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30019- Molecules to Materials: deconstructing the environment > Soil formation and chemistry > Flashcards

Soil formation and chemistry Flashcards

1
Q

Why is soil important? (general areas)

A

Climate
Ecosystem
Pollutants
Water
Health
Plants

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2
Q

Why is soil important for ecosystems?

A

hold 1/4 of the worlds biodiversity

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3
Q

Why is soil important for dealing with pollutants?

A

water filtration system

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4
Q

What can be present in one teaspoon of soil?

A

1 billion organisms
10,000 species
10 kilometres of fungi

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5
Q

Why is soil important for plants?

A

95% food production (CWR)
Building materials
Clothes

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6
Q

Why is soil important for water?

A

400mm can be stored in 1m
1.5 Olympic swimming pools per hectare
60% water return

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7
Q

What is soil composition by volume?

A

45% mineral
5% organic
50% space (air/water)

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8
Q

What is soil composition by mass?

A

0% air
18% water
80% mineral
2% organic

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9
Q

What 5 things is soil formed by?

A

Parent material
Climate
Topography
Time
Biological

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10
Q

How is soil formation affected by parent material?

A

original weathered bedrock transported from elsewhere, usually by wind or water

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11
Q

How is soil formation affected by climate?

A

amount, intensity, timing and type of precipitation that degrades ecosystem into soil

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12
Q

How is soil formation affected by topography?

A

slope and aspect affect the angle of the land and position toward/away from the sun that soil will be exposed to

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13
Q

How can time affect soil formation?

A

the amount of time it takes for four factors to interact with each other

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14
Q

How can biological factors affect soil formation?

A

Plants, animals, microscopic organisms, and humans interact with soil in different ways

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15
Q

What is pedigenesis?

A

process of soil formation

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16
Q

What 2 ways can pedigenesis be?

A

ex-situ
in-situ

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17
Q

What is ex-situ pedigenesis?

A

gravity downslope
Colluvial

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18
Q

What is colluvium?

A

loose, unconsolidated sediments that have been deposited at the base of hillslopes by either rain-wash, sheet-wash, slow continuous downslope creep

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19
Q

What is ex-situ pedigenesis?

A

transported and deposited material

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20
Q

What would earths early soil have been like?

A

simple structure
poor at holding water
lack of nutrients or soil biota

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21
Q

What is the progression to form present day soil?

A

Not much for first few bn yrs
Stramatalites (first algae/ cyanobacteria)
Mosses (465 Ma)
Proper soil development with biota (420-400Ma)
Lichens
Vascular plants (DOM)

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22
Q

What did the development of lichens allow for?

A

rock to be broken down so nutrient cycling

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23
Q

What are some key parent materials?

A

Granite (acidic)
Basalt (basic)
Sandstone
Mudstone and shale (clay material)

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24
Q

What will soil be like in an area with active glaciation?

A

No soil due to scouring of rock by overlying ice

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25
Q

What are the 2 main soil groups?

A

Organic
Mineral

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26
Q

How can you tell the organic layer in soil?

A

Dark black layer in the soil

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27
Q

What are the characteristics of organic soil?

A

Saturated soil or low temp
Low nutrient level
Low pH
High rainfall

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28
Q

Why is organic matter content so high in organic soils?

A

As the conditions aren’t favourable for decomposition and detritivores

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29
Q

What is the organic matter content cut-off for organic soils?

A

> 30%

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30
Q

What is alluvium?

A

loose unconsolidated soil or sediment which has been eroded and reshaped by water and then deposited

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31
Q

What is eluvium?

A

weathered material at or near the source

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32
Q

What are Lacustrine deposits?

A

Clay deposits originally at bottom of lake but the lake in no longer there

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33
Q

What is till?

A

unconsolidated material deposited by glacial ice

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34
Q

What is ablation till?

A

Till that falls onto the top of the glacier from surroundings so doesn’t experience any or little erosional processes

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35
Q

What is basal till?

A

rounded sub-glacial material that is heavily eroded due being dragged along bedrock

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36
Q

What is outwash?

A

Unconsolidated, sorted material deposited by meltwater from a glacier

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37
Q

What is an outwash plain?

A

Accumulation of sediment in front of a end moraine
flat consisting of sand and fine sediments

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38
Q

What will marine deposits be like?

A

Shell, reef and other bits previously at bottom of ocean which has been uplifted

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39
Q

What is eolian deposits?

A

Volcanic ash

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40
Q

What is podzol?

A

A type of soil with string leaching leading to a poor top soil

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41
Q

What are peaty soils important for?

A

Carbon storage

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42
Q

What is leaf litter?

A

Matter which isnt decomposing:
Leaves, needles, twigs, moss etc

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43
Q

What is humus?

A

Rich organic material of plant and animal origin in stage of decomposition

44
Q

What can the O horizon consist of?

A

Several O-layers

45
Q

What is Histosol?

A

Usually more than 30% organic matter
Poor drainage
Cold soil

46
Q

What will the organic matter content of a mineral soil?

A

<30%

47
Q

What will happen to soluble minerals in the soil profile?

A

Readily leached (Ca, Mg, Na)

48
Q

What minerals will tend to accumulate in the soil?

A

Oxides (Fe, Al, Si)

49
Q

What does black colour soil usually mean?

A

Organic matter/ reduced iron
Manganese (purple-black)

50
Q

What does a red soil mean for composition generally?

A

Iron - oxidised (hematite)

51
Q

What does a yellow soil mean for composition generally?

A

Iron - oxidised (geothite)

52
Q

What does a grey-green soil mean for composition generally?

A

Glauconite

53
Q

What does a white soil mean for composition generally?

A

calcium and magnesium carbonates
Gypsum
soluble salts

54
Q

What is a soil profile?

A

vertical cross section of layers of soil in a given area

55
Q

What can the soil profile be sub-divided into?

A

soil horizons

56
Q

What are soil horizons used for?

A

classifying soil types

57
Q

What are soil horizons based on ?

A

colour
texture
roots
structure
rock fragments

58
Q

What is the order for the master soil horizons? (top down)

A

O
A
E
B
C
D/R

59
Q

What is the A horizon?

A

Topsoil/ biomantle of horizons

60
Q

What are the characteristics of the A horizon?

A

Some humus
Darker colour than deeper layers
Usually mixing by biota
Highly productive

61
Q

What is the B horizon?

A

subsoil

62
Q

How might some organic matter reach the B horizon?

A

Leaching

63
Q

What is the E-horizon?

A

Eluviation

64
Q

What will the B horizon be rich in?

A

Clay and minerals (Fe, Al)

65
Q

What are the characteristics of the E horizon?

A

Lighter colour than adjacent horizons
Poor mineral and clay content
Larger soil particles than A or B

66
Q

Why does the E horizon have poor mineral and clay content?

A

leaching (loss water retaining plant nutrients to water table)

67
Q

What is the C horizon?

A

weathered regolith

68
Q

What are the characteristics of the C horizon?

A

Large rocks/ lumps partially broken bedrock
Least affected by weathering
Devoid organic matter

69
Q

What is the D/R horizon?

A

Bedrock horizon

70
Q

What are the characteristics of of the D/R horizon?

A

No rock or boulder just continuous bedrock
Colours those of original rock

71
Q

How many soil classes are there?

A

32

72
Q

What is Andosol?

A

Volcanic soils

73
Q

What is Cambisol?

A

Young soil (brown soil)

74
Q

What is Fluvisol?

A

young alluvial soil

75
Q

What is Gleysol?

A

Water saturated soil

76
Q

What is Histosol?

A

Organic soil

77
Q

What is Leptosol?

A

Shallow poorly developed soil (rocky)

78
Q

What is Regosol?

A

Arid eroding soils
Mountain soils

79
Q

What is Podzol?

A

acidic soils (usually upland coniferous forest)

80
Q

What are the key features that affect soil chemical processes?

A

Texture
pH
Porosity
Water content
Cation exchange capacity

81
Q

What type of system can soil be thought of as?

A

Collodial

82
Q

What is a colloid?

A

mixture of particles ranging between 1 and 1000 nanometres

83
Q

What is the surface area of colloid like?

A

large surface area

84
Q

How active the colloid soil?

A

most chemically active

85
Q

What are the subcategories of soil texture?

A

Sand (<2mm)
Silt (not needed)
Clay (<0.002mm)
Colloid (<0.001mm)

86
Q

How do you usually find colloids?

A

Clay (inorganic)
Degraded organic matter

87
Q

What other name can be given to clay mineral structures?

A

phyllosilicates

88
Q

What does the structure affect in clay minerals?

A

chemical processes- cation exchange (retention and loss of nutrients)

89
Q

What 2 types of sheets can cay minerals be aligned in?

A

Tetrahedral
Octahedral

90
Q

What are 1:1 and 2:1 clays?

A

1:1- 1 layer of tetrahedral to 1 layer of octahedral
2:1- 2 tetrahedra layers to 1 octahedral

91
Q

What does arrangement of the clay layers?

A

reactivity in the soil

92
Q

What is cation exchange capacity?

A

amount of cations a soil can adsorb

93
Q

What is cation exchange capacity the sum of?

A

sum of negative charges on soil particle surfaces

94
Q

What is anion exchange capacity?

A

amount of adsorbed anions

95
Q

What is the structure of tetrahedral sheets?

A

1 silicon
4 oxygen

96
Q

What is an example of a 2:1 clay?

A

Mica

97
Q

What can affect how well cations are attaches to anion in clays?

A

Physical size of cation
Negative charge of clay soil or organic matter
Lower pH
Competition with other cations
Temperature

98
Q

What clay will have the highest cation exchange and why?

A

Vermiculite- sweet spot of gap which allows good negative charge site exposure

99
Q

What is porosity?

A

volume of soil voids that can be filled with
water/air

100
Q

What is bulk density?

A

weight of dry soil per unit volume

101
Q

How can trampling affect measuring carbon stock?

A

actual carbon stock the same but bulk density higher

102
Q

What can pH as a variable be referred to as?

A

the master variable

103
Q

What is the pH range for most soils?

A

5.5-8

104
Q

What are the acid producing processes?

A

Respiration
Mineralisation of organic matter
Leaching
Nitrification
Oxidation of sulfur
Rain (5.6 pH)
Plant uptake of cations

105
Q

Why do we can about soil properties?

A

Nutrient retention - crop growth
Pollution retention
Water holding capacity
Carbon storage

106
Q
A

30019- Molecules to Materials: deconstructing the environment (29 decks)

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