relatively deep
Bankfull Width- where water will stop if it comes
out of the stream
How can you tell if a stream is
healthy?
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Stream Quality is determined by
1. Area cover
Do things hang over the stream?
2. Embeddedness
Are there dirt particles on the bottom?
3. Depth
Is the stream shallow or deep?
4. Sediment deposits
Are there sediment build ups?
5. Channel flow
Does water fill up the channel?
Stream quality continued…
6. Channel Alteration
Has concrete, rock, or anything else been added to
the stream?
7. Frequency of riffles or bends
Does the stream curve or have any white water?
8. Bank stability
Are the banks falling into the stream?
9. Vegetative Protection (on the banks)
Are there plants growing on the banks?
10. Riparian zone width
How big is the area on the bank where plants grow?
Stream Chemistry
 pH
• A range of 6-9 is ideal for running freshwater fish
and bottom dwelling invertebrates
• Synergistic Effects
 Happens
when two things combine to
produce effects greater than their sum
 Example.) Pollutants can change the pH
of a stream
Stream Chemistry
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Dissolved Oxygen (DO)
If dissolved oxygen drops
below 5 mg per liter,
aquatic life is stressed
The lower the
concentration, the more
stress
Levels below 1-2 mg per
liter for a few hours result
in “fish kills”
Stream Chemistry
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BOD (biochemical
oxygen demand)
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The amount of oxygen
needed for decomposition
If there is little oxygen,
decomposers that use it
will die
Too much oxygen causes
“gas bubble disease”
Rare
• Oxygen blocks blood
vessels
• Can see bubbles on the
fins and the skin
Stream Orders
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Streams join together to form rivers. Each time
one stream joins another “order” changes.
 A first order stream is one that does not have
any other stream joining it.
 A stream can only increase in order if a stream
of a similar order joins it.
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For example, when a first order stream runs into
another first order stream, it becomes a second order
stream. Likewise, when two second order streams
join each other, it becomes a third order stream and
so on.
Stream Orders
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Order is not increased when a lower order
stream joins one of a larger order.
 Generally:
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First through third order streams are usually called
headwater streams
Fourth through sixth order streams are usually called
medium-sized streams
Above sixth order, the streams become rivers
Lower order streams are usually on steep slopes
compared to higher order streams
 Higher order streams have flood plains
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A
watershed
is a
section of
land where
all the
water
runoff
flows into
a common
basin.
Stream Restoration
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There are many aspects to
stream restoration, but some
suggestions would be:
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Decrease the slope of the
banks (if it will not compromise
or eliminate the riparian zone).
This is generally accomplished
by using a 3:1 ratio.Stream3
ft.1 ft.Bank
• Reduces the stress on
channel walls from flowing
water
• Becomes more stable
• Stops erosion and
sedimentation
• Creates a surface for
vegetation
Stream
3 ft.
Bank
1ft.
Stream Restoration
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Stabilize the Stream Banks
• Riparian Forestation
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Plant native vegetation on the stream banks to stop
erosion. The roots of the plants will hold the soil onto the
banks.
• Add big structures to the banks like wood, stone,
or fabric that will not wash away. Fabric provides a
surface to hold planted vegetation.
• Drive posts into the bank to keep soil from eroding
into the stream.
• Make the channel bigger.
Stream Restoration
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Construct riffles and pools
• Adding large rocks and/or other materials from the
site to the stream prevents natural areas from
being disturbed by trucks hauling rock to the
stream.
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Allows more DO to enter the water
Slows the velocity of flowing water
• Before adding rock to the stream, organic matter
must be cleared from the bottom to be sure the
rock will be stable.
• The rock must be lower than the bank.
Stream Restoration
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Cut and Fill
• Widening the channel in a particular area to allow
water a larger surface to pass over
• If the channel has been cut very deep, the water
will not be able to get into the flood plain. By
adding rock to the bottom of the channel, the water
level is raised allowing it to reach the flood plain if
needed.
Stream Restoration
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Add a waterfall
• Create a difference in elevation allowing the water
to fall. This will increase DO, slow the flow of the
water, and create a habitat for aquatic life.
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Remove garbage