announcements – oct 9, 2006 review # 2 one week from today. exam # 2 one week from wednesday (on...
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Announcements – Oct 9, 2006
Review # 2 one week from today.
Exam # 2 one week from Wednesday (on October 18th)
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Harvesting methods1) Clear-cutting: economical, but leads to
erosion, loss of plants and animals• fewer roads needed• reforestation necessary (conifers)
2) Patchwork clear-cutting: smaller, unconnected clearcuts
• good for deer, rabbits• reduces need for
reforestation
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Harvesting methods3) 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
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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
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Rangeland costs Economic & energy – usually low
common use lands, breed animals, walk
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)
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Possible desertification
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Desertification in China
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Points to know1. Know the 3 main ways humans impact the environment (pollution, movement of
exotics & resource use)
2. What is pollution? What determines how much of it there is?
3. What are 3 types of material pollution? What are 3 types of energy pollution?
4. What three types of costs are associated with exploitation of resources? Which ones are immediate or delayed and why?
5. What are some problems with loss of biodiversity and extinction? What is a fundamental challenge in trying to prevent extinction?
6. Know 4 types of resource exploitation in terrestrial ecosystems
7. What are some limitations of recycling mineral materials?
8. Why is tropical deforestation a big problem?
9. What is desertification? What causes it?
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Human Impacts II
Lecture Objectives:
1) Introduce human impacts on freshwater systems
2) Learn about human impacts on marine systems
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Freshwater Ecosystems Invasive Species (e.g., zebra mussel, lamprey) –
already covered Pollution - will discuss later Habitat Modification
Channelization Dams Draining wetlands Changes in terrestrial landscape
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Channelization
Channelization – the dredging and straightening of stream channels
Why? Divert water for irrigation Drain fields for agriculture Increase “usable” land Prevent flooding
Kissimmee River, FL1961
Present
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Problems with Channelization
Altered flow regimes Many species not adapted
to different flows Loss of habitat
Within the stream Dredging removes snags,
habitat complexity Total stream area Floodplains
low- and no-flow in remnant channels & encroaching exotics led to low O2 & fish kills
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Dams and stream modifications
Long history of modifying rivers 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.
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Dams and stream modifications
75,000 dams over 2m tall, plus 2.5 million smaller dams in the U.S. alone
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Effects of Dams Benefits:
Water supplies Navigation Hydropower Flood Control
Decreased frequency, but increased severity
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Physical Effects of Dams Alterations of flow
Prevents movement of sediment, nutrients downstream
Slower flows upstream 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
Interchange of nutrients between river and floodplains
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Biological Effects of Dams Interrupts fish migration (e.g., salmon)
Fish ladders can help Still can have 10-20% fish loss during
outmigration
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Biological Effects of Dams Loss of important spawning/foraging habitat in
floodplain Net economic loss - river fisheries more productive
than reservoir fisheries
Changes in plant communities, reduced species richness below dams
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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
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Wetlands Wetlands – Transitional habitats between aquatic
and terrestrial environments, where water table is at or near the surface Includes marshes, swamps, bogs, estuaries,
temporary ponds, etc.
Estimated loss of 53% of total wetlands in U.S. 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
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Wetland Loss Wetlands provide important ecosystem services
1. Mitigate flooding
2. Retention of sediments, nutrients, pollutants Natural sewage treatment plants
3. Wildlife habitat 20% of threatened and endangered species associated with
wetlands Important habitat for waterfowl
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Wetlands: restoration No-net loss of wetlands rule ~1989
Developers must recreate wetlands they destroy in construction Are new wetlands really the same?
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Human Impacts on Marine Systems
Many threats to words oceans
We will focus on:
Overfishing
Aquaculture
Coral reefs
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Oceanic Fisheries Worldwide, 25% of animal protein
70% of world’s marine fisheries are overexploited or in danger of becoming overexploited
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Oceanic Fisheries Number of fish caught rose steadily until 1990’s,
but per capita number caught decreased Human population growing faster than increase in catch
Leads to increased demand and overfishing many species commercially extinct - no longer
economically profitable to harvest
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Sustainable harvest Ideal strategy: harvest population to maximize
growth rate 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
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Why overfish? Economics - Tragedy of the Commons
Each group tries to maximize individual returns at expense of common resource
Quota problems Often a fixed number, not percentage Harvesting constant number of decreasing
population leads to severe impacts
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Why overfish? Technological
“Improvements” e.g., Bottom trawlers vs.
hook and line problem of bycatch - killing
non-target animals
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Overfishing Example: Bluefin Tuna Large, wide ranging, fast animal
Grows to 1500 lbs. Swims up to 50 mph Can migrate across oceans
One of most valuable and over-exploited fish Single fish sold for $172,000 in Tokyo fish market
auction - sashimi Adult population declined 90% since 1975
250,000 to about 22,000
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Overfishing: Bluefin Tuna
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Overfishing: Bluefin Tuna International Commission for the Conservation
of Atlantic Tunas (ICCAT) responsible for management Manages tunas and tuna-like species (marlins,
swordfish) Supposed to manage for maximum sustainable
yield Has scientific committee
Compile catch statistics and models population trends
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Overfishing: Bluefin Tuna Commission’s managers repeatedly ignored
scientists’ advice 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”
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Overfishing: Bluefin Tuna
Population continued to decline, but doubled quota
Early 1990s - Sweden wanted to list bluefin on CITES (Convention on International Trade in Endangered Species)
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Overfishing: Bluefin Tuna (cont.) Lobbying by U.S., Canada, and Japan,
forced Sweden to accept compromise 50% reduction in catch
Population still extremely low Why did efforts fail?
1. Lack of commitment by Commission conflicts of interest - some work for seafood
industry 2. Quota problem - number not percent 3. Lack of international support 4. Non-member nations
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Audubon Society Seafood Ratings
Green – abundant, well managedFarmed mussels
and clamsAlaska salmonTroll caught
MahimahiU.S. farmed TilapiaPole/troll caught
yellowfin, bigeye, albacore tuna
Yellow – some concern over status, manag.Longline caught
MahimahiPacific codRainbow troutMaine lobsterSquid (calamari)Canned tuna
Red – severe overfishing, poor managementAtlantic codShrimpAtlantic flounders and
solesSharksFarmed salmonOrange RoughyChilean seabass
(toothfish)
http://www.audubon.org/campaign/lo/seafood/seafood_wallet.pdf
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Is Aquaculture the answer? Aquaculture - breeding and raising of fish
and shellfish for food Rapidly increasing industry Provides 1/4 world’s marine fisheries
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Aquaculture Arguments for aquaculture
1. Not depleting natural fish stocks 2. No bycatch 3. More efficient
Problems 1. Still depleting natural fish populations
Feeds often include fishmeal from wild populations 2-5 kg wild fish to produce 1 kg raised fish
especially problematic for carnivores fish (e.g. salmon)
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Aquaculture Problems (cont.)
2. Fish wastes aquatic pollution, disease spread
3. Genetic diversity raised fish escape and breed with wild fish reduces genetic diversity can cause migration problems
4. Can still be bycatch if wild fish used to stock pens/ponds Milkfish in Philippines
85% of fry collected NOT milkfish
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Aquaculture Problems (cont.)
5. Habitat destruction - loss of mangroves, coastal wetlands habitats provide nursery habitat for fish/shellfish protect coast from storms help control floods trap sediments filter and clean water of excess nutrients
Solutions? Reduce fishmeal in feeds, raise more herbivorous fish
(e.g. Tilapia), regulations on building new facilities
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Coral Reefs One of most diverse and productive
ecosystems Support at least 1/3 marine fish Protect coasts from storms Uptake carbon
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Threats to Coral Reefs Most threatened marine habitat Major problems include:
1. Trawling and dynamite fishing - breaks up reefs
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Threats to Coral Reefs
2. “Bleaching” - death/loss of algae Triggered by stress
elevated temperatures pollutants
Frequency and severity have increased in the last decade
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Threats to Coral Reefs Problems (cont.)
3. Runoff sediments, pollutants
4. Aquarium industry collect best coral, animals
5. Global warming rising sea levels - corals need shallow water rising temperatures
corals exist in very narrow temperature range
Solutions - creating marine reserves, control development, regulate collecting
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Why should I care about coral reefs?
Tourism Countries w/reefs get about 50% of their GNP from
reef activities
Beach protection from waves
Medical uses AZT, 50% of cancer research, bone-grafting
Biodiversity 1% of ocean floor houses 25% of marine species
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Points to know
1) What is channelization? Why is it done and what problems can it cause?
2) What can be the problems with dams and flood control? How do they affect sediment & water flows, fish migration, and floodplains?
3) What is a wetland and how much has been lost in the U.S.? What ecosystem services do they provide?
4) 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?
5) What are the pros and cons of aquaculture?
6) Why should you care about the destruction of coral reefs?