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AQA A-level Environmental Science > Topic 8: Soil Erosion > Flashcards

Topic 8: Soil Erosion Flashcards

1
Q

What is soil erosion?

A

A natural process where soil particles are removed by wind or water

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2
Q

What is the rate of soil erosion like in sois that haven’t been affected by human activity?

A

The same as the rate of soil formation

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3
Q

When is soil erosion an issue?

A

When the rate is faster than that of soil formation

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4
Q

Name the 2 types of soil erosion

A

Wind erosion
Water erosion

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5
Q

When is soil most vulnerable to wind erosion?

A

When it is a dry soil or has a low clay content
This is because they are likely to be loose and there is little cohesion between the particles that would hold the soil together
So the soil blows away

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6
Q

Where is wind erosion a problem?

A

In the area where the soil has been removed
In the area where the soil is deposited- it may cover crops or land in urban areas

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7
Q

Name the types of water erosion

A

Rain splash erosion
Surface runoff erosion
Slumping and landslides

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8
Q

What increases all forms of water erosion?

A

Steeper gradients

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9
Q

Rain splash erosion

A

When soil particles are dislodged by a rain droplet
Soil particles are dispersed in different directions
Those going downhill are more likely to go further

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10
Q

Surface runoff erosion

A

Caused when the infiltration capacity of the soil has been exceeded
Can occur in heavy or prolonged rainfall or if soil is impermeable
Leads water to flow over the ground surface

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11
Q

Slumping and landslides

A

When soil on slopes becomes wet, increased mass and lubrication of water makes it more likely that large amounts of soil will move downwards
Often occurs when deep soil on slopes becomes less stable because of deforestation

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12
Q

Why are landslides more common because of deforestation?

A

The roots of trees that held the soil together decompose
The soil isnt held together as strong
Landslides are more likely after heavy rain

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13
Q

What areas are susceptible to both types of soil erosion?

A

Areas with seasonal rainfall, like Sub-Saharan Africa

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14
Q

Why may areas like sub-Saharan Africa suffer from both types of soil erosion?

A

Wind erosion in the dry season
Rainfall erosion in the wet season

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15
Q

How does vegetation reduce the rate of soil erosion?

A

-it acts as a natural windbreak, reduces wind velocity/kinetic energy that could carry away soil particles
-that and leaf litter reduce the impact of raindrops-soil particles are less likely to be dislodged
-soil organic matter helps to bind soil particles together
-plant roots hold the soil together
-plants held infiltration of water into soil high reduces the rate of runoff, reducing water erosion

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16
Q

What human activities increase the rate of soil erosion?

A

Vegetation removal
Ploughing vulnerable soils
Overgrazing
Reducing soil biota
Soil compaction
Cultivating steep slopes

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17
Q

How can vegetation removal increase soil erosion?

A

Removes protection from erosion

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18
Q

How can ploughing vulnerable soils increase soil erosion?

A

It breaks up soil structure
Soil particle are exposed to erosion as a result of

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19
Q

how can overgrazing increase soil erosion?

A

Vegetation eaten faster than it can grow
Soil is exposed to erosion
Disturbance & root damage by hooves can increase erosion risk

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20
Q

How can reducing soil biota increase soil erosion?

A

Less dead organic matter is broken down

21
Q

How does soil compaction increase soil erosion?

A

Use of heavy machinery
Reduction in soil detrivores
Makes smaller interstitial spaces which reduces the infiltration rate

22
Q

How does cultivating steep slopes increase soil erosion?

A

Surface runoff water flows more rapidly down steeper slopes
More kinetic energy to pick up more soil particles
Ploughing e.g. adds to erosion risk

23
Q

What are the affects of accelerated soil erosion?

A

Reduced productivity
Sedimentation in rivers & reservoirs
Increased atmospheric particulates
Desertification

24
Q

How is productivity reduced because of accelerated soil erosion?

A

Fertile top soil is usually what is eroded
Remaining soil will be less fertile
Plant growth is reduced
Smaller harvests
Shallower soil may also make root penetration difficult

25
Q

How is sedimentation in river and reservoirs an affect of accelerated soil erosion?

A

Soil particles in water may be deposited if they slow down-less kinetic energy
Sediments in rivers reduces flow capacity so river is more likely to overflow and cause flooding after heavy rain

26
Q

How is increased atmospheric particulates an effect of accelerated soil erosion ?

A

Wind erosion increases the amount of atmospheric particulates
Can make health problems like asthma worse

27
Q

Explain desertification as an affect of accelerated soil erosion

A

Soil erosion makes it more difficult for vegetation to grow
Contributing to further soil erosion and reduced rainfall
Leading to the expansion of deserts

28
Q

What are the methods of reducing soil erosion?

A

Long term crops, zero-tillage cultivation, contour ploughing, tied ridging, terracing, rows of stones, windbreaks, multi cropping,increased soil organic matter, livestock management

29
Q

How are long term crops a method of reducing soil erosion?

A

The growth of crops that dont need frequent replanting reduces soil disturbance and erosion rate
E.g. permanent grassland or bush
Tree crops like fruit,tea,coffee,cotton

30
Q

Explain zero-tillage cultivation as a method of reducing soil erosion

A

Cultivation that reduces soil disturbance and therefore erosion
Direct drilling of seeds into the ground- reduces ploughing- reduces disturbance

31
Q

Explain contour ploughing as a method of reducing soil erosion

A

Ploughing on contours at a 90 degree angle to the slope reduces erosion as the water flow is stopped by ploughed furrows and loses its kinetic energy so it cant carry particles
Works until the rainfall is so heavy that the furrow overflows

32
Q

Explain tied ridging as a method of reducing soil erosion

A

Used on almost flat land
Divide a field into crisscross sections for intersecting ridges
They retain water when it rains and increase filtration and reduce runoff

33
Q

Explain terracing as a method of reducing soil erosion?

A

Sloping land is cultivated into a series of narrow fields
Soil is held in place by retaking walls along the contours
Water flowing over the walls is quick but slows down
Most water will infiltrate the soil as a result

34
Q

Explain rows of stones as a method of reducing soil erosion

A

Used if there’s a gentle gradient
Laid along contours to slow runoff and reduce erosion
Any disturbed soil will be deposited

35
Q

Explain how windbreaks can be used as a method of reducing soil erosion

A

Growing crop reduces wind velocity and wind erosion
Field will be exposed when crops re,over
Protection maintained by hedgerows or trees around a field
Hedgerows will reduce the wind velocity for a distance of 30 x its height

36
Q

Explain multi cropping as a method of reducing soil erosion

A

Can redice exposure to wind if they are harvested at different times
Done by human labour rather than machinery

37
Q

Explain increasing soil organic matter as a method of reducing soil erosion

A

Anything that adds organic matter
Will protect soil from wind and rain impact
As it decomposes it will help soil particle adhesion

38
Q

How will livestock management reduce soil erosion?

A

Reduce trampling damage
Reduce livestock near a riverbank where it is more likely to cause erosion into the river
Remove livestock at high-risk times like heavy rain

39
Q

What does the USLE do?

A

Estimate soil loss rates and assess the impact of changes to farming techniques

40
Q

USLE formula

A

A=R x K x L x S x C x P

41
Q

A in the soil loss equation

A

Rate of soil erosion

42
Q

R in the soil loss equation

A

Rainfall erosivity
(The potential ability of soil to be eroded by rain)

43
Q

K in soil loss equation

A

Soil erodability

44
Q

L in soil loss equation

A

Slope length

45
Q

S in the soil loss equation

A

Slope gradient

46
Q

C in the soil loss equation

A

Cropping management
(Impact of vegetation)

47
Q

P in the soil loss equation

A

Erosion control
(Effect of type of ploughing)

48
Q

Under what value will soil loss be considered sustainable ?

A

9 t ha-1 year-1
Which is the natural rate of soil formation

AQA A-level Environmental Science (45 decks)

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