land & soil degradation€¦ · natural soil-forming processes at work insects, decomposition,...
TRANSCRIPT
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The Most
Important Issue
You’ve Never
Heard Of
Land & Soil
Degradation:
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Introduction to Issue
Can be argued that land degradation affects
more people (and other living things) more
seriously than any other environmental
problem
Like many things, most familiar, most mundane
is most important and most easily ignored
After all it’s “just dirt”
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The Gravity of the Problem
“Let us never forget that the cultivation of
the earth is the most important labor of
man. When tillage begins, other arts
follow. The farmers, therefore, are the
founders of civilization.”
Daniel Webster
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Not a New Problem.
Attica (Athens) was no longer
cultivated by true herdsmen,
who made husbandry their
business, and were lovers of
honor, and of a noble nature.
As a result Attica had become
deforested, the soils depleted,
and there are remaining only
the bones of the wasted body –
all the richer and softer parts of
the soil having fallen away. ~
Plato
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Since land degradation (unlike desertification) is defined as resulting fromhuman actions, the global introduction and spread of the problem are closely related to the introduction, spread and growth of human populations and their increasing demands on the natural resource base. However, as has been said many times, numbers alone are not the sole cause: land-use practices, which in turn are influenced by technology amongst a range of other factors, are the primary underlying cause.
Although humanity is thought to have originated in Africa’s rift valley region, the first reasonably well-documented instance of land degradation comes from what used to be called Mesopotamia; the irrigated lands in the Tigris and Euphrates river systems. Here, as in other irrigated drylands of North Africa and later Pakistan, California and elsewhere, the main problems were (and are) secondary salinization, related to waterlogging. Associated with this was a serious decline in soil fertility.
The early initiation and growth of urban civilizations in Mesopotamia in the later part of the 4th millennium BC was related to the development of irrigation. The main crop was wheat. Increasing salinity is reported to have caused a shift from wheat to the more salt-tolerant barley: by around 3500 BC the proportions of the two crops were roughly equal, and by 1700 BC wheat had been abandoned completely. Eventually even barley could not be grown and the populations of the kingdoms of Sumer and Akkad had to abandon the area. Historical evidence from other regions in China, the Indus River Basin, South America and Arizona indicates that similar problems permeate our history. The process forced people to shift to other locations which, in turn, also became salinized in many cases.
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Land Degradation & Poverty
Closely linked to poverty? How?
As the degree of degradation increases,
crop and animal yields decline and people
have both less to eat and less to sell to
support themselves
“If the soil on which agriculture and all human life depend is wasted away, then the battle to free mankind from want cannot be won.” ~ Lord John Boyd Orr, first Director-General of
the UN Food and Agriculture Organization (1948)
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How Big is the Problem? … In 2008, the world's arable land amounted to 1,386
M ha, out of a total 4,883 M ha land used for
agriculture (about ¼ of the earth’s land mass)
United Nations has estimated that about 15% of the
world’s productive farmland has been significantly
affected by some form of land degradation
Arable land percent world
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Four Categories
Erosion
Chemical Deterioration
Physical Deterioration
Desertification
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1 ~ ErosionThe removal of the nutrient-rich layer
of topsoil by either wind or water
Water erosion can occur in any
climate zone
Mostly in places with higher annual rainfall
Wind erosion occurs most commonly
in arid and semi-arid climates Most erosion subtle… over
time
Every spring the 12 Mile Creek
looks brown… that’s evidence of
annual erosion
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Erosion In a mature forest that
is not affected by human activities, the amount of topsoil loss is between 0.004-0.05 tonne per hectare per year.
Relatively minor loss can easily be made up by natural soil-forming processes at work
Insects, decomposition, fungi, etc.
Overall avg. soil erosion for cultivated land in North America and Europe is about 17 tonnes per hectare per year (situation worse in Asia, Africa, South Asia)
300-400 TIMES AS MUCH as in untouched forest
Direct result of change from forest to farmland
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Problems on the SlopesCannot be replaced by soil-forming
processes
Soil erosion becomes even worse when hilly
land is used for farming
Steep slopes obvs. accelerate water
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Terrain Deformation In the case of water erosion Large or small gullies may be cut into
farmers’ fields
Mass movements (landslides) may occur
Case of wind erosion Dunes or deflation hollows –
depressions created when wind removes topsoil from prev. level area
Land may be over-blown – covered by wind-eroded materials from elsewhere
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2 ~ Chemical Deterioration Deterioration of soil as a result of leaching,
salinization, acidification or pollution
A) Leaching To remove soluble or other constituents from by the action of a percolating liquid.
Vital nutrients ( nitrogen, phosphorous, potassium)
can be lost in two ways:
1 – Loss of soil nutrients
Worst in tropical areas where rain washes away soil
and nutrients
Severely leached soils are orange-
red in colour
Dominance of oxides aluminum and iron in soil
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Chemical Deterioration cont…
Leaching is worst in Tropical areas
Worst of all if dense layer of vegetation has been
clear-cut for farming
High yields for few years
Organic material still in soil
Leaching soon strips soil of most essential nutrients
2) Growth of crops
Soil nutrients lost through
farming practices, part. if
same crop grown year after
year
monoculture
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Chemical
Deterioration cont…
B) Salinization
An increase in the
concentration of soluble
salts in the soil to the point
where the soil becomes toxic for plant growth
Greatly accelerated by excessive irrigation
Water used for irrigation carries dissolved salts
that will be left in the soil when the water
evaporates
Salt concentration will eventually reach
dangerous levels (if not properly controlled)
About 1/8 of all irrigated land in the world has
been degraded by severe salinization
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Chemical Deterioration cont…
C ~ Acidification
Land can become acidified by the use of
excessive fertilizers or because of poor drainage
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Chemical Deterioration cont…
D) Emissions
Land can be polluted by emissions from
nearby industries
Or by dumping of liquid or solid wastes
Sludge – treated sewage waste
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3 ~ Physical Deterioration Degradation of land caused by
compaction, waterlogging, or subsidence
Three ways:
Soil can be compacted by the use of heavy machines or by the trampling of herds of animals
Waterlogging obvs., after floods recede from an area, can damage land
Subsidence – sinking of land – can be caused when a significant amount of water is removed from the water table
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4 ~ Desertification Special type of land degradation – refers to the
results of degradation rather than the causes
Occurs when human activities reduce the productivity of an arid or semi-arid area to the point that it resembles a desert
As much as 40% of the world has climates dry enough that they face the possibility of desertification
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The Green Wall…Why is Africa building a Great
Green Wall? BBC News (on
youtube)
https://www.youtube.com/watch?v=4xls7
K_xFBQ&feature=youtu.be
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BREAK! Two hunters are out in the woods when
one of them collapses. He doesn't seem to be breathing and his eyes are glazed. The other guy whips out his phone and calls the emergency services. He gasps, "My friend is dead! What can I do?" The operator says "Calm down. I can help. First, let's make sure he's dead." There is a silence, then a gun shot is heard. Back on the phone, the guy says "OK, now what?"
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We’ve learned of the types of
land degradation…
But what of the causes?
Five Main Categories
Deforestation
Overgrazing
Unsustainable agriculture
Overuse of natural vegetation
Urban/Industrial Pollution
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DeforestationMore than just a few trees cut down…
When large forest areas are cleared for
agricultural use, particularly in tropical
rainforests
“slash and burn” agriculture
Impacts:
Degradation of soil
loss of habitat for millions of species. Seventy
percent of Earth’s land animals and plants live
in forests
Disruption of water cycle and carbon cycle
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Overgrazing herbivory(animal comsumption
of plants) that extracts an
unsustainable yield of floral
biomass from an ecosystem;
More simply, too many grazing
cattle, sheep, or goats can
destroy vegetation beyond its
ability to recover
Soil then exposed to erosion and
leaching
Estimates of overgrazing
worldwide are on the order of
1/3 to ¼ of all rangeland
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Unsustainable Agricultureo Most modern agr., if carried out too intensively so
soil cannot renew itself, reduces nutrient levels and
– in dry areas – may result in salinization as well
o A.k.a. “Agricultural mining”
o Monoculture – large-scale operations growing one
variety of one crop annually
• Healthy ecosystems require complex and
diverse flora and fauna
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Urban/Industrial Pollution Pollution from industrial/commercial factories,
warehouses, mines, etc. can foul the soil
Pesticides, heavy metals, sludge, etc.
E.g., phosphate fertilizer which contains small amounts of cadmium and lead is widely applied
Soil contaminated from agricultural and industrial wastes will produce unhealthy food.
Heavy metals and other toxins enter the food chain & are consumed by human beings.
biomagnification
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Overuse of Natural Vegetation In many developing countries (Near Core and
Periphery), people rely on trees and shrubs for fuel
and for building materials
If pop. dens. of an area becomes too high,
overuse of vegetation can have an impact similar
to that of overgrazing and deforestation
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“A nation that destroys its soils destroys
itself. Forests are the lungs of our land,
purifying the air and giving fresh strength
to our people. ”
Franklin D. Roosevelt