Transcript Human Impacts on Freshwater Ecosystems

Announcements – Oct 9, 2006
Review # 2 one week from today.
Exam # 2 one week from Wednesday
(on October 18th)
Harvesting methods
1) Clear-cutting: economical, but leads to
erosion, loss of plants and animals
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fewer roads needed
reforestation necessary (conifers)
2) Patchwork clear-cutting: smaller,
unconnected clearcuts
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good for deer, rabbits
reduces need for
reforestation
Harvesting methods
3) Selective harvesting: individuals trees
taken
• Less economical
• More roads
• Leaves a more “natural” forest
Debate over “Healthy Forest Initiative”
• Bush policy to decrease risk of forest fires by
allowing selective logging and stream-lining legal
process
• Fire Prone Trees ≠ Desirable Timber Trees
Rangeland ecosystems
Rangelands – lands too dry to support crops, but
receive enough precipitation to support grasses
and drought-resistant shrubs
 wildlife are usually introduced species
Rangeland costs
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Economic & energy – usually low
 common use lands, breed animals, walk
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Environmental – high
 selective grazing can change plant diversity, increase
non-native grasses
 over-grazing
 desertification – process of converting arid and
semi-arid lands to desert (loss of productivity)
Possible desertification
Desertification in China
Points to know
1. Know the 3 main ways humans impact the environment (pollution, movement of
2.
3.
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6.
7.
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9.
exotics & resource use)
What is pollution? What determines how much of it there is?
What are 3 types of material pollution? What are 3 types of energy pollution?
What three types of costs are associated with exploitation of resources? Which ones
are immediate or delayed and why?
What are some problems with loss of biodiversity and extinction? What is a
fundamental challenge in trying to prevent extinction?
Know 4 types of resource exploitation in terrestrial ecosystems
What are some limitations of recycling mineral materials?
Why is tropical deforestation a big problem?
What is desertification? What causes it?
Human Impacts II
Lecture Objectives:
1) Introduce human impacts on freshwater
systems
2) Learn about human impacts on marine
systems
Freshwater Ecosystems
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Invasive Species (e.g., zebra mussel, lamprey) –
already covered
Pollution - will discuss later
Habitat Modification
 Channelization
 Dams
 Draining wetlands
 Changes in terrestrial landscape
Channelization
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Channelization – the
dredging and straightening
of stream channels
Why?
 Divert water for irrigation
 Drain fields for agriculture
 Increase “usable” land
 Prevent flooding
1961
Kissimmee River, FL
Present
Problems with Channelization
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Altered flow regimes
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Many species not adapted
to different flows
Loss of habitat
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Within the stream
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Dredging removes snags,
habitat complexity
Total stream area
Floodplains
low- and no-flow in
remnant channels &
encroaching exotics
led to low O2 & fish
kills
Dams and stream modifications
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Long history of modifying rivers
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Egypt had irrigation ditches by 3200 B.C. and dams
by 2760 B.C.
Dams built per year steadily increased from
around 1800 to a peak in the 1970’s.
Dams and stream modifications
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75,000 dams over 2m tall, plus 2.5
million smaller dams in the U.S. alone
Effects of Dams
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Benefits:
 Water supplies
 Navigation
 Hydropower
 Flood Control
 Decreased
frequency, but
increased
severity
Physical Effects of Dams
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Alterations of flow
 Prevents movement of sediment, nutrients
downstream
 Slower flows upstream
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leads to settling of sediment
reservoirs can fill by as much as 80% in 12 years
More unpredictable flows downstream
Disturbs normal flood-pulse in spring
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Interchange of nutrients between river and floodplains
Biological Effects of Dams
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Interrupts fish migration (e.g., salmon)
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Fish ladders can help
Still can have 10-20% fish loss during
outmigration
Biological Effects of Dams
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Loss of important spawning/foraging habitat in
floodplain
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Net economic loss - river fisheries more productive
than reservoir fisheries
Changes in plant communities, reduced
species richness below dams
Human Health Effects of Dams
Aswan Dam, Egypt –
completed in 1970
Schistosomiasis (Bilharzia )
Parasite passes from
humans to snails to
humans
Irrigation from lake provided
more habitat for snails
Wetlands
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Wetlands – Transitional habitats between aquatic
and terrestrial environments, where water table is
at or near the surface
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Includes marshes, swamps, bogs, estuaries,
temporary ponds, etc.
Estimated loss of 53% of total wetlands in U.S.
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9.2 million acres lost between 1950’s-1970’s
2.6 million acres lost between 1970’2-1980’s
current loss of 124,000 acres per year
Wetland Loss
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Wetlands provide important ecosystem services
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1. Mitigate flooding
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2. Retention of sediments, nutrients, pollutants
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Natural sewage treatment plants
3. Wildlife habitat
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20% of threatened and endangered species associated with
wetlands
Important habitat for waterfowl
Wetlands: restoration
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No-net loss of wetlands rule ~1989
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Developers must recreate wetlands they destroy in
construction
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Are new wetlands really the same?
Human Impacts on Marine Systems
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Many threats to words oceans
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We will focus on:
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Overfishing
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Aquaculture
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Coral reefs
Oceanic Fisheries
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Worldwide, 25% of animal protein
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70% of world’s marine fisheries are overexploited
or in danger of becoming overexploited
Oceanic Fisheries
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Number of fish caught rose steadily until 1990’s,
but per capita number caught decreased
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Human population growing faster than increase in catch
Leads to increased demand and overfishing
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many species commercially extinct - no longer
economically profitable to harvest
Sustainable harvest
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Ideal strategy: harvest population to maximize
growth rate
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determines how quickly fish can be removed, while
still maintaining healthy stock
too little or too much harvest, population grows
slowly
keep population at half carrying capacity
Most
fisheries harvest too much
Why overfish?
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Economics - Tragedy of the Commons
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Each group tries to maximize individual returns at
expense of common resource
Quota problems
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Often a fixed number, not percentage
Harvesting constant number of decreasing
population leads to severe impacts
Why overfish?
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Technological
“Improvements”
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e.g., Bottom trawlers vs.
hook and line
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problem of bycatch - killing
non-target animals
Overfishing Example: Bluefin Tuna
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Large, wide ranging, fast animal
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Grows to 1500 lbs.
Swims up to 50 mph
Can migrate across oceans
One of most valuable and overexploited fish
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Single fish sold for $172,000 in Tokyo
fish market auction - sashimi
Adult population declined 90% since
1975
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250,000 to about 22,000
Overfishing: Bluefin Tuna
Overfishing: Bluefin Tuna
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International Commission for the Conservation
of Atlantic Tunas (ICCAT) responsible for
management
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Manages tunas and tuna-like species (marlins,
swordfish)
Supposed to manage for maximum sustainable
yield
Has scientific committee
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Compile catch statistics and models population
trends
Overfishing: Bluefin Tuna
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Commission’s managers repeatedly ignored
scientists’ advice
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e.g., 1981 own scientific committee concluded
Atlantic tuna population depleted, quotas should
be set close to zero
Set 1160 metric ton quota for “scientific study”
Overfishing: Bluefin Tuna
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Population continued to decline, but doubled
quota
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Early 1990s - Sweden wanted to list bluefin on
CITES (Convention on International Trade in
Endangered Species)
Overfishing: Bluefin Tuna (cont.)
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Lobbying by U.S., Canada, and Japan,
forced Sweden to accept compromise
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50% reduction in catch
Population still extremely low
Why did efforts fail?
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1. Lack of commitment by Commission
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conflicts of interest - some work for seafood
industry
2. Quota problem - number not percent
3. Lack of international support
4. Non-member nations
Audubon Society Seafood Ratings
Green –
Yellow – some
Red – severe
abundant, well concern over
overfishing, poor
managed
status, manag. management
Farmed mussels
and clams
Alaska salmon
Troll caught
Mahimahi
U.S. farmed Tilapia
Pole/troll caught
yellowfin,
bigeye, albacore
tuna
Longline caught
Mahimahi
Pacific cod
Rainbow trout
Maine lobster
Squid (calamari)
Canned tuna
Atlantic cod
Shrimp
Atlantic flounders and
soles
Sharks
Farmed salmon
Orange Roughy
Chilean seabass
(toothfish)
http://www.audubon.org/campaign/lo/seafood/seafood_wallet.pdf
Is Aquaculture the answer?
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Aquaculture - breeding and raising of fish
and shellfish for food
Rapidly increasing industry
Provides 1/4 world’s marine fisheries
Aquaculture
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Arguments for aquaculture
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1. Not depleting natural fish stocks
2. No bycatch
3. More efficient
Problems
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1. Still depleting natural fish populations
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Feeds often include fishmeal from wild populations
2-5 kg wild fish to produce 1 kg raised fish
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especially problematic for carnivores fish (e.g. salmon)
Aquaculture
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Problems (cont.)
 2. Fish wastes
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3. Genetic diversity
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aquatic pollution, disease spread
raised fish escape and breed with wild fish
reduces genetic diversity
can cause migration problems
4. Can still be bycatch
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if wild fish used to stock pens/ponds
Milkfish in Philippines
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85% of fry collected NOT milkfish
Aquaculture
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Problems (cont.)
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5. Habitat destruction - loss of mangroves, coastal
wetlands habitats
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provide nursery habitat for fish/shellfish
protect coast from storms
help control floods
trap sediments
filter and clean water of excess nutrients
Solutions?
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Reduce fishmeal in feeds, raise more herbivorous fish
(e.g. Tilapia), regulations on building new facilities
Coral Reefs
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One of most diverse and productive
ecosystems
Support at least 1/3 marine fish
Protect coasts from storms
Uptake carbon
Threats to Coral Reefs
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Most threatened marine habitat
Major problems include:
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1. Trawling and dynamite fishing - breaks up
reefs
Threats to Coral Reefs
2. “Bleaching” - death/loss of algae
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Triggered by stress
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elevated temperatures
pollutants
Frequency and severity have increased in the
last decade
Threats to Coral Reefs
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Problems (cont.)
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3. Runoff
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4. Aquarium industry
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sediments, pollutants
collect best coral, animals
5. Global warming
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rising sea levels - corals need shallow water
rising temperatures
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corals exist in very narrow temperature range
Solutions - creating marine reserves, control
development, regulate collecting
Why should I care about coral reefs?
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Tourism
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Countries w/reefs get about 50% of their GNP from
reef activities
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Beach protection from waves
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Medical uses
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AZT, 50% of cancer research, bone-grafting
Biodiversity
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1% of ocean floor houses 25% of marine species
Points to know
1) What is channelization? Why is it done and what problems can it
2)
3)
4)
5)
6)
cause?
What can be the problems with dams and flood control? How do
they affect sediment & water flows, fish migration, and floodplains?
What is a wetland and how much has been lost in the U.S.? What
ecosystem services do they provide?
Why is oceanic fishing important (2 reasons)? Name 3 reasons for
overfishing. What does the bluefin tuna example tell us about the
effects politics & conflict of interests on fishing policies?
What are the pros and cons of aquaculture?
Why should you care about the destruction of coral reefs?