Transcript Human Impact on Aquatic Ecosystems

Human Impact on Aquatic
Ecosystems
1. 40% of the world's oceans are
heavily impacted by human
activities
2. The areas with the least
impact are near the poles
Major Threats to Marine Systems from Human
Activities
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Coastal development – destroys and pollutes coastal
habitats
Runoff from agricultural and urban sources such as
sediment from soil erosion, fertilizer, pesticides,
livestock waste
Pollution from ships and oil spills
Overfishing of commercial fish species
Using fish trawlers (dragging weighted nets across
ocean floor) which degrades and destroys habitat
Introducing invasive species
Human induced climate change
Dissolved Oxygen verses Biochemical
Oxygen Demand
1. Oxygen is measured in its dissolved form as dissolved
oxygen (DO). If more oxygen is consumed than is
produced, dissolved oxygen levels decline and some
sensitive animals may move away, weaken, or die.
2. Biochemical oxygen demand, or BOD, measures the
amount of oxygen consumed by microorganisms in
decomposing organic matter in stream water.
3. BOD directly affects the amount of dissolved oxygen in
rivers and streams. The greater the BOD, the more
rapidly oxygen is depleted in the stream. This means
less oxygen is available to higher forms of aquatic life.
Zone of Hypoxia
Forms from
nutrient overload
of N & P from
fertilizer runoff
(inorganic or
livestock waste) in
streams which
empty into rivers
which empty into
the ocean
Hypoxia Facts
1. 1.7 million tons of nutrients are delivered to the
Gulf of Mexico each year
2. 41% of continental US drains into Gulf of
Mexico
3. 70% of nutrient load comes from agricultural
runoff (surface water runoff form agricultural
land) MOST comes from the MIDWEST
4. 12 million people live in urban area along the
Mississippi River that dump treated sewage
into the Mississippi River
Cause of Hypoxia in the Gulf of
Mexico
Rivers that empty into the Gulf of Mexico that carry runoff from agriculture and
cities contribute to hypoxia in the Gulf of Mexico
Habitat Loss Due to Poor Water Quality:
Threatens Populations
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Algae bloom coats submerged aquatic vegetation (SAV)
which reduces their photosynthetic output.
SAV provides food, shelter, & nursery areas for blue crabs
Blue crabs , but are major predators of benthic
communities and are prey for many other fish species.
Coral Bleaching
1. Corals expel algae from tissues
when stressed; causes corals
to turn completely white
2. Causes of stress include:
–
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Warm water temps
Cold water temps
Lack of light
3. When coral bleaches, it is not
completely dead
4. Corals can survive a bleaching
event, but they are under more
stress & are subject to mortality
Where Coral Bleaching is Occurring
Deepwater Horizon Explosion in Gulf of
Mexico (Possible FRQ this year)
1. 170 million gallons of crude
oil leaked into Gulf of
Mexico
2. The presence of discharged
oil in the environment
causes
 decreased habitat use in
the area
 altered migration
patterns
 altered food availability
 disrupted life cycles
 Oiled plants die,
eliminating the roots that
help bind and stabilize
soil, leading to erosion.
Some of the oil evaporated into the air
as benzene (carcinogen) and hydrogen
sulfide (combines with water to form
acid rain)
How Quickly Oil Traveled
The Clean-up
1. Efforts have focused on
capping, cutting off,
containing, and
capturing oil.
2. These collective efforts
under water and on the
surface of the Gulf were
intended to keep the oil
from reaching coastal
marshes and wetlands
3. Within days there were
reports that oil had
reached coastal areas
and had begun to affect
land and wildlife
4. Oiling continued more
than 100 days after the
explosion: on August 1,
10% of Gulf coast
shoreline miles were
oiled
Freshwater Inland Wetlands:
Vital Sponges
Inland wetlands
act like natural
sponges that
absorb and store
excess water
from storms and
provide a variety
of wildlife
habitats.
Freshwater Inland Wetlands:
Vital Sponges
1. Filter and degrade pollutants
2. Reduce flooding and erosion by absorbing
slowly releasing overflows.
3. Help replenish stream flows during dry periods.
4. Help recharge ground aquifers.
5. Provide economic resources and recreation.
Cultural Eutrophication
1. Phosphate has been the
biggest problem because it
accumulates over time.
2. Nitrate is a lesser problem
because it denitrifies over
time
3. Result can be large fish
kills if not controlled
Correcting Cultural Eutrophication
1. Try to find the source of nutrients (nitrates and phosphates) and stop
them from entering lake
2. Dredge the lake
Dredge: removing sediments and organic
debris from the bottom of the lake and
disposing of them in a different location.
3. Applying ecosystem herbicides to kill invasive / nuisance plants
4. Aerate the lower levels to give oxygen to decomposers
5. Introduce insects that will feed on plants
Introduced / Invasive Species
1. Hydrilla can grow in deep &
shallow water
2. Can grow in water that has 7%
salinity
3. Slows water flow
4. Clogs irrigation and flood-control
canals
5. Crowds out and outcompetes
native species such as
tapeweed, pondweed, and
coontails
1. Zebra Mussels – introduced in
Great lakes from Caspian Sea
2. Filter feeders, eat algae
3. Anchor themselves onto native
mussel species which prevents
native mussels from eating
4. Also clog outlet pipes,
preventing drainage of an area
& can result in flooding
Dams
1. Dams alter the pattern of disturbances that the plants and animals
of a river have evolved
 Many aquatic animals coordinate their reproductive cycles with
annual flood seasons
 Floods provide nutrients for the river’s plants & animals
 Floods provide shallow backwater areas on vegetated land &
shaded riversides which protect young organisms
2. Dams interfere with fish migrations
 Many fish species must move upstream and downstream to
complete their lifecycles.
Largest Hydroelectric Dam in the World
The Three Gorges Dam is the largest hydroelectric dam in the world. It is
located in the middle of the tree gorges on the Yangtze River, (CHINA) the
third longest in the world.
1. How levees affect ecosystems:
a. limit & redirect surface water flow
b. limit the movements of species,
energy, & ecosystem processes
such as fire
2. Levees fail in many ways
• Breach: When a part of the
• levee breaks away, leaving an
• opening for water to flow
• through
• Overtopping: When flood waters
• reach a level higher than the
• levee crest
• Bank erosion
• Slope instability
• Seepage of water through soils
• beneath the levee
Levees
Watersheds
A watershed is area of land where all of the water that is under
it or drains off of it goes into the same place.
1. What word is used to describe the
area around the lowest point of the
river?
Wetlands
2. What are two sources of possible
pollution shown on the map?
sewage treatment plant, runoff
from farm, sediment from
construction
3. Why are wetlands more affected by
pollution than other parts of the
watershed?
They receive pollution from all
water sources that drain into them
Watershed
Divide
1. Label the main river channel on
the map.
2. Look at the spot marked by the
on the map and on the cross
section of the terrain. Notice where
the is pointing. Will pollution
from the site likely affect the
watershed? Why or why not?
Main river
channel