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GEOG 305 Final > Lecture 16-19 > Flashcards

Lecture 16-19 Flashcards

1
Q

What are the 3 types of salt enrichment?

A

Rainwater
Groundwater
Artificial (irrigation)

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2
Q

How does groundwater salt enrichment work?

A

Water moves upward through capillary rise and leaves behind salts as water evaporates

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3
Q

Why is salt enrichment prominent along river and lake oasis in dry and arid regions?

A

Water moves up with capillary fringe

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4
Q

How does salt enrichment through irrigation happen?

A

Occurs on surface but also subsurface of soil

Water percolates quickly after wetting but also evaporates in soil layers –> creates subsurface salt enrichment

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5
Q

What are Sabakh soils (morning soils)?

A

Attract water from fog and dew in the morning –> enriches the soil surface with salt

Creates darker colour as salt enriched soils become saturated by water from atmosphere (during the day as it dries, soil gets more white)

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6
Q

Are salt crusts good a retaining soil moisture?

A

Yes, because crust will dry rapidly however inside will remain wet for longer

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7
Q

How do we measure salt enrichment?

A

Measuring electric conductivity (ECe)
- measured by difference in electrostatic potential
- larger than 15 mS/cm –> salt enriched soil

Measuring sodium adsorption ratio (SAR)

Measuring exchangeable sodium percentage (ESP)

Basically, measure sodium and compare it with other cations present in the soil

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8
Q

How does high salt content impact plants?

A

Induces physical drought due to osmotic potential (drought stress)

Toxic concentrations of certain ions (Boron or chloride toxicity)

Induces unfavourable nutrient ratios (K/Ca)

Influences soil physical properties (change of soil structure, compaction, etc.)

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9
Q

What are some very salt-sensitive crops?

A

Fruits, nuts, citrus, avocado

ESP=2-10

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10
Q

What are tolerant and very tolerant crops?

A

Wheat, cotton, alfalfa, tomato (ESP=40-16)

Some grasses (ESP>60)

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11
Q

What is a typical symptom are stress caused by salinity?

A

Plant loses green colour

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12
Q

What is a human-induced salt enrichment issue in Quebec?

A

Salting the roads during the winter

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13
Q

What is the solubility sequence of salts in increasing order?

A

CaCO3 (calcium carbonate)
NaHCO3 (sodium bicarbonate)
Na2CO3 (sodium carbonate)
CaCl2 (calcium chloride)
KCl (potassium chlroride)
MgCl2 (magnesium chloride)
NaCl2 (sodium chloride)

however this depends partly on temperature

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14
Q

Why is it mrore problematic when a salt is more soluble?

A

Bad for plants due to osmotic potential

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15
Q

What type of soil develops from the accumulation of calcium carbonate?

A

Calcisol

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16
Q

What type of soil develops from the accumulation of calcium sulfate?

A

gypsisol

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17
Q

What type of soil develops from the accumulation of sodium chloride?

A

solonetz

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18
Q

What type of soil develops from the accumulation of other salts?

A

solonchak

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19
Q

What type of soil develops from the accumulation of silicon dioxide?

A

durisol

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20
Q

Solonchak soil

A

Experiences accumulation of salt on topsoil

High water table –> capillary fringe brings groundwater up to the surface –> salt from groundwater evaporates at the surface

High soluble salt content and soil water conductivity

Sources of salt include parent material, residual as water evaporates, coastal salt spray, groundwater

Low OM content due to limited plant growth

Usually well-structured soils because high salinity promotes flocculation

pH generally 7 to 8

Limited agricultural value because of high salinity

Fairly distributed in the world, but mostly found in inner land of central asia and North African prairies

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21
Q

What are the soil forming processes of solonchaks?

A

Usually in inland areas where evapotranspiration is considerably greater than precip.

Differentiation between external and internal solonchack
- salt acc. on surface –> external
- salt acc. at depth –> internal

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22
Q

How are solonchaks managed?

A

Salt has to be leached from soil for good yields
- can be done by irrigation
- However, the problem is that the irrigation water itself contains too much salt which aggravates the problem

If a lot of water present, it can be sufficient to leach out salts from soils

Planting crops with deep rooting system so it reaches the water table and lowers it
- able to reduce effect of groundwater salt enrichment

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23
Q

What is solonetz soil?

A

Poorly structured impervious surface layer

Natric subsurface horizon (high Na concentration)
- shows a ESP of 15 or greater in the upper 40 cm of the horizon

Columnar subsoil structure with clay translocation
- translocation occuring due to presence of Na

In the dry season:
- formation of cracks
- accumulation of salts due to capillary rise of water

In the wet season:
- peptization of clay and OM due to high Na concentrations in upper soil horizons
- illuviation of clay and OM in the Btn horizon

Found in Australia and middle east

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24
Q

What is soil dispersion caused by?

A

High Na and low salt levels in sodic soils can cause clay dispersion, degradation of aggregate structure and loss of macroporosity

If there is sufficient amount of water in usually dry season, topsoil becomes saturated –> high Na content leads to dispersion of clay and OM, destroys soil aggregate and forms soil crust on surface impeding plant growth

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25
Q

How do hydrated ions affect bonding forces ?

A

No hydrated ions: colloid are bound by van der walls forces

Hydrates ions can go between colloid and weaken van de waals forces

hydrated Na ions prevent binding of colloid because of loosely bound Na ions which pull colloid away (no more van der waals forces)

Results in dispersion of microstructure of soil and soil aggregates

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26
Q

What are calcisols?

A

Accumulation of calcium carbonate typically in subsoil

Not very soluble there fore still allow for some crop growth

Accumulation occurs beacuse:
- CaCO3 dissolves in topsoil –> leaches –> precipitation of secondary carbonate at deeper soil layers
- Leaching into groundwater –> capillary rise –> precipitation of carbonates in soils

Mostly found in arid and semi-arid regions such as Northern Africa and Middle East

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27
Q

What are calcisols used for?

A

Used for grazing

If precipitation exceeds 400 mm/yr, rainfed agriculture with drought tolerant crops such as wheat or sunflower is possible

When irrigated, calcisols allow the production of a wide range of fruits, grain and fodder crops

Careful irrigation is necessary to prevent salinization
- The topsoil of calcisols is easily eroded. Where this topsoil is lost, the calcic horizons exposed to the surface form calcrete crusts (rock solid)

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28
Q

How to remove salts from soils?

A

Addition of irrigation water removes soluble salts but leaves cation exchange complex dominated by Na

Na leads to dispersion and poor soil structure

Na combines with carbonic acid in soil solution producing Na2CO3 and raising pH (strong base weak acid)

Whilst removing soluble salts, add CaSO4 (gypsym)
- Ca preserves flocculated structure
- excess Na removed as neutral Na2SO4 (strong base strong acid)

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29
Q

Aridisol (desert soil)

A

Almost complete absence of water –> creates desert pavement of gravel

Old, oxidized, Fe-rich horizon
- have developed in geologic past when soil was exposed to more rainfall

Silcrete (Si-cement horizon)
- Silica cementation

Desert pavement of gravel

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30
Q

what are desert soil processes?

A

Sparse vegetation and rapid decomposition after rainfall leads to low OM content of soils
- no plant cover = a lot of erosion (fluvial or aeolian)

Dev. of stone pavement on surface, either through aeolian or fluvial erosion of fine particles

Dominance of previous soil formation processes, especially in pluvial periods during Pleistocene
- Fe-rich material –> red colour
- CaCO3 acc. –> caliche
- silica cementation leads to silcrete

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31
Q

How come we can find islands of vegetation in deserts?

A

Created by onset of vegetative cover

Over time, vegetative cover can become larger and create prockets of more fertile and better at retaining soil water

Because acc. of OM, and vegetation cover, lower evaporation and enhanced soil water and nutrient availability

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32
Q

What are organic soils (histosols)?

A

Organic material accumulates in wet places where plant growth exceeds the rate of residue decomp.

In such areas, residues accumulate over the centuries from wetland plants

Possess very high capacities to hold water and cations
- higher than clay-rich mineral soils on a weight basis, but similar to mineral soils rich in 2:1 silicate clays when considered on a volume basis (water or cations held per liter of soil)

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33
Q

Where are peatlands found?

A

Abundant in the North (places with wet and cool conditions that allow acc. of OM)

Some tropical peatlands exist nonetheless

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34
Q

What causes OM to accumulate in organic soils?

A

Litter input eventually reaches anaerobic zone in soil profile (below water table). Decomp. rates under anaerobic conditions are 20 times slower than under aerobic conditions

Some wetland plants have slow inherent decomp. rates (produce biomass that have slow deomp. rates –> internal resistance of material)
- shrubs, sedges, tree leaves, mosses

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35
Q

What are the 4 types of peat materials?

A

Type of peat depends on the vegetation that contributes to the OM

1) Moss peat: the remains of mosses such as sphagnum

2) Herbaceous peat: residues of herbaceous plants such as sedges, reeds, and cattails

3) Woody peat: from the remains of woody plants, inclduing trees and shrubs

4) Sedimentary peat: remains of aquatic plants (algae) and of fecal material of aquatic animals

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36
Q

Explain the development of a peatland

A

Onset of peatland dev. from a pond or lake
- hollow filled with water, there are some plants on the edges as well as some aquatic plants

Accumulation of OM on the pond floor
- the dead biomass will fall down and will reach the bottom of the lake in anaerobic conditions

Infilling of pond with OM and dev. of peatland veg.
- accumulation of OM slowly starts to fill the hollow

Fomes bog with drainage impedance and paulidification
- vegetation will start to grow on top of OM
- the parent material in the top part of the soil is completely disconnected from the mineral layer on the bottom
- OM is building the parent material

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37
Q

What is terrestrialization?

A

Growth of OM inwards

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38
Q

What is paludification?

A

Growth of OM outwards

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39
Q

What directions does peat grow?

A

Bottom to top
Outwards
Inwards

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40
Q

Bogs vs. fens

A

Bog is raised above mineral layer, therefore the inflow of water only goes into fen layer

Dev. of fen is still in contact with mineral soil, therefore inflow of water in valley leads to accumulation of fen peat

41
Q

What are the 3 types of organic soils in Canada

A

Fens: mainly in arctic/subarctic regions, usually 50-200 cm think
- usually minerotrophic

Bogs: primarily in boreal zone, up to 600 cm thick
- often ombrotrophic

Swamps: mainly in temperate zone, 100-200 cm thick
- can be omrbotrophic or minerotrophic

42
Q

Minerotrophic definition

A

Nutrition is mineral rich since mineral from mineral soils are transported to fens –> more fertile for plant growth

43
Q

Ombrotrophic definition

A

Peatland surfaces that are supplied only with rain and snow (atmospheric deposition)

44
Q

What are the characteristics of swamps?

A

Vegetation: trees and shrubs

Hydrology: topography controlled, waterlogged in the spring, dry in the summer

Acidity: variable (5-7)

Rate and degree of decomp.: fast and high (mainly humisols and mesisols)
- dry summer –> higher decomp. rates

Utility: when drained, high crop production (vegetables)

45
Q

What are the characteristics of fen?

A

Vegetation: sedges and shrubs

Hydrology: topography controls drainage, usually flowing water throughout the year, can be rich in bases

Acidity: moderate pH (5-6.5)

Rate and degree of decomp.: medium, moderate (fibrisols and mesisols)

Utility: none

46
Q

What are the characteristics of bogs?

A

Vegetation: mosses and trees (and shrubs)

Hydrology: low hydraulic conductivity of humified horizons, depends on rainfall (no inflow from river or groundwater)

Acidity: very acid (<5)

Rate and degree of decomp.: slow and low (mainly fibrisols)

Utility: production of peat moss and peat for energy

47
Q

Is the oxic zone below or above the water table?

A

Above, it goes oxic zone –> oscillating water table (varies between summer and winter) –> anoxic zone

48
Q

How does the minerotrophic layer get nutrients vs. ombrotrophic layer?

A

Minerotrophic: in contact with mineral layer and rich in mineral nutrients

Ombrotrophic: from wet and dry deposition (soil dust, anthropogenetic input, ashfall, marine aerosols)
- above water table, therefore runoff never flows in there

49
Q

What happens to methane emissions as water table rises closer to the surface?

A

CH4 emissions increase

50
Q

Is the top layer of peat alive of dead biomass?

A

Combo of alive and dead root biomass –> transition from living biomass into decomposed biomass

Acrotelm: transition from living biomass to dead biomass (transient carbon storage)

Catotelm: permanent anoxic conditions (long-term storage)

Note: cotton grass roots are deep enough that they go beyond the catotelm layer (can access nutrients beyond)

51
Q

Explain the carbon budget of peatlands

A

Vegetation takes up CO2 through photosynthesis (input)

Plant/microorganisms respire CO2 back into the atmosphere (output)

Decomposition produces CO2, CH4 and dissolved organic carbon (output)

52
Q

Why do peatlands have a negative C budget?

A

Exchange of CO2 (uptake through photosynthesis, release through respiration/decomposition)

Emission of methane (CH4) to the atmosphere under anaerobic conditions

Export of dissolved organic carbon from decomposition of OM

Imbalance of C uptake vs. loss leads to long-term C accumulation –> significant reduction in atmospheric CO2

53
Q

Explain the carbon cycle in peatlands

A

Plants take from atmospheric CO2:
- aeorobic degradation in the acrotelm –> CO2 emissions back into the atmosphere
- anaerobic degradation

Peat in catotelm
- releases CH4 from the catotelm that oxidizes in the acrotelm and releases CH4 to the atmosphere
- releases CO2 that oxidizes in the acrotelm and releases CO2 to the atmosphere

54
Q

What is the Eddy covariance tower used for?

A

Used to measure CO2 fluxes

Continous measurements of water, energy and CO2 and CH4 fluxes

55
Q

Explain the net ecosystem exchange (NEE) of CO2 throughout the year

A

NEE is positive in the autumn/winter months because there is no photosynthesis (outflow of CO2) –> increases

In april, we still have an increase despite photosynthesis beginning since decomp. rates are still higher (decomp. strong due to warming temperatures) –> april is the peak positive value of NEE

May and onwards, plant cover increases –> fluxes of CO2 begins to go the other direction (NEE is negative)

Around July, there is a tipping point –> system taking up more CO2 and stored in peatlands (more inflow than outflow)

Afterwards, NEE negative until stabilizes
- measurements are very dispersed due to accumulated uncertainties

56
Q

Explain the changes in concentrations of calcium with varying precipitation rates

A

High rainfall: Ca will be dissolved and washed out
- low concentrations

Threshold of about 2000 mm/yr: water balance is not enough to leach it out
- sharp increase

Decreases when rainfall is too low since plants are limited
- concentrations decrease

57
Q

Explain the changes in concentrations of phosphorus with varying precipitation rates

A

High rainfall: leached and mobilized
- low concentrations

Threshold of about 2000 mm/yr: decreased rainfall means that soil dev. is not as dominated by allophanes therefore larger amount of P

Decreases when rainfall is too low

58
Q

What happens to soil pH when rainfall increases?

A

It decreases

59
Q

List a few important GHGs

A

Water vapour (H2O
Carbon dioxide (CO2)
Methane (CH4)
Carbon monoxide (CO)
Nitrous oxide (N2O)
Nitric oxide (NO)
Ozone (O3)

60
Q

What GHG has the highest residence time?

A

N2O>CO2>CH4

61
Q

What is the GHG with the highest concentration in the atmosphere currently?

A

CO2>CH4>N2O

62
Q

What GHG has the highest radiative absorption potential?

A

N2O>CH4>CO2

Nitrous oxide is therefore dangerous due to its long residence time and radiative absoprtion potential

63
Q

Why are CO2 emissions lower in the Northern hemisphere?

A

More land mass, therefore more potential for photosynthesis

64
Q

What was the dominant source of annual CO2 emissions until 1950? What is it now?

A

Before, it was land-use change
Now, it is bruning of fossil fuels

65
Q

What are important carbon sinks?

A

Land sinks (soil): taken up by vegetation and stabilized in soil

Ocean sinks

66
Q

What are some contributors to carbon emissions?

A

coal, oil, gas, cement, land-use change, etc.

67
Q

What is the effect of land use change on soil carbon?

A

Temperate forest: loss of 34% of soil carbon

Temperate grassland: loss of 29% of soil carbon

Tropical forest: loss of 21% of soil carbon

Tropical grasslands: 46% of soil carbon

68
Q

How much carbon is loss from agricultural conversion a year?

A

Approx. 0.1-5 Pg C/yr

Therefore, return of agricultural land to forest will increase soil C

69
Q

Why are land-use change emissions declining?

A

Transfer of croplands to forests/grassland ecosystems

Management practices have been improved (low tillage, de-intensification of production)

70
Q

What type of soil stores the most carbon?

A

Histosols

71
Q

Why are SOC stocks highest in higher latitudes even though above ground carbon in vegetation is small?

A

Because decomposition processes in cold regions is slow which is why SOC accumulates

Warming temps may lead to oxidation of huge amount of carbon stored in higher latitudes

72
Q

What happens to C sequestration when there are changes in SOM?

A

Most natural ecosystems appear to be in equilibrium with SOM content: input=output

Rates of C sequestration of initially high as ecosystem develops, then fall to low values as ecosystem reaches equilibrium

Example: tropics are very old and very large C sequestration with a lot go vegetation, but also a lot of leaching of DOC and a lot of decomposition

The exception to this pattern: wetlands
- decay is OM is slowed by anaerobic and cold conditions
- most northern peatlands have accumulated OM and appear to be continuing
- therefore, peatlands are major terrestrial sink of CO2 since deglaciation 10,000 yeras ago

73
Q

How can be increase C sequestration in soils?

A

Increase rate of input of OM into soil
- change land use to higher NPP
- leave plant material on soil surface
- convert cropland to pasture and pasture to forest
- change tillage practices

Reduce rate of decomp. in soil or increase ability of soil to adsorb and retain SOM

C sequestration greatest where NPP enters soil from roots and where soil either cold, anaerobic or clay-rich, which slows down rate of decomp.

73
Q

How can be increase C sequestration in soils?

A

Increase rate of input of OM into soil
- change land use to higher NPP
- leave plant material on soil surface
- convert cropland to pasture and pasture to forest
- change tillage practices

Reduce rate of decomp. in soil or increase ability of soil to adsorb and retain SOM

C sequestration greatest where NPP enters soil from roots and where soil either cold, anaerobic or clay-rich, which slows down rate of decomp.

74
Q

What factors are important to assess how global warming will impact vegetation?

A

Depends on effect on NPP of vegetation
- change in temp.
- water availability
- elevated atmospheric CO2
- changes in soil nutrient availability (especially N and P)

Redistribution of vegetation in response to climate change (migration from south towards North?)

75
Q

What are the inputs of OM in soils?

A

SOM = NPP - decomp. - leaching

Litter (plant debris and metabolites, animals carcasses and excrements)

Leachates (throughfall and stemflow containing nutrient ions and soluble organic compounds)

Soil organisms

Roots (rhizosphere detritus and secretions)

76
Q

What happens to the water table during the summer?

A

Water table will lower since there is less rain, less transpiration from vegetation, more evaporation

Soil profile becomes more aerobic –> increase in carbon emissions

77
Q

What happens to the water table during the winter?

A

It will rise and a larger amount of the soil profile will become anaerobic

78
Q

What are methane fluxes controlled by?

A

Soils can be a source of methane under reducing conditions: function of redox potential (Eh)

Methane flux to atmosphere from wetland soils controlled by microbial activity (methanogenesis)

Depends on:
- temp.
- water table position (aerobic vs. anaerobic portion of the soil profile)
- plant cover (some plants act as conduit of methane to atmosphere)

79
Q

What are some mechanisms leading to methane emissions from wetlands?

A

Methanogenesis converts organic carbon from roots and plant tissues into methane in the soil that can be oxidized, diffused, transported out by vascular transport, or bubbled out

80
Q

What is ebullition of methane?

A

Organic compounds are reduced into methane which can bubble out into the atmosphere

81
Q

How can methane be consumed?

A

Can be consumed by methotrophic bacteria in well-drained soils

Rates are small compared to methane emissions from wetlands, but upland soils cover large areas

HOWEVER, consumption rates are reduced by increased N availability in soils (by atmospheric N deposition from fertilizers or combustion of fossil fuels)
- because microbes no longer have a competitive advantage over other organisms when N (limiting nutrient) becomes available

82
Q

What are some sinks of methane?

A

Tropospheric OH
Stratosphere
Soils (well-drained)

83
Q

What are some sources of methane?

A

Wetlands, lakes and freshwater, termites, wildfires, biomass burning, landfills, fossil fuels, geological, ruminents, paddy fields

There are more sources than sinks –> increase in methane in the atmosphere

84
Q

What have humans done to increase methane over the years?

A

Creation of paddy soils and flooded areas (due to hydro-electric dams)

Decreased C sink in upland soils because of increased N deposition

85
Q

What have humans done to decrease methane over the years?

A

Drainge of wetlands soils –> changes from a source to a potential sink

However, this increases CO2 emissions

86
Q

What is the effect of climate change on methane?

A

Methane consumption has very limited dependence on temp. so unlikely to change

Methane production is very temp. dependent so will increase methane flux
- warming will lead to permafrost melting, waterlogging areas and icnreasing methane emission from subarcitc and polar wetlands

However, primary control is water table position: may be lower –> reducing emission rates

87
Q

Where is permafrost found?

A

Mostly located in subarctic and arctic
Also found in rocky mountains

88
Q

How are abandoned oil/gas wells and pipes contributed to methane fluxes?

A

Abandoned pipe becomes a conduit for deep soil methane to be released into the envr.

89
Q

What is the most potent GHG?

A

Nitrous oxide

90
Q

How are N gases released during nitrification and denitrification in soils?

A

Under anaerobic conditions, N becomes electron acceptor and is reduces to N2 or creates N2O

Therefore, the application of N-rich fertilizers can lead to oxidation and release of N2O and NO
- disturbance could be reduced by more efficient application of N fertilizer

Riparian zones (zones where snowmelt and agricultural drainage ends up) –> hotspots for N2O emissions due to high denitrification

(REVIEW N-CYCLE)

91
Q

What are N2O emissions from soils controlled by?

A

Low O2 contents associated with high water contents
- much more present during denitrification

High temps

Rapid N cycling

Disturbance, through annual crops, forest clearance

Addition of N fertilizers

92
Q

What soils are the biggest sources of N2O?

A

Fertilized soils>tropical forest soils=oceans,estuaries,wetlands

93
Q

Why is nitrous oxide difficult to monitor?

A

Fluxes from natural systems are very episodic (compared to CH4 or CO2)

No real evidence that fluxes will change greatly in response to climate change

94
Q

What is the role of soils in controlling atmospheric concentrations of CO2, CH4 and N2O?

A

CO2: through decomp. of OM and stabilization of SOC

CH4: through methanogenesis under anaerobic conditions and CH4 consumption under aerobic conditions

N2O: through leakage of N cycle

95
Q

How have human activities contributed to increased concentrations of CO2, CH4 and N2O?

A

CO2:
through change in land use converting forests and grasslands to cultivation
- reducing OM content
- drained wetland soils, respired as CO2

CH4:
- through increased flux from rice paddies and other flooded soils
- reduced CH4 consumption in N-affected soils
- reduced emission from drained wetland soils

N2O:
- through increased leakage of N cycle
- from N fertilizer addition and increased disturbance

96
Q

What happens to CO2 and CH4 concentrations when a wetland is drained?

A

Increase CO2 and decrease in CH4

Overall, we still contribute more to GHG effect by draining a wetland

97
Q

How is climate change going to affect CO2, CH4 and N2O emissions from soils?

A

CO2:
- through balance of plant production and decomposition of OM
- A lot of uncertainty –> may lead to positive feedback (accelerate warming)

CH4:
- through change in water table and wetland area
- decrease in temperature and tropical regions but increase in permafrost terrain

N2O:
- unknown effect, likely small

98
Q
A

GEOG 305 Final (3 decks)

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