Download Chapter 12 - Planet Earth

Chapter 12
Effects of Agriculture on
the Environment
Many environmental problems
result from agriculture:
• Soil erosion
• Sediment transport
and deposition
downstream
• On-site pollution from
fertilizers and
pesticides
• Deforestation
• Desertification
• Degradation of water
aquifers
• Salinization
• Accumulation of toxic
metals and organic
compounds
• Loss of biodiversity
Our Eroding Soils
• U.S. - 1/3 of country’s
topsoil lost
– 1930’s and post WWII
• Loses fertility
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– Increased sunlight
– Warms soil and speeds up
organic decomposition
• Rate of loss of fertility
– Time required for soil to
lose 1/2 of its original store
of the chemical elements
necessary for crops
• Erosion today still greater
than soil regeneration
Where Eroded Soil Goes: Sediments
Also Cause Environmental Problems
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*Sediments choke fisheries
and coral reefs
*Chemical effects: nitrates,
ammonia and other
fertilizers cause lake
eutrophication
* Although erosion has
decreased, still greater
than the rate of soil
regeneration
Where Eroded Soil Goes: Sediments
Also Cause Environmental Problems
Ways to slow erosion:
• Making Soil Sustainable
• Contour Plowing (most effective in recent years)
• No-Till Agriculture
– Combination of farming practices that include
not plowing the land and using herbicides to
keep down weeds.
Controlling Pests
• Insects
• Nematodes
• Bacterial and viral
diseases
• Vertebrates
• Weeds (major problem)
– Compete for resources,
light, water, nutrients and
space
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History of Pesticides
• Removal or use farming methods to decrease
• Chemicals
– Narrow-spectrum pesticide
– Broad-spectrum pesticide
• Petroleum-based sprays and natural plant
chemicals
• Artificial compounds (DDT)
• Biological control
– Predators, parasites and competitors
DDT
• Malaria
• Ideal pesticide
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No short-term effect on people
Seemed to only kill inects
Relatively insoluble in water
Believed transportation not hazardous
• Long-term effects
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Egg production (predatory bird)
Possible increase in cancer in humans
Biomagnification
Storage in fats/oils allows to be transferred biologically
Integrated Pest Management
– Control of agricultural pests (rather than complete
elimination) using several methods together, including
biological and chemical agents
• No or low-till agriculture
• Spatial complexity and biological diversity
• Less damaging
– Goals:
• To minimize the use of artificial chemicals
• To prevent or slow the buildup of resistance by pests to
chemical pesticides
Monitoring Pesticides in the
Environment
• Decompose in place
• Transported
– Wind, surface and subsurface waters
• Sometimes initial product breakdown is toxic
(DDT) or takes a long-time to become non-toxic
– No well established program
– Must monitor concentrations
• Public and environmental health standards
Genetically Modified Crops
• “Novel” changes
– Do not occur in nature; are
more likely to have negative
effects
• Can apply this rule to
three categories of
genetically engineered
crops
– New hybrids
– Terminator gene
– Transfer of genes
New Hybrids
• Occurs naturally
• Increase in agricultural
productivity
• Concerns:
– Superhybrids
– Superweeds
– Marginal lands
The Terminator Gene
• A genetically modified crop which has a
gene to cause the plant to become sterile
after the first year
• In theory, the gene prevents genetically
modified crops from spreading
• Protected “corporately”
• Poor nations
Transfer of Genes
• “Novel” effect
• Can lead to unforeseen
and undesirable
environmental effects
– Potatoes and corn
– Caterpillars
– Monarch butterflies
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Grazing on Rangelands
• Overgrazing occurs when the carrying capacity is
exceeded. It can cause severe damage to lands.
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Trampling stream banks; animal waste
Slows vegetation growth
Reduces plant diversity
Leads to dominance by plant species undesirable to
cattle
– Hastens soil erosion as plant cover decreases
Grazing on Rangelands
• It is important to
properly manage
livestock, including
using appropriate
lands for grazing and
keeping livestock at a
sustainable density
– Density related to
rainfall amounts
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Biogeography of Agricultural
Animals
• Domestic animals introduced into new
habitats
– Native vegetation not adapted to introduced
grazers; may be greatly reduced and threatened
with extinction
– Introduced animals may compete with native
herbivores, reducing their numbers
– Ex: Tropical rainforest to rangeland
Desertification
• Affects 1/6 of the world’s population (largest part
in poorest countries)
• Desertification is the deterioration of land in arid,
semi- arid and dry sub humid areas due to changes
in climate and human activities
• Can be caused by
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Poor farming practices
Conversion of marginal grazing lands to croplands
Poor forestry practices
Soil contamination
Symptoms of Desertification
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Lowering of the water table (deeper wells)
Increase in salt contamination of the soil
Reduced surface water (streams, ponds)
Increased soil erosion (dry soil blown and
washed away)
• Loss of native vegetation (not having
adapted to desert conditions, native
begetation can no longer survive)
Rice in Dry Climates
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• California
• Biggest water users in the
state
• High pesticide and
herbicide use
• Air pollution
• Salmon
• Wetland habitat
• Waterfowl migratory route