Earth System Science Snd That Critical Zone Flashcards
(212 cards)
1
Q
what are the systems of the earth?
A
geosphere - rocks
hydrosphere - water
cryosphere - ice
atmosphere - gas
pedosphere - soils
biosphere - ecosystems
2
Q
how do earths systems interact?
A
by transferring energy and mass
3
Q
what is earth system science?
A
the holistic, transdisciplinary understanding of earths components and their interactions
4
Q
what is a system?
A
a group of interconnected parts that interact to function as a complex whole
5
Q
what is a component?
A
individual parts of the system that serve as reservoirs of mass and energy. can function as sub systems
6
Q
what is meant by the state of a system?
A
set of important attributes of the whole system/individual components that characterise the system at a particular time
7
Q
what is meant by equilibrium state?
A
when attributes of a system are not changing with time. can be stable or unstable
8
Q
what is meant by disturbance?
A
changes to the attributes of a system component. ie perturbation, forcing
9
Q
what is meant by coupling?
A
the exchange of mass/energy from one component to another causing attribute changes through the system
10
Q
what is meant by feedback loop?
A
sequence of couplings in a circular looping back to the original system component. can amplify (positive) or dampen (negative) disturbances
11
Q
give an example of a positive feedback loop
A
climate and cryosphere
warm=less ice=less albedo=more radiation absorbed = warmer = less ice
12
Q
give an example of a negative feedback loop
A
warm = increased silicate weathering = increased removal of CO2 from atmosphere = decreased temperature
13
Q
what is the feedback if gradients of functions are in opposite directions?
A
negative
14
Q
how do you calculate the strength of feedback?
A
magnitude of feedback = (dP/dCO2) x (dCO2/dP)
gradient of photosynthesis as a function of CO2
vice versa
15
Q
what is the point at which variables are satisfied by both functions?
A
equilibrium state
the intercept between both functions
16
Q
what causes stable equilibrium states?
A
negative feedbacks
returns system to original state following a disturbance
17
Q
what causes an unstable equilibrium state?
A
positive feedbacks
amplification of disturbances that shifts the system towards a new equilibrium state
18
Q
what is daisyworld?
A
hypothetical world where the only factors that can change are luminosity and albedo (controlled by black and white daisies that have the same optimal temp and habitability)
19
Q
is earth an open or closed system?
A
closed system
20
Q
how do you calculate the inventory of a reservoir?
A
substances concentration x total material mass
express in grams/tonnes
21
Q
what is a flux?
A
exchanges of an element/compound between earth system components
22
Q
what is residence time?
A
the average time an individual atom/molecule spends in a reservoir
inventory/flux
in years
23
Q
what is meant by steady state?
A
when a reservoir inventory does not change with time. calculated as the difference between sum of input and output fluxes.
24
Q
how do you know is a reservoir inventory is increasing or decreasing over time?
A
dInventory/dTime = sumInputs - sumOutputs
if dInventory/dTime > 0 inputs are greater than outputs
if <0 outputs are greater than inputs
25
what is the perturbation rate?
residence time
dInventory/dTime = sumInputs - sumOutputs
26
what is doubling time?
the response of an inventory to a given perturbation
time to double inventory = inventory/perturbation rate
27
how do you calculate how long a reservoir will take to flood?
perturbation rate
scale inventory to max volume using doubling time
28
where is carbon stored?
surface:
atmosphere - 600Gt
ocean - 38,000Gt
critical zone - 2,300Gt
rocks - 100,000,000 Gt
29
what is the residence time of surface carbon?
205 k yrs
30
what is the cumulative carbon transfer from fossil fuels since 1850?
695Gt
31
why is current CO2 atmospheric concentration not as high as calculated?
transfers to the biosphere and ocean
accumalation in the atmosphere
32
what is the critical zone?
everything between unweathered bedrock and the atmosphere
33
what is the upper and lower boundary of the critical zone?
lower = base of freely circulating groundwater
upper = top of vegetation canopy
34
what is the structure of the critical zone?
above ground ecosystems
regolith - soil and saprolite
WATERTABLE
bedrock
35
What is soil defined as in the critical zone?
mixture of altered bedrock and biologically produced material and living organisms
medium that supports almost all terrestrial ecosystems
36
what is saprolite defined as in the critical zone?
physically and chemically altered bedrock. impacted by interactions with surface derived water
37
what is bedrock defined as in the critical zone?
unaltered rock
38
what is the vadose zone?
unsaturated area
soil and saprolites
39
what is the phreatic zone?
bedrock below the water table
40
how thick is the critical zone?
hard to define and difficult to measure
above ground ave 6m, up to60m
unsaturated zone 0-220m, ave 25m
saturated zone 0-140m, ave 7m
41
what affects the depth the critical zone?
above ground - rainforests vs barren
unsaturated - climate and topography
saturated - climate, topography and local geology
42
what is Rn?
net radiant energy
Rn = photosynthesis + evapotranspiration + emission of longwave radiation + heat flux into the regolith
simplified to =evapotranspiration + emission of longwave radiation
43
what are the fluxes of the water cycle?
inputs: precipitation
outputs: evapotranspiration, surface runoff, infiltration, base flow
44
what drives the fluxes of water in the critical zone?
gravitational potential
solar radiation
45
what is the equation for the critical zone water balance?
dWaterStorage/dTime = input from precipitation - (outputs from evapotranspiration + base + surface runoff flow)
46
what are the major flows of mass and energy in the critical zone?
water
CO2
rock derived material
ecosystem nutrient supply
47
What is the photosynthesis equation?
6CO2 + 6H2O <-> C6H12O6 +6O2
48
What is NEE?
Net Ecosystem Exchange
49
how do you calculate the rate of change of critical zone carbon storage?
dCarbon/dTime = photosynthesis- respiration
50
how do you calculate the mass flux of rock?
uplift (g/cm2/yr) = uplift rate x rock density
51
how are rocks transported upwards into the critical zone?
tectonic uplift
52
how is rock derived material removed from the critical zone?
by physical and chemical denudation
53
what is physical denudation?
the loss of solid material from the critical zone by physical erosion
=(river discharge x river suspended sediment concentration)/area
54
what is chemical dunudation?
the loss of dissolved material from the critical zone by chemical weathering reactions
= (river discharge x river water concentration of dissolved solutions)/ area
55
how is land surface change calculated?
dLand surface/dTime = (Uplift rate - (physical + chemical dunudation))/density of uplifted rocks
56
how are nutrients lost from ecosystems?
physical and chemical denudation
volatile species conversion to gases
57
how do you calculate the rate of changing critical zone nutrient storage?
dCZnutrients/dTime = (chemical weathering +atmosphere) - (chemical denudation + physical denudation + atmosphere)
=inputs-outputs
58
what are the benefits of the critical zone?
provisioning
regulating
cultural
supporting/habitat
59
what is a provisional service?
providing materials and energy resources
water storage, food supple
60
what is a regulating service?
Benefits obtained through moderation or control of ecosystem processes
water quality & supply regulation, gas regulation, climate regulation
61
what is a cultural service?
non-material benefits provided to society and culture
recreation, cognitive, aesthetic
62
what are supporting/habitat services?
maintenance of fundamental ecosystem processes
primary production, soil formation, nutrient cycling
63
what is soil?
the biologically active, porous medium that has developed in the uppermost layer of earths crust
64
what is soil made of?
combination of solid material composed of minerals and organic matter, and pore spaces that are occupied by water or air
65
what are primary minerals?
those inherited from the soil by parent rock material
quartz, feldspar, micas, carbonated, pyroxenes, olivine, amphibole
66
what is the composition of soils from primary minerals dependent on?
composition of parent rock
selective dissolution via chemical weathering
67
what are secondary minerals?
those formed within the critical zone through the chemical weathering of primary minerals
secondary phyllosilicates, Fe and Al oxides/oxyhydroxides, secondary carbonates and salts
68
what are clay minerals?
secondary phyllosilicates
Fe and Al oxides/oxyhydroxides
69
what is a secondary phyllosilicate?
clay minerals
kaolinite
smectite
illite
70
what are Fe and Al oxides/oxyhydroxides?
clay minerals
goethite, hematite, gibbsite
71
how are nutrients stored in soil?
nutrient cations (K+, NH+4) substitute for SiO+4 in the octahedral layer of phyllosilicates
72
what is the exchange pool?
negative electrical charges of surfaces must be balanced by the adsorption of cations in the surrounding soil solution
73
what does the adsorption-desorption reactions on clay surfaces control?
plant available nutrient stores
soil pH buffering
filtering of pollutants from water
74
what is goethite?
FeOOH
75
What is hematite?
Fe2O3
76
what is organic matter?/
material composed of organic compounds, ie C-C and C-H bonds
produced by autotrophic organisms that assimilate CO2 from the environment into organic molecules
77
What are the main groups of organic compounds produced by terrestrial plants
cellulose, sugars and starches
fats and waxes
lignin
proteins
78
what is the qualitative field indicator from Soil organic matter?
the darker the soil, the more organic matter there is
79
what are the classifications of soil organic matter?
non humic substances
humic substances
80
what are non-humic substances?
living biomass - roots, fungi, bacteria, worms etc
undegraded dead biomass - cellulose, fats/waxes, lignin, proteins etc
81
what are humic substances?
products of degradation of biomass
organic molecules with poorly defined chemical structures
82
what are the divisions of humic substances?
humic acid - soluble from 7-14 pH
fulvic acid - soluble at any pH
humin - not soluble at any pH
83
why is soil organic matter negatively charged?
abundance of enolic, carboxyl and phenolic groups
84
what does pore space influence?
water storage capacity
soil drainage
soil aeriation - exchange of gases between soil pores and the atmosphere
provides space for biota
85
what are the characteristics of dry soil pores?
good aeriation = rapid gas exchange
little water available for plants
86
what are the characteristics of water saturated soil pores?
lots of water for plants
poor aeriation = slow diffusion of gases
87
what are the requirements for aerobic respiration?
O2
88
how is porosity calculated?
=volume pores/total volume x 100
=density bulk/density solid x100
89
what is density solid?
bulk density of the soil solid material
2.66g/cm3
90
what is density bulk?
bulk density of soil including both solid and pore space components
91
what are the pore size classifications?
from smallest to largest
cryptopore <0.1µm
ultramicropore 0.1-5µm
micropore 5-30µm
mesopore 30-75µm
macropore >75µm
92
what are the implications for drainage and water retention based on pore size?
macropores - drains readily by gravity
mesopores+micropores - water held by capillary pressure and is plant accessible
ultramicropores+cryptopores - water held too tightly by capillary pressure that is not accessible by plants
93
what are the grain size classifications of soil textural properties?
fine earth <2mm (sand slit clay)
coarse fragments >2mm (pebbles cobbles boulders)
94
what is the composition of sands and silts?
dominated by primary minerals
produced by physical disaggregation of parent rock
95
what is the composition of clay fractions?
dominated by secondary minerals
produced by chemical precipitation
96
what are the water characteristics of sand?
good drainage
good aeriation
poor water retention
97
what are the water characteristics of clays?
poor drainage
poor aeriation
good water retention
98
what are the water characteristics of loams?
(mixture of sand slit and clay)
balance between drainage, aeriation and water retention
99
how do aggregates occur?
attraction of electrostatic forces between charged minerals, organic matter and soil solution cations
cementation by CaCo3/gypsum precipitation
100
what is the characteristic of aggregates?
creation of a soil structure with a range of pore sizes that allow a good balance between aeriation, drainage and retention
101
what are the two types of aggregate?
interaggregate - micropores, good for retaining water
intraaggregate - macropore, facilitate pathways from drainage and aeriation
102
what are the types of soil structure at macro scale?
singular grains
granular
prismatic
platy
blocky
massive
103
with reference to composition, texture and structure, explain how soil is a medium for plant growth
soil exchange pool controlling nutrient availability and soil pH
micropores and macropores allowing water storage and soil aeriation
104
with reference to composition, texture and structure, explain how soil functions as water storage, supply and purification
micropores and macropores allow storage and drainage respectively
texture and structure controls infiltration rate
adsorption of metal cations and persistent organic pollutants onto clay and soil organic matter surfaces allows the purification of pollutants
105
with reference to composition, texture and structure, explain how soil influences atmospheric composition
Soil organic matter is a major store of carbon from the atmosphere
soil aeriation/drainage influences soil pore O2 concentrations and therefore soil organic matter respiration rates and metabolic patheays that produced CO2, CH4 and N2O
106
with reference to composition, texture and structure, explain how soil provides habitats for organisms.
soil structure and texture + aggregate formation allow pore spaces
107
with reference to composition, texture and structure, explain how soil is a medium for engineering
soil structure/texture including aggregate formation gives soil stability
amount and type of phyllosilicates in the soil controls swelling and desiccation
108
what are the major reservoirs of water?
groundwater - 630,000km3
lakes - 220000km3
soil moisture - 54,000km3
reservoirs - 11,000km3
rivers - 2,000km3
biomass - 1,000km3
109
what is green and blue water?
green water = supply for plant growth ie soil moisture
blue water = store for human water use ie groundwater
110
what are the possible pathways for precipitation?
1. directly reach soil surface
a)lost via evaporation, b)lost via surface runoff, c)enter soil pores by infiltration (ci. drainage through macropores to groundwater, cii. uptake into plants via roots, ciii. loss to atmosphere via transpiration )
interception by plant cover (return to atmosphere by evaporation)
111
what can happen to water after entering groundwater via drainage?
a) exit via lateral flow and input to river channels
b) re enter soil moisture zone via capillaries (can then be lost to transpiration)
112
what are the fluxes of critical zone water?
inputs:
precipitation
capillary rise
outputs:
evaporation (of intercepted precipitation, from soil surface)
surface runoff + baseflow
infiltration
drainage to groundwater
uptake by vegetation + loss by transpiration
113
how do you calculate soil moisture balance?
dSoil moisture/dTime = (precipitation + capillary rise) - (evapotranspiration + drainage + runoff)
114
what is water movement driven by?
gradients in potential energy
high - low pressure
115
what is water potential?
potential energy of water per volume - equivalent to pressure
measured in J/m3 =Pa
= reference state + gravitational potential energy + matric potential energy + osmotic potential energy
116
how is gravitational water potential calculated?
= gravity x height difference x density of water
117
what is the density of water?
1000 kg/m3
118
what allows water molecules to form inter-molecular bonds?
polarity
bonds with other water = cohesion
bonds with particle surfaces = adhesion
bonds with ions dissolved in solution = osmosis
119
what is matric potential?
the amount of energy required to overcome adhesive forces and move water away from particle surface
increased attractive force = more negative matric potential
120
what are the classes of soil moisture?
permanent wilting point
field capacity
saturation
121
what is osmotic potential?
polar water molecules form solvation spheres with dissolved ions in solution
more attracted to areas with higher dissolved solutes
122
what is water use efficiency?
amount of biomass produced per unit of water used by a plant
123
what is the typical water use efficiency?
1-5g CO2 per 1kg of water
124
what are the soil moisture regimes?
aridic - dry all year round
xeric + ustic (grasslands, savannahs, shrublands) - wet and dry season
udic + perudic (forests)- wet most of the year
interfrost - seasonal freezing and thawing of soil moisture
permafrost - soil moisture frozen most of time
125
where is cropland typically centred?
on udic soil moisture regimes - soil moisture levels are sufficient to sustain plant growth all year
exceptions : india(ustic), southern+eastern europe (xeric)
126
why is irrigation required for xeric soil moisture regimes?
low precipitation + high evapotranspiration during summer = deficit in natural soil moisture needed for high crop yields
127
what is the impact of irrigation?
removal of water from groundwater reserves faster than it can be recharged
128
what acids are involved in chemical weathering?
weak acids, min pH 4 :
carbonic acid H2CO3 - derived from dissolution of atm CO2 in surface waters
Organic acids ie oxalate acid H2C2O4 - derived from atm CO2 via photosynthesis
strong acids :
sulfuric acid H2SO4 - produced from oxidation of sulphide
nitric acid HNO3 - produced by oxidation of ammonia
129
what is the rate of dissociation dependant on?
solution pH
lower pH = reactions shift to the left, releasing less protons
lowest pH possible is 4 for weak acids
130
what are the reactants of chemical weathering?
primary minerals + water and atmospheric gases
131
what are the products of chemical weathering?
dissolved solutes (exported from Critical zone by water)
secondary minerals (made by secondary chemical reactions)(accumulate in soil)
132
what are immobile elements during chemical weathering?
Fe and Al
quantitatively reprecipitates as phyllosilicates (Al, Fe) or Fe oxyhydroxide minerals (Fe)
Si (phyllosilicates)
133
what are mobile elements during chemical weathering?
Ca , Na , Mg, K - base cations
dominate dissolved cation budget of rivers
do not reprecipitate
fraction contained in phyllosilicates
134
how is the residence time of primary minerals in the critical zone calculated?
= depth of critical zone (m) / uplift rate (m/yr)
135
explain the journey of rocks in the critical zone through their residence time
1. primary minerals enter the base of the CZ by uplift or downward migration of the weathering front
2. primary minerals transit through CZ and are subjected to chemical weathering, breaking them down and converting them to secondary minerals
3. dissolved products are exported via rivers/groundwater flow
4. remaining primary minerals and produced secondary minerals are removed via erosion at soil surface
136
what are the controls on chemical weathering rates?
rate at which fresh primary minerals can be supplied to the critical zone by uplift/denudation
rate at which primary minerals undergo weathering
mineralogy, uplift/erosion rate, surface area, climate, biology
137
what is meant by supply and kinetic limited chemical weathering?
supply limited:
mineral supply to CZ < reaction kinetics within CZ
chemical weathering rate = mineral supply rate into CZ
Kinetic limited:
mineral supply to CZ > reaction kinetics within CZ
chemical weathering rate < mineral supply rate
138
what are the primary and secondary minerals of granite?
primary: quartz, plagioclase, k feldspar
secondary: kaolinite (phyllosilicate)
139
is plagioclase supply or kinetically limited?
supply
fast weathering > uplift
140
is K feldspar kinetic or supply limited?
kinetic
slow weathering rate
141
what does weathering rates increase with?
increasing surface area ie grain size decrease
142
what is the difference between soil and saprolite?
soil = highly disaggregated material, easily mobilised
saprolite = retains original rock structure, primary minerals replaced with secondary and increased porosity
143
what is enhanced weathering CDR technology?
Carbon Dioxide Removal by crushing up mafic silicate rocks and spreading them widely across land surfaces
144
what is primary production?
the synthesis of organic compounds from CO2 in the surrounding environment representing a store chemical energy
145
what is gross primary production?
the rate at which CO2 is transformed into organic carbon per unit area by an ecosystem gC/m2/day
146
what is autotrophic respiration?
the chemical energy stored in cellulose, sugars and starches being released to fuel plant metabolisms
147
what is net primary production?
NPP = Gross Primary Production -Autotrophic respiration
the net rate at which plant biomass is being produced
148
what are the controls on global net primary production?
water availability
photosynthetically active radiation (PAR)
temperature
149
what is assimilation?
growth of the consumer
150
how do heterotrophic organisms consume organic matter?
assimilation
respiration
excretion
151
what is net ecosystem exchange?
the net change in carbon storage in both the living and abiotic organic matter pools of the terrestrial biosphere.
NEE = NPP - heterotrophic respiration+fire
152
what are sources and sinks of CO2 in the terrestrial biosphere?
sinks : litterfall + photosynthesis
sources : autotrophic respiration + heterotrophic respiration + fire
153
what are some soil organic matter decomposers?
fungi
bacteria
protozoa
earthworms
nematodes
arthropods
154
where are the highest concentrations of soil organic matter?
northern latitudes - tundra and boreal forest biomes
permafrost
155
how much carbon is stored in permafrost?
1300 Gt C
x2 amount in atmosphere
156
why is so much carbon stored in permafrost?
seasonal liquid water allowing plant growth (active layer) overlying permanent frozen soil that prevents respiration of soil organic matter (syngenetic permafrost growth)
157
what is cryoturbation?
the expansion and contraction of soil volume through freeze-thaw cycles that causes turbulent mixing of soil layers
158
does net primary production increase or decrease with increasing atmospheric CO2?
increases
159
what can limit biomass growth on a local scale?
nutrient availability
160
What is Liebigs law of the minimum?
growth of biological populations is limited by the scarcest resource
161
what are the macro nutrients?
CHONPS
make up 98% of biomass
162
what are the most common limiting nutrients?
N and P
lowest environmental availability relative to biological demand
163
what are the nutrient sources to the critical zone?
atmosphere - fixation of atmospheric gases, deposition of aerosols
geosphere - uplift of rocks releases nutrients by chemical weathering
164
how are nutrients lost from the critical zone?
soil erosion
leaching
harvesting of biomass
165
why is Phosphorus required in living organisms?
phosphate ester bridges bind helix strands of DNA and RNA
166
What are the inputs of phosphorus in the critical zone?
chemical weathering of igneous rocks ie apatite, sedimentary rocks ie authigenic carbonate fluorapatite
no gaseous form
167
why is Nitrogen required in living organisms?
NH2 amino groups
168
what forms of nitrogen are available for use by most organisms?
nitrate NO-3
ammonium NH+4
169
what are the main reservoirs of nitrogen on earth?
50% inert N2 gas
minimal in crust
170
what are the sources of nitrogen into the critical zone?
nitrogen fixation by cyanobacteria and fungi
N2 +16ATP = 2C-NH2
171
what is nitrification?
the fixation of ammonia to nitrate
occurs in oxygenated soil pore spaces
driver of soil acidification
172
what is denitrification?
conversion of nitrate to inert N2 gas
occurs in anoxic soil pore spaces
173
what is the typical nutrient cycling of a natural ecosystem?
efficient recycling between living biomass and soil nutrient stores
minimal external loses
sustainable nutrient stores
174
what is the typical nutrient cycling of agroecosystems?
accelerated external nutrient losses
Unsustainable
nutrient stores decline over time
requires input from fertilizers
175
what are natural fertilizer?
nutrients derived from existing biomass
local biomass into soil ie manure and compost
new nutrients from external areas ie guana and bone meal
176
what are synthetic fertilisers?
nutrients derived from atmosphere and rocks
Haber-Bosch process
N2 + 3H2 -> 2NH3
177
What are the consequences of doubling N and P supply to the critical zone?
eutrophication - algal blooms, low oxygen
178
how do soils form?
through pedogeneisis
179
what is translocation?
processes that result in the internal redistribution of soil components from shallower to deeper layer
180
what is eluviation?
drainage of water through the soil profile resulting in the leaching of organic matter and secondary minerals from upper soil layers
181
what is illuviation?
the accumulation of leached organic matter and secondary minerals in deeper sections of the soil profile plane
182
what are the soil horizons (epipedons)?
O - Organic matter from plant and animal detritus
A - A mixture of minerals and humified organic matter. highly weathered mineral Assemblages
E - Eluviation top layer. Al Fe oxides/oxyhydroxides and/or organic matter. courser mineral phases (quartz)
B - Bottom of layer, accumulation of material by illuviation
C - unConsolidated material overlying saprolite (parent material). outside influence of biological cycle, low chemical weathering
183
what are the six classifications of soil taxonomy?
in order of increasing specify:
order - presence or absence of a diagnostic horizon
suborder - based on moisture and/or temperature regime
great group
subgroup
family
series
184
what are the 12 soil orders in the USDA classification?
entisol
enceptisol
gelisol
histosol
andisol
vertisol
aridisol
mollisol
spodosol
alfisol
ultisol
oxisol
185
what are the factors that control soil formation?
Climate - chemical/physical weathering regime. biomes. soil moisture regime.
Organisms - production and cycling of soil organic matter
Relief - controls uplift/erosion rates
Parent Material - primary mineral composition
Time - extent of transformation
(PORT C)
186
what are entisols and inceptisols and where are they found?
poorly developed soils - lack of time or arid climate.
Arid, mountainous regions, recently deposit fluvial sediments
entisol11% land - no soil formation, no soil horizons
inceptisols 16% land - weak development of horizons
187
what are the moderately developed soils and their characteristics?
aridsols 23% land - arid deserts, too dry for plants, diagnostic ochric epipedon horizon
mollisols 4% land - dry temperate grasslands, mollic horizon rich in SOM, agriculturally productive, mid latitudes
alifsols 13% land - humid deciduous forest, diagnostic illuviation subsurface horizon with phyllosilicate, mid latitudes
spodosols 5% land - wet & cool coniferous forests. E horizon that has been extensively leached, to a quartz rich layer above diagnostic B horizon with SOM
188
what are strongly developed soils and their characteristics?
warm and wet climates of tropics and sub tropics = high weathering
ultisols 9% land - high quartz, kaolinite, Fe oxides/oxyhydroxides, translocation of clay minerals forming B horizon
oxisols 8% land - quartz, kaolinite, Fe oxides/ocyhydroxides. lack distinct horizon development
189
what soils are controlled by temperature/water regime?
important stores of soil organic carbon
polar and alpine tundra
gelisols 6% land - permafrost, high SOM, high physical weathering due to freeze thaw (cryoturbation)
histosols 1% land - >25% SOM, waterlogged environments (peat, bogs) prevents respiration
190
what are soils with specific minerals that dictate their properties?
andisols <2% land - volcanic ash, young, rich in amorphous secondary minerals (allophane, imogolite, ferrihydrite), high water holding capacity, high agricultural productivity
vertisols 2% land - >30% smectites, network of vertical cracks, form from the weathering of limestones and mafic rocks, tropics.
191
what is land degradation?
negative trend in land condition caused by (in)direct human induced processes (ie climate change) expressed as a long term reduction/loss of biological productivity, ecological integrity, and/or value to humans
192
what is desertification?
land degradation in arid, semi arid and dry sub humid regions from human activities and climatic variations
193
what is a biome?
ecosystems that share the same broad structure
194
how much of earths land surface has been altered by humans?
75%
195
what are some of the main underlying causes for land degradation?
soil compaction/sealing
soil nutrient depletion
SOM depletion
soil salinization
soil acidification
soil pollution
accelerated soil erosion
196
to what degree is agricultural soil erosion rate increased compared to natural systems?
10-100s times higher
197
what is a T value?
maximum average annual soil loss by erosion that will allow maintained agricultural production levels
0.4-1 mm/yr
198
what is the mean soil production rate?
0.036 mm/yr
199
what are the impacts of accelerated soil erosion on agriculture?
loss of secondary minerals and SOM due to finer grain sizes - affects stores of soil nutrients and water
Major loss of nutrients
200
what are the mechanisms of soil erosion?
detachment
transport
deposition
201
what are the agents of soil erosion>
entrainment of soil particles in flows of WIND, WATER and ICE
202
what is water erosion?
the splash effect
impact of raindrops = detachment of soil particles and their local lateral displacement
plant cover reduces this
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when does surface run off occur?
when soil pores are completely water saturated
precipitation rates exceed infiltration rates into dry soils
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what are the types of water erosion?
sheet erosion - soil is removed in a uniform layer
rill erosion - soil is removed from irregularly dispersed channels
gully erosion - soil is removed from along a concentrated flow path
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what is the universal soil loss equation (USLE)?
Calculates mean annual soil loss by sheet and rill erosion
Annual average soil loss = Rainfall erodibility factor x K soil erodibility factor x sLope length factor x Slope steepness factor x Cover management factor x supporting Practices factor
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what is K, the soil erodibility factor?
resistance to detachment
runoff vs infiltration of rainfall
sand and clay , low K
Loams high K (0.25-0.5)
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What does S and L, slope steepness and slope length mean?
topography
controls the energy of flows of surface runoff
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what is C, the cover management factor?
the extent to which the soil is covered by plants and plant residue, protecting soil from erosive energy of rainfall
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what is P, supporting practices factor?
engineering and agricultural practices that help minimize soil erosion
ie terraces and contour tillage
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what is the downstream impacts of erosion?
deposition in floodplains
Dams disrupt transfer of sediment, deposition in reservoirs, reduces the delivery of nutrient stores to downstream ecosystems/agricultural areas
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how much carbon is released due to extraction from mining?
153 Gt/yr
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