Humans in the

BiosphereChapter 6

6-1 A Changing Landscape

Hawaii as an analogy for the EarthLand was limited/finiteNative people were original conservationists: for each palm cut down, replaced with twoProhibited fishing during fish reproductive season

A Changing LandscapeSettlers changed the practices of centuries

Cleared vast areas to grow sugar caneUsed large amounts of fresh water for agriculture

Hawaii todayNative species of animals scarceDrinking water restrictedOnce common fish now rare

Earth as an IslandEarth has a limited resource baseKnowledge of interactions- energy flow, chemical cycling, climate, population-limiting factors- allow us to save ourselves by making predictions

Human ActivitiesHuman activities can change local and global environmentsAmong human activities that affect the biosphere are hunting and gathering, agriculture, industry, and urban development

Hunting & GatheringFirst humans probably caused a mass extinction in North America 12,000 ya – woolly mammoths, zebras, yaks, saber-toothed catsToday, still a few hunter/gatherer groups in world. Most use some form of technology, such as manufactured tools or guns.

AgricultureBy end of last Ice Age (11,000 ya) humans began to farm- wheat, rice, potatoes. Why?

Stable & predictable food supplyLarger settlementsDevelopment of government, laws, writing

Traditional toModern Agriculture

Machinery aided social development – seed drill, plowWorld exploration led to exchange of cropsLarge-scale irrigation in dry areas increased yield

& allowed deserts to become breadbasketsAs specialized techniques developed, farming became a monoculture, with chemical fertilizers and pesticides.

The Green Revolution

In mid-1900s, despite agricultural advances, many food shortages occurred.Result was “miracle strains” of wheat, corn; monoculture; chemical fertilizers.In 20 years, Mexico increase wheat production 10X; India & China produced enough to feed their own peopleWorld food production doubled.

Challenges for the Future

Monoculture leads to problems with pests and diseasesChemical pesticides can damage beneficial insects (pollinators), contaminate water supplies, and accumulate in the environment.Not enough fresh water for irrigation e.g., Midwest & West depends on Ogalla aquifer, which may dry up in 20-40 years at present rate of replenishment

Industrial Growth & Urban Development

For years, cities discarded industrial wastes & pollutants into air, water, & soil without concernUrban sprawl developed consumes farmland & natural habitats, as well as producing stress on environmentCan we learn to control these harmful effects of human activity while preserving- or even improving- our standard of living?

6-2 Renewable & Nonrenewable Resources

“The tragedy of the commons”Free and accessible resources may eventually be destroyed. There is no one responsible for preserving it.Land ResourcesForest ResourcesFishery ResourcesAir ResourcesFreshwater Resources

Classifying ResourcesRenewable resources can regenerate if they are alive, or can be replenished by biochemical cycles if they are nonliving.Nonrenewable resources cannot be replenished by natural processes.Classification depends on context. A single tree is renewable; a population of trees may not be.

Sustainable DevelopmentSustainable development is a way of using natural resources without depleting them.Must take two views into account:

The functioning of ecosystemsThe ways that human economic systems operate.

Land Resources“Land” includes space as well as soil.Soil is a mixture of decayed matter (humus), minerals, sand, clay and silt (from bedrock).

Land ResourcesPlowing removes roots which holds soil in place. This increases the rate of soil erosion by water and wind.Desertification: caused by a combo of farming, overgrazing, and drought.Solutions: contour plowing, leaving previous year’s stems & roots, planting a field with rye rather than naked.

Forest ResourcesWood necessary for many people for homes, paper, fuel in heating & cooking.Living forests often called “lungs of the Earth”- remove CO2 and produce O2.Forests also

Store nutrientsProvide habitatsProvide foodModerate climateLimit soil erosionProtect freshwater supplies

Forest Resources

Is it renewable? Depends on type of forest.Temperate softwood forests of Northeast: renewable. Been logged at least once and have regrown naturally.Alaska and Pacific Northwest are old-growth hardwood forests: never been cut. Takes 100s of years to re-grow, so nonrenewable.

Forest ResourcesDeforestation can lead to

Severe erosion as soil is exposed to heavy rainNutrients in topsoil are washed awayGrazing and plowing that follows can cause permanent changes in soil, making it brick-like and hardSolutions:

Harvest selectively- leaving youngerForesters also maintain tree farmsTree geneticists engineer faster-growing, high-quality wood

Fishery Resources

Example of Chesapeake Bay and river’s watershed: both saltwater & freshwater in estuaries. Has striped bass, American shad, crabs, oysters.Overfishing example: between 1950 and 1990 fish catch grew from 19 million tons to 90 million tons. By the 1990s cod and haddock facing extinction.

Fishery Resources

Sustainable development: Data gathered by ecologists has helped to create guidelines for commercial fishing. Specifies how many and what size fish can be caught. Loss of jobs occurred in short term, but fish populations are recovering.Aquaculture: raising of aquatic animals for human consumption. Can pollute water and damage aquatic ecosystems.

Air ResourcesSmog is caused by pollutants which enter biosphere through land, air or water.Can be caused by burning of fossil fuels which release nitrogen & sulfur compounds, causing acid rain.

Kills plantsChanges chemistry of soilsReleases toxic elements like mercury from soil

Freshwater Resources

Although water is a renewable resource, the total supply of freshwater is limited.

Threat of pollutionImproperly discarded chemicals can enter streams and riversWastes can seep into underground water supplies and wellsDomestic sewage contains N and P which encourage algae & bacteria growthDisease can spread to humans & animals- now most cities treat wastewater

Freshwater Resources¾ of all water consumed in this country is used in agricultureDrip irrigation delivers water directly to plant roots- no runoff!

6-3 BiodiversityBiodiversity = The sum total of the genetically-based variety of all organisms in this biosphere.Ecosystem diversity: includes habitats, communities, and ecological processesSpecies diversity: the number of different species in the biosphere (currently 1.5 million- only millions more to go!)Genetic diversity: The sum total of all the different forms of genetic info carried by all organisms

BiodiversityBiodiversity is one of Earth’s greatest natural resources. Species of many kinds have provided us with

FoodsIndustrial productsMedicines

Painkillers, antibiotics, heart drugs, antidepressants, anticancer drugs

Threats to Biodiversity

Human activity can reduce biodiversity by altering habitats, hunting species to extinction, introducing toxic compounds into food webs, and introducing foreign species to new environments.

Can lead to endangered species and extinction

Habitat AlterationAs habitats disappear, the species that live in those habitats vanish.Development can split ecosystems into pieces, becoming biological islands – habitat fragmentation

Demand for Wildlife Products

Toxic compounds can accumulate in the tissues of organisms. When carnivores eat herbivores which consumed toxic compounds, the substance is concentrated further, called biological magnification.Top level carnivores are at highest risk, though all of food web will be affected.Example: DDT and eagle eggs

Introduced SpeciesIntroduced into new habitats, invasive species that were harmless in their native habitats reproduce rapidly because their new habitat lacks the parasites and predators that control their population “back home”.Example: zebra mussels, purple loosestrife

Conserving BiodiversityConservation: the wise management of natural resources, including the preservation of habitats and wildlifeToday, conservation efforts focus on protecting entire ecosystems as well as single species

Conserving BiodiversityProtecting an ecosystem will ensure that the natural habitats and the interactions of many different species are preserved at the same time.National parks & forestsMarine sanctuariesHunting & fishing regulations

6-4 Charting a Course for the Future

Researchers are gathering data to monitor and evaluate the effects of human activities on important systems in the biosphere.Ozone layer – continually monitoredGlobal climate systems – evaluate change

Ozone Depletion

O3Absorbs UV radiation that can cause cancer, damage eyes, reduce resistance to disease1970s- discovered hole in ozone layer – most likely triggered by CFCs., Since CFC ban hole is getting smaller (very slow deterioration of molecule)

Global Climate Change

Strong evidence shows that the climate patterns are changing from usual cycles.Evidence of global warming due to human activity? Or part of a longterm cycle?Effects of global warming could be flooding of coastal regions, droughts and extreme heat in summer, new organisms thriving and old ones becoming extinct.

The Value of a Healthy Biosphere

Human society depends on healthy, diverse, and productive ecosystems because of the environmental and economic benefits they provide.The biosphere is strong. Humans are clever. We can both adapt.