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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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Presentation on theme: "Announcements – Oct 9, 2006 Review # 2 one week from today. Exam # 2 one week from Wednesday (on October 18th)"— Presentation transcript:

1 Announcements – Oct 9, 2006 Review # 2 one week from today. Exam # 2 one week from Wednesday (on October 18th)

2 Harvesting methods 1) 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

3 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

4 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

5 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)

6 Possible desertification

7 Desertification in China

8 Points to know 1. 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?

9 Human Impacts II Lecture Objectives: 1) Introduce human impacts on freshwater systems 2) Learn about human impacts on marine systems

10 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

11 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, FL 1961 Present

12 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 O 2 & fish kills

13 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.

14 Dams and stream modifications  75,000 dams over 2m tall, plus 2.5 million smaller dams in the U.S. alone

15 Effects of Dams  Benefits: Water supplies Navigation Hydropower Flood Control  Decreased frequency, but increased severity

16 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

17 Biological Effects of Dams  Interrupts fish migration (e.g., salmon) Fish ladders can help Still can have 10-20% fish loss during outmigration

18 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

19 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

20 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


22 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

23 Wetlands: restoration  No-net loss of wetlands rule ~1989 Developers must recreate wetlands they destroy in construction  Are new wetlands really the same?

24 Human Impacts on Marine Systems  Many threats to words oceans  We will focus on: Overfishing Aquaculture Coral reefs

25 Oceanic Fisheries  Worldwide, 25% of animal protein  70% of world’s marine fisheries are overexploited or in danger of becoming overexploited

26 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

27 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


29 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

30 Why overfish?  Technological “Improvements” e.g., Bottom trawlers vs. hook and line  problem of bycatch - killing non-target animals

31 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

32 Overfishing: Bluefin Tuna

33  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

34 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”

35 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)

36 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

37 Audubon Society Seafood Ratings Green – abundant, well managed Farmed mussels and clams Alaska salmon Troll caught Mahimahi U.S. farmed Tilapia Pole/troll caught yellowfin, bigeye, albacore tuna Yellow – some concern over status, manag. Longline caught Mahimahi Pacific cod Rainbow trout Maine lobster Squid (calamari) Canned tuna Red – severe overfishing, poor management Atlantic cod Shrimp Atlantic flounders and soles Sharks Farmed salmon Orange Roughy Chilean seabass (toothfish)

38 Is Aquaculture the answer? AAquaculture - breeding and raising of fish and shellfish for food RRapidly increasing industry PProvides 1/4 world’s marine fisheries

39 Aquaculture AArguments for aquaculture 1. Not depleting natural fish stocks 2. No bycatch 3. More efficient PProblems 1. Still depleting natural fish populations FFeeds often include fishmeal from wild populations 22-5 kg wild fish to produce 1 kg raised fish especially problematic for carnivores fish (e.g. salmon)

40  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


42 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

43 Coral Reefs  One of most diverse and productive ecosystems  Support at least 1/3 marine fish  Protect coasts from storms  Uptake carbon

44 Threats to Coral Reefs  Most threatened marine habitat  Major problems include: 1. Trawling and dynamite fishing - breaks up reefs

45 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

46 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

47 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

48 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?

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