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Chapter 12
Human Impacts upon Earth
• Historical Basis of Pollution
• Pollution: Human released products in the
amounts and durations that cause adverse effects.
• Two primary factors that affect damage done
– technological “inventions”
– population size
• Biodegradable
– Easily broken down into simpler compounds
• Non-biodegradable
– Won’t break down or break down very slowly
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• Population size: wastes produced faster than
ecosystem could dispose.
– Sewage
• Urban centers enhanced this problem.
• Eliminate “misery and disease”: often causes
other problems.
• Pesticides.
• Often, pollution is in the eye of the beholder.
– Uranium ore
– arsenic in water
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Renewable and Nonrenewable Resources
• Natural Resources: things usable by humans, but
which cannot be “created” by humans.
• limited and unlimited
• intensive exploitation moves unlimited to limited
resources.
• renewable
• vs.
• nonrenewable
“natural
processes”
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Mineral Resources—non-renewable
• Locations of mineral resources is not based on
political boundaries
• international trade required to bring in all types
needed
• (U.S. & Canada has about 5.2% of world’s
population, and consumes about 30% of mineral
resources.)
• Costs
– Economic Costs ($$ to exploit resource)
– Energy Costs (to do the exploiting)
– Environmental Costs (pollution, habitat loss etc)
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Steps : each step has costs
• Exploration
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time & technology
some energy
some environmental
becomes more intense as “easy” resources are
consumed.
• Mining
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Labor
Equipment
Energy (large costs)
Environmental (significant)
• mine tailings
• water pollution & erosion
• land disturbance
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Refining (often part of mining)
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labor
equipment
energy
environmental
• air pollution
• water pollution
Transportation
– energy
– some environmental
Manufacturing
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labor
equipment
energy
environmental
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Recycling
• Can save significant costs by using materials
which do not require all of the above steps.
• As energy costs go up, recycling will become
more common.
• Many pay the environmental costs, rather than the
few who use a product.
• H/W must be able to collect easily and must have
high economic value
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Pristine Areas
• Remote areas with harsh conditions are typically
pristine (e.g. arctic poles, mountain tops, open
ocean)
– Areas that won’t support agriculture.
– Won’t support dense human population
• Other areas which until recently have been
unaffected are being impacted.
– will support limited agriculture or other human uses.
• As human population grows.....
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• Many “parks” and protected areas have been
designated as pristine areas become more rare.
• “Wilderness” areas: where humans are visitors,
and do not remain. (U.S. definition)
• Parks becoming more noticeable in Africa, C/S/N
America, Australia
– Until recently had large amount of relatively untouched
land, now trying to preserve it
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Modifications by Humans
About 40% of world’s land surface converted to
cropland and permanent pasture.
Forest
• Originally, 1/2 of U.S., 3/4 of Canada, 9/10 of
Europe, and much of rest of world.
• Very large demand for wood.
• Sustained yield: harvest rate equals rate of
regrowth.
• Tropical forests are currently treated as
nonrenewable resource, with extremely fast rate of
depletion
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Forests reduce energy in rainfall, and
practically stop erosion by slowing runoff.
– Water is “evapo-transpirated” in large volumes.
– Shade and humidity moderate temperature
extremes.
Tropical forests trap much CO2 but are in areas
of highest population growth pressures.
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Management of forests require a compromise
between economic forces and environmental
viewpoints.
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Clear-cutting
Patchwork clear-cutting
Selective harvesting
Reforestation
• Different species need different things in a
forest (e.g. Red-Cockaded Woodpecker)
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• Deciding what to do with a forest requires a
conscious decision:
– known value of world’s forests
– can assign value to wildlife and water within
– Wilderness value is very difficult to determine
.... and forest can not be both an economic
resource and a wilderness area.
• Have to choose in some cases or find way to satisfy
both sides of issue
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Rangelands
• Arid and semiarid lands that can’t support typical
agriculture, but can support some grazing animals.
• Grazing animals selectively reduce some plant species
(and inadvertently encourage others). Managers do the
same.
• Most grazing animals which are herded are “exotic”
species, and reduce native species.
• Population pressures force people to graze too many
animals (Tragedy of the Commons), remove trees for
wood (nutrient removal) and push land towards
“desertification”.
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Aquatic Systems
• Large areas of the ocean are still considered
pristine.
• Most productive areas in the oceans are close to
shore:
– nutrients/sunlight/ offshore currents bring nutrients up
from bottom
– Concentrates pressure
• Fishing selectively removes some species.
• Methods for catching bottom dwellers disturbs
habitat and wastes 25% of fish caught
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• Most freshwater systems have been altered by
humans.
– water quality changes
– exotic species
– thermal pollution
• Many systems are manipulated to enhance some
desirable species.
– Recreational and commercial interests
• Difficult to predict all the consequences of
managing large natural systems.
• Difficult to manage all inputs to lake that may
affect ecosystem
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Wildlife Management
• Improving conditions for species desirable to
humans. Manipulate one of the following:
• -food and water
• -cover (shelter):
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-escape from competitors
-protection from weather
-resting and sleeping
-mating and raising young
• Quail
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• Must understand niche very well before
attempting “habitat management”.
• Trying to improve the habitat for one
species often harms the habitat of another.
– Difficult role to try and take over mgmt of
• Migrating species require special
considerations.
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Natural Selection and Extinction
• Extinction: elimination of all individuals of a
particular species (local and global).
• Natural phenomenon .... estimated that only about
1 or 2% of all species which have existed are still
alive today.
• Speciation: appearance of a new species.
• Since things change, a species must adapt or
become extinct.
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Extinction happens more often when:
• species has small population/low
reproduction rate
• dispersed individuals
• species occurs in small, restricted areas
• species is very specialized
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Accelerated Extinction
• Humans are among the most successful species
currently on earth:
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adaptable
Intelligent
high reproductive capability
few enemies
As human population grows:
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other species displaced (habitat alteration)
species utilized as food
used as ornaments
used for medicine
eliminated as pests
=accelerated extinction
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Why worry?
• Many species may be useful to us.
– food & medicine
• Certain species play key roles in the ecosystems
that we utilize.
• Most people find nature beautiful, and
“monocultures” are found disturbingly sterile.
• Do all species have a fundamental right to exist?
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Actions:
• Protection of “threatened” and “endangered”
species.
• More action in developed nations than in less
developed nations.
• Bias in protecting certain types of species:
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birds
mammals
butterflies
a few mollusks, fish and plants
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World Conservation Union (former International Union
for the Conservation of Nature)
Work (without much power, but much prestige) around
the world, especially in less developed nations.
U.S. Endangered Species Act (1973)
• Attempts to protect threatened and endangered
species from governmental actions.
• Political amendments and effects
– Endangered Species Review Committee
• Can sanction extinction if economic benefits warrant
– Weakened ability to add species to list