Announcements – Oct 9, 2006

Review # 2 one week from today.

Exam # 2 one week from Wednesday (on October 18th)

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

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

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 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)

Possible desertification

Desertification in China

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?

Human Impacts II

Lecture Objectives:

1) Introduce human impacts on freshwater systems

2) Learn about human impacts on marine systems

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

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

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

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.

Dams and stream modifications

75,000 dams over 2m tall, plus 2.5 million smaller dams in the U.S. alone

Effects of Dams Benefits:

Water supplies Navigation Hydropower Flood Control

Decreased frequency, but increased severity

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

Biological Effects of Dams Interrupts fish migration (e.g., salmon)

Fish ladders can help Still can have 10-20% fish loss during

outmigration

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

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 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

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

Wetlands: restoration No-net loss of wetlands rule ~1989

Developers must recreate wetlands they destroy in construction Are new wetlands really the same?

Human Impacts on Marine Systems

Many threats to words oceans

We will focus on:

Overfishing

Aquaculture

Coral reefs

Oceanic Fisheries Worldwide, 25% of animal protein

70% of world’s marine fisheries are overexploited or in danger of becoming overexploited

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

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

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

Why overfish? Technological

“Improvements” e.g., Bottom trawlers vs.

hook and line problem of bycatch - killing

non-target animals

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

Overfishing: Bluefin Tuna

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

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”

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)

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

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

Is Aquaculture the answer? Aquaculture - breeding and raising of fish

and shellfish for food Rapidly increasing industry Provides 1/4 world’s marine fisheries

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)

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

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

Coral Reefs One of most diverse and productive

ecosystems Support at least 1/3 marine fish Protect coasts from storms Uptake carbon

Threats to Coral Reefs Most threatened marine habitat Major problems include:

1. Trawling and dynamite fishing - breaks up reefs

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

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

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

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?