Chapter 6: Humans in the Biosphere

6.1 A Changing Landscape

The Effect of Human Activity

• @@People affect the environment through agriculture, development, and industrial growth@@
  • These activities affect the quality of Earth’s natural resources, including soil, water, and the atmosphere
• Farmers have been able to double the world’s food production over the last 50 years through monoculture - a farming strategy of planting a single, highly productive crop year after year
  • However, monoculture can pollute soil and water; in addition to this, running farm machinery and producing fertilizer both use a lot of fossil fuels
• Societal development into dense human communities has produced much waste that can pollute the land, air, and water resources
  • Moreover, spreading development uses up farmland and divides natural habitats into fragments
• Though the Industrial Revolution of the 1800s has led to many modern conveniences, it takes a lot of energy to produce and power these modern conveniences
  • Burning fossil fuels and dumping waste into the environment can harm the environment

Sustainable Development

• @@Sustainable development uses natural resources to meet human needs without causing long-term damage to the environment@@
• There are two main types of natural resources
  • A renewable resource is a resource that can be produced or replaced by healthy ecosystem functions
  • Ex: a single southern white pine tree that can grow in place of an old tree that dies or is cut down
  • A nonrenewable resource is a resource that cannot be replenished by natural processes within a reasonable amount of time
  • Ex: fossil fuels that take millions are years to form

6.2 Using Resources Wisely

Soil Resources

• Many things we need depend on healthy soil, including crops for food production and paper from trees
• The mineral- and nutrient-rich portion of the soil is called topsoil
  • Topsoil can be renewable if it is managed well, but good topsoil is produced by many years of interactions between soil and plants
  • Unfortunately, topsoil can be damaged or lost quickly
• Soil erosion happens when wind or water take soil away; it is often worse if land is plowed and left bare between plantings
  • Sometimes, farming, overgrazing, and very little rain can turn farmland into desert, a process called desertification
• The loss of forests, called deforestation, can also harm soils and lead to severe soil erosion
  • Over half of the world’s old-growth forests (forests that have never been cut) have already been lost to deforestation
  • Soils and microclimates can change so much that trees cannot grow there again
• Farming practices such as crop rotation and leaving stems and roots in the soil between plantings can help protect soil from erosion and a loss of nutrients, and cutting only some mature trees and using tree farms can also protect soil

Freshwater Resources

• Although fresh water is usually considered a renewable resource, some sources of fresh water are not renewable
• Only 3 percent of the water on Earth is freshwater; therefore, we must be careful to protect the ecosystems that collect and purify fresh water
• Freshwater sources can be affected by different kinds of pollution
  • A pollutant is any harmful material that can enter land, water, or air
  • When a pollutant enters water supplies from one spot, the source is called a point source (such as a factory or an oil spill)
  • When pollutants enter from many smaller sources, the sources are called nonpoint sources (such as grease and oil washed off of roads or chemicals released into the air by factories and cars)
  • Sometimes, a pollutant remains in the ecosystem for a long time
  • For example, DDT is a cheap, long-lasting type of pesticide that controls agricultural pests and mosquitoes; but when DDT gets into rivers and lakes, it can have serious effects
    • These effects are caused by a process called biological magnification - the increasing concentration of a harmful substance in organisms at higher trophic levels in a food chain or food web
  • A few ways to make sure we have enough water are to protect ecosystems involved in the water cycle, cut pollution rates, and waste less water

Atmospheric Resources

• The atmosphere has a direct effect on health, giving us the oxygen we need to breathe
• The upper atmosphere contains a form of oxygen called ozone that protects us from the sun’s ultraviolet radiation
• The atmosphere also contains other gases such as carbon dioxide, methane, and water vapor, called greenhouse gases, that help keep the Earth’s temperature stable
  • Natural concentrations of these greenhouse gases in the atmosphere control Earth’s temperature, but by raising greenhouse gas concentrations, human activity plays a role in causing global warming and climate change
• There are many forms of air pollution, including smog, acid rain, greenhouse gases, and particulates
  • Smog is a gray-brown haze in the air formed by chemical reactions among air pollutants that form ozone
  • Near ground level, ozone is dangerous, especially to people with difficulty breathing
  • Burning fossil fuels releases chemicals that combine with water vapor in the air to form acids; when the acids fall as rain, it is called acid rain
  • In some areas, acid rain damages leaves and changes the chemistry of soil and surface water; it can also release toxic elements from soil, allowing them to move through the biosphere
  • Particulates are tiny pieces of ash and dust released by some industrial processes and by some diesel engines
  • Very small particulates can cause serious health problems when they enter the lungs
  • Efforts are improving the air quality around the world, including the banning of lead gasoline

6.3 Biodiversity

The Value of Biodiversity

• Biodiversity is the total of all the genetically based variation in all organisms in the biosphere
• There are three levels of biodiversity: ecosystem diversity, species diversity, and genetic diversity
  • Ecosystem diversity means the many different kinds of ecosystems that exist in the biosphere
  • Species diversity is the number of different species in the biosphere or in a particular place
  • Genetic diversity can mean all the different forms of genetic information carried by one species or by all organisms on Earth
• Many medicines are based on substances in wild species, including aspirin and penicillin
  • When we lose biodiversity, we lose genetic information that may have been useful in medicine
• Genetic diversity is also important in agriculture. Most crop plants have wild relatives that may carry genes for such important features as disease resistance and pest resistance
  • If we lose the wild plants, we may lose those genes
• The number and variety of species in an ecosystem can affect the ecosystem’s health
  • Sometimes changes in the population of a single species can change the whole ecosystem
  • Healthy and diverse ecosystems are also important for soil, water, and air quality

Threats to Biodiversity

• People reduce biodiversity by changing habitats, hunting, and introducing species into new places; pollution and climate change also lower biodiversity
• Often, people change a natural habitat into farmland or land for housing
  • Development often breaks a habitat into smaller pieces, a process known as habitat fragmentation that forces organisms to compete for resources
• People can push species to extinction by hunting them
  • Habitat fragmentation is very hard on hunted animals, as it leaves the hunted animals with fewer hiding places
• The introduction of an invasive species is also a threat to biodiversity, as the new species may out-compete native plants and animals
• Pollution and climate change also threaten biodiversity

Conserving Biodiversity

• To preserve biodiversity, we need to protect individual species as well as whole ecosystems, as well as keep human interests and needs in mind
• The Association of Zoos and Aquariums (AZA) tries to protect organisms, one species at a time; by choosing and managing mating pairs in their captive breeding program, they are trying to increase genetic diversity
• The United States has national parks, forests, and other protected areas focused on protecting entire ecosystems rather than individual species
• In order to protect biodiversity, people, and industries, need to change their habits

6.4 Meeting Ecological Challenges

Ecological Footprints

• The ecological footprint describes our impact on the biosphere and is the total amount of functioning ecosystem needed both to provide the resources a human population uses and to absorb the wastes that population generates
  • An ecological footprint can be used to determine the carrying capacity for humans
• Ecologists talk about the ecological footprint of individuals, of countries, and of the world’s population, though it is difficult, if not impossible, to calculate an exact footprint
  • To calculate the ecological footprint of an entire country, researchers first calculate the footprint of an average citizen; then they multiply that footprint by the population of the country
  • The average American has an ecological footprint of more than four times the global average
• @@Ecologists follow three basic steps that can lead us to a sustainable future: (1) recognize the problem; (2) find the cause; (3) change behavior@@