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Soil And Water > Extra Reading > Flashcards

Extra Reading Flashcards

1
Q

Hydrophobicity:

Commonly associated with fungal mycelia

A

Savage et al, 1969

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2
Q

Hydrophobicity:

Bug fires vaporise more organic compounds creating a stronger, more continuous hydrophobic layer.

A

Tiedemann et al, 1979

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3
Q

Hydrophobicty:

Stronger in coarser textured soils.

A

Huffman et al, 2001

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4
Q

Infiltration:

Infiltration capacity is a control of surface runoff.

A

Horton, 1933

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5
Q

Infiltration:

Wind action and differential temperatures aid in re-opening soil pores after rain.

A

Horton, 1933

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6
Q

Infiltration:

Increase of infiltration capacity immediately following cultivation of soils.

A

Horton, 1940

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7
Q

Infiltration:

Rough surfaces may have lower infiltration capacities.

A

Horton, 1940

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8
Q

Infiltration:

4 tension disc experiment on loamy soils.

TDR measured water at depth of 2cm below tension disc, with varying hydraulic head.

Measuring transport of contaminants.

A

Simunek et al, 1999

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9
Q

Unsaturated zone:

Part of the soil where water contents are less than the soil porosity.

A

Nielsen et al, 1986

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10
Q

Unsaturated zone:

Surface and ground waters are linked by the unsaturated zone

A

Nielsen et al, 1986

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11
Q

Hysteresis:

Enhanced by presence of rapped air, soil shrinking and swelling and rates of wetting and drying

A

Davidson et al, 1966

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12
Q

Hysteresis:

Keeps water contents higher in the initially wetted part of the soil, while reducing wetting front in the drier soil

A

Dracos, 1984

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13
Q

Unsaturated zone:

Temperature effects viscosity and surface tension.

A

Nielsen et al, 1986

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14
Q

Preferential flow:

In well structured soils, water moves along cracks

A

Bouma, 1991

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15
Q

Preferential flow:

Sandy soils create ‘fingers’

A

Hillel, 1987

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16
Q

Preferential flow:

Dyes used to trace flows but are destructive and you cannot do repeats.

A

Ehlers, 1975

Flury et al, 1994

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17
Q

Preferential flow:

Penetration depth is deeper in wet soils

A

Flury et al, 1994

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18
Q

Preferential flow:

Structure must be considered when pesticides are used.

Poor structure, sandy soils are more susceptible.

A

Flury et al, 1994

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19
Q

Influences on water movement in soils

A

Soil bulk density
Soil strength
Soil OM
Soil chemical properties

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20
Q

Processes that slow infiltration capacity…

A 
Deterioration of soil structure
Crust formation
Detachment of particles(blocked pores) 
Clay swelling
Air entrapment below wetting front
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21
Q

Factors influencing infiltration…

A

Topography
Macropores
Hysteresis

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22
Q

Effects of soil properties on infiltration…

A

Water content - infiltration is faster on initially dry soil

Soil texture - reduced infiltration on fine textured soils - associated with porosity.

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23
Q

Infiltrability depends on…

A 
Time of event
Initial soil water content
Hydraulic conductivity
Soil surface
Presence of impeding layers.
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24
Q

What is field capacity and what is the UK matric potential value used for it?

A

The water content of the soil after it has been saturated and allowed to drain against gravity for 48 hours… Half wet, half dry.

Matric potential -5kPa

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25
Q

Factors effecting field capacity…

A 
Texture
Type of clay-montmorillonite has high fc.
Organic matter
Depth of initial wetting
Impeding layers
Evaportranspiration
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26
Q

What is bulk density… Including the equation.

A

The mass of dry soil per unit of volume (including pore space)

Pb = Ms/Vt
Where ms is mass of solids and vt is total vol.

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27
Q

What happens to bulk density when the ground is compacted?

A

There is less pore space, therefore the bulk density is higher.

28
Q

Why does bulk density increase with depth?

A

Pressure.

29
Q

What is the bulk density of clay like?

A

Clays have low bulk density because of their many micropores

In agricultural soils: 1.00-1.60gcm3

30
Q

What is the bulk density of sands like?

A

Sands have a higher bulk density because all the partials lie close.

In agriculture soils: 1.20-1.80gcm3

31
Q

Pore sizes…go.

Luxmoore 1991

A

Micropores: 100 micrometers

32
Q

What is soil water potential?

A

Potential energy possessed by water held in any position within the soil.

The difference in energy levels determines direction and rate of flow.

High energy state when pore sizes are small.

33
Q

What is water flow in soils caused by?

A 
OM
Chemistry
Topography
Structure
Stoniness
Horizons
Compaction
34
Q

What is runoff influenced by?

A 
Soil type
Cracks
Type of rock
OM content
Vegetation
Topography
Type or rainfall/intensity
35
Q

What is overland flow?

A

If the rate of water supply at the soil surface exceeds the infiltration capacity.

Laminar flow=shallow/gentle
Turbulent flow=erosive

36
Q

What is through flow?

A

Lateral downslope movement within the soil profile.

Diffuse flow (slow)
Macropore flow (fast)
Pipe flow (much larger scale)
37
Q

What is groundwater flow?

A

Need knowledge of parent material including pressure, density, viscosity and homogeneity.

38
Q

What is Channel precipitation?

A

Less than 5% contribution to runoff.

39
Q

Environmental implications of runoff…

A 
Pesticide pollution 
soil loss
flooding
decrease in soil quality
Landslides
Toxic waste
40
Q

What does hydrograph separation enable you to do?

A

Enables separation of runoff compartment from baseflow compartment.

From where runoff begins to the corresponding point on the regression limb.

41
Q

What are the two main hydrographic separations in runoff?

A

Theoretical separation

Experimental separation - using tracers to find water source (isotopic and geo chemical separation)

42
Q

Factors effecting the shape the hydrograph

A

Climate - rainfall intensity. Regression limb would be more gradual and slow for snow.

Topography - size/shape of basin. Slope of land.

Ponding/storage

Geology.

43
Q

What is tortuosity?

A

The average ratio of the actual roundabout path to the straight flow path.

Wiggly line : straight line

44
Q

Pressure cell for measuring matric potential

A

Good to -98kPa, takes a long time to reach equilibrium, works by applying positive air pressure

45
Q

Pressure plate for measuring matric potential

A

Good to -1500kPa, often used in labs, unsuited for large cores and determination at the wet end of the range

46
Q

Psychrometer to measure matric potential

A

Psychrometer: Range -98 to -3000kPa, measures contribution of matric and osmotic potential

47
Q

Tensiometer to measure matric potential

A

Good to -85kPa, inexpensive and quick can measure whole profile but slow to respond/equilibrate, requires excellent soil contact

48
Q

How does a tensiometer work?

A

Water is drawn into soil through porous cup until the pressure in the cup & soil are in equilibrium (Bouma, 1981)

49
Q

Advantages of using a tensiometer to measure unsaturated hydraulic conductivity

A
  • Inexpensive
  • Quick
  • Variable length so can measure whole profile
  • Can be used to control irrigation schedules for crops
50
Q

Disadvantages of using a tensiometer to measure unsaturated hydraulic conductivity

A

Doesn’t measure matric potential as low as PWP, effective up to -85kPa
• Slow to respond/equilibrate
• Requires excellent soil contact

51
Q

Unsaturated hydraulic conductivity decreases as:

A

Volumetric water content decreases
Tortuosity increases
Cross-sectional area of water flow decreases
Drag forces increase

52
Q

Advantages of TDR - measuring unsaturated hydraulic conductivity

A

Fast, precise, non-destructive measurement (Roth et al., 1990)
•Minimal calibration
• Continuous measurement/automation – rapid results

53
Q

Disadvantages of TDR - measuring unsaturated hydraulic conductivity and porosity

A

Measurement area only a few cm’s beyond probe

Problems with clay soils and organic soils

54
Q

Neutron probe to measure soil water content. Porosity.

A

Measures how fast neurons are converted to slow neutrons is dependant on soil water content

55
Q

Advantages of neutron probe

A

Non destructive

High precision

56
Q

Disadvantages of neutron probe

A

Expensive

Health hazard - need training

57
Q

What can be used to measure the water content of a soil

A

Oven drying: 105 degrees for 8 hours

Neutron probe

Time domain reflectometry

58
Q

What would you use to hydrostatic (positive pressure potential) of saturated soils

A

Piezometer

Open tube in soil
Bottom is perforated to allow soil water to enter
Digital reading

59
Q

What would you use to matric potential of unsaturated soils

A

Tensiometer

Water drawn into soil through porous cup until pressure in the cup and soil in equilibrium

60
Q

Name the two flow types in saturated flow

A

Steady state flow - intensity does not change

Transient flow - does change with time, realistic

USE DARCYS LAW TO MEASURE

61
Q

Darcy’s law

A

The flow of water in soils is proportional to the hydraulic conductivity (ease of flow)

The flow of water is dependant on the differences in hydraulic potential between two locations in the soil

The rate of flow is equal to hydraulic conductivity multiplied by hydraulic head.

62
Q

Limitations of Darcy’s law

A

Steady flow - flux must remain constant

Uniform medium - assumption

Preferential flow - no account for horizons and a change in flow due to structure etc.

63
Q

How can hydraulic conductivity be measured

A

Calculated using a permeameter, hydraulic head needs to stay constant

Remember lab work.

64
Q

Factors control Ksat

A

Porosity
Tortuosity
Pore size distribution - poiseuilles law - total flow rate is proportional to R4. A sand with large pores may have a higher Ksat than clay with small pore.

65
Q

Measuring infiltration

A

Double ring infiltration-2 rings with water ponded inside, measurement of rate from inside ring, outside used to reduce lateral flow.

Sprinkle infiltrometers-excess water is sprayed on the surface at a measured rate and runoff independently collected. Pop for catchments studies

Tension disc infiltrometer-water held at tension. Determines unsaturated hydraulic conductivity

Pressure ring infiltration.

66
Q

Hydrophobicity:

caused by leaching of hydrophobic compounds, such as aliphatic hydrocarbons from the litter and humus layers.

A

Huffman et al, 2001

Soil And Water (1 decks)

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