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Biogeochem - Ernest > Biogeochem - Leaching > Flashcards

Biogeochem - Leaching Flashcards

1
Q

What is an ion?

A

a charged element or compound

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2
Q

What are the factors/processes that lead to soil nutrient concentration

A

1) geoavailability of a nutrient (dependent on the parent rock composition)

2) Chemical and physical weathering

3) the soil solution nutrient concentration

4) bioavailability of the nutrients

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3
Q

controls of geoavailability

A

abundance
access of weathering agents and degree of wethering (climate, porosity, topographic relief)
mineral properties
geochemical conditions

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4
Q

controls of dispersivity (physical processes)

A

abundance and geoavailability
grain characteristics (eg size, shape)
climate
topography
movement through the air
movement through the water

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5
Q

controls of mobility (chemical processes)

A

abundance and geoavailability
solubility of primary and secondary minerals
speciation
mineral properties
pH and redox conditions
photolysis
tendency for volatilisation
tendency for biotransformation

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6
Q

what is soil leaching?

A

the loss of ions or soluble materials from soil pore water due to water movement

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7
Q

what is the ‘formation of secondary minerals’

A

the precipitation of an ion that was dissolved in a solution with oxygen is added

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8
Q

What climatic soils (ie temperate, tundra, tropical etc) features the most leaching?

A

Tropical rainforest soils

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9
Q

how does temperature and climate impact the rate of soil leaching

A

Higher temperatures promote chemical and biological reactions which can use up the ion in the soil

higher rainfall rates cause greater levels of soil percolation, meaning more water is available to dissolve solutes and transport it through the soil profile

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10
Q

what do clay soils tend to be water logged

A

because the particles are small, this means the pore spaces is also small resulting in the water moving / draining slower through the soil

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11
Q

What sort of elements would you expect to find in highly weathered soils?

A

Aluminium oxide
Iron oxides (Fe(III))
Silicon dioxide
Potassium

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12
Q

What is the cation exchange capacity (CEC)?

A

the capacity of a certain amount of soil to bind ions

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13
Q

What does a higher Cation Exchange Capacity (CEC) value mean?

A

the soil has a higher capacity to retain cations

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14
Q

What is adsorption

A

a substance adheres to the surface of a soil or liquid

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15
Q

what is desorption

A

the release of substances from a soil particle surface back into the water or air

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16
Q

Are nutrients bioavailable in solution or attached to soil particles?

A

in solution

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17
Q

How does a low pH (acidic) promote soil leaching

A

Acidic soils have more H+ ions which are taken up by teh soil particles, releasing cations like Ca, Mg, K, Na into solution which can be flushed away

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18
Q

do organic matter rich soils have a high or low CEC value

A

high

mean it can hold more nutrients and can make them available over time

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19
Q

What pH is reached when an acidic soil is at equilibrium

A

3

20
Q

what does a pH equilibrium of 3 result in in acidic soils?

A

the production of abundant Aluminium rich soils

21
Q

What is produced when you weather pyrite?

A

sulphuric acid

22
Q

what product is formed in alkaline soils?

A

carbonates form

23
Q

What is the alkaline pH equilibrium and what does it form an equilibrium with?

A

8.3

they form an equilibrium with the CO2 in the soil atmosphere

24
Q

What is the pH range of most soils in the uk?

A

pH 3.3-8.5

25
Q

What is the pH for most agricultural soils

A

6 to 7

26
Q

how do high levels of rainfall impact soil fertility?

A

abundant levels of rainfall introduces more carbonic acid into the soil, increasing the rate of leaching and resulting in the soil being less fertile

27
Q

what is the process in which calcium is leached out of the soil due to high rainfall causing soils to become more acidic?

A

Higher rainfall causes more carbonic acid to be introduced to the soil. This results in cation exchange capacity (CEC) occurring where calcium is desorped and hydrogen ions from the carbonic acid (H2CO3) are adsorbed. This leaves the calcium in solution which is then leached out of the soil as calcium bicarbonate (Ca(HCO3)2) due to the higher volumes of water

28
Q

are water logged soils oxic or anoxic?

A

anoxic

29
Q

are soils oxic or anoxic below the water table?

A

anoxic

30
Q

what does water-logging cause?

A

the gleying of soils

31
Q

properties of gley soils

A
  • very clayey
  • influenced by high groundwater levels
  • unusual colours (greyish)
  • unusual smells due to fermentation and sulphate reduction
32
Q

when and how does gleying occur?

A

when the water table rising resulting in anoxic conditions

Anoxic conditions causes other elements to be used as electron acceptors (eg sulphate, nitrate, iron oxides (2 and 3), manganese oxides (3 and 4). This changes the properties of the soil

This can cause to conditions to become less acidic as the microbial activities consume some of the hydrogen ions increasing the pH.

occurs in arid areas

33
Q

what might happen to particles at low pH?

A

they may disintegrate

34
Q

Does leaching occur during a positive or negative water balance?

A

positive water balance

35
Q

what is a positive water balance?

A

where precipitation is much greater than evapotranspiration

36
Q

what is the capillary fringe

A

the zone immediately above the water table into which water is drawn upwards due to capillary action

37
Q

what are pedalfers?

A

Soils with a high p/e value (above 48)

38
Q

what characterises pedalfers?

A

high levels of rainfall (causing high p/e value) which causes leaching

39
Q

what are/is podsols/podsolisation?

A

Podsolisation is the process in which podsol soils form.

Podsols are soils with very low pH values and have experiences high levels of leaching

iron pan / hardpan layers are foud in the B horizon when the soil in deeper layers becomes less acidic

40
Q

What are pedocals?

A

soils with very low p/e values

ie semi-arid to arid regions (steppes and deserts)

41
Q

What characterises pedocals?

A

the soil is rich in carbonates which are found in the B horizon (contrasting to iron oxides found in this layer in pedalfers)

42
Q

examples of pedocal soils

A

Chernozems
Chestnut soils
Calcretes (CaCO3 cement)

43
Q

formation of podzols

A

1) High rainfall → leaching.
2) Leaching of ions (calcium)
3) Acidity, and wetness facilitate mor humus formation.
4) Release of organic acids during decomposition of peaty materials (e.g. fulvic acids).
5) Organic acids attack clay structure by extracting iron and aluminium.
6) Organic acids form complexes (chelates) with Al and Fe and make these metals soluble.
7) Organic matter and decomposed clay also become soluble and are washed out together
with metal chelates.

44
Q

what are the 2 types of zonal soils?

A

pedalfers and pedocals

45
Q

what are zonal soils?

A

soils that are climatically derived and are usually widespread around the earth. Their formation is can be explained due to predominant climatic conditions

46
Q

what are intrazonal soils?

A

they are local variations of zonal soils which are influenced by parent rock type and drainage

47
Q
A

Biogeochem - Ernest (9 decks)

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