LEC.103 Environmental Processes & Systems Flashcards
1
Q
What are the 3 erosional landforms that provide evidence for glaciation?
A
- Glacial cirques/corries
- Crag-and-tails
- U-shaped valleys
2
Q
How do glacial cirques form and how can they be used in climate reconstruction?
A
Hollows sheltered from heat so accumulation of snow/ice –> glaciers, ancient snowlines can be compared with present day snowlines to calculate temp. changes
3
Q
How do crag-and-tails form?
A
Resistant block of rock protects weaker rock in its lee from glacial erosion
4
Q
What are drumlins (depositional landforms)?
A
Oval mounds of glacial till that elongate parallel to ice flow
5
Q
What are eskers (depositional landforms)?
A
Sinuous ridges of glacial-deposited material
6
Q
What are tuyas and how can they be used in climate reconstruction?
A
Flat-topped volcanoes formed by a volcanic eruption beneath a glacier, shows that must have formed in cold climate + indicates thickness of ice at time of eruption using altitude where subglacial features become subaerial
7
Q
How can fossil sand dunes be used in climate reconstruction?
A
Found in areas of high rainfall so indicate increased rainfall since dune formation
8
Q
What 3 types of fossils can be used in climate reconstruction?
A
- Macrofossils (body/vegetation/trace)
- Pollen (microfossils)
- Diatoms (microfossils)
9
Q
How can palynology (study of pollen) be used in climate reconstruction?
A
Sediment may contain pollen grains from vegetation so analysis of abundance/type of pollen grains shows vegetation at time of deposition
10
Q
What are diatoms and how can they be used in climate reconstruction?
A
Aquatic microscopic algae that are sensitive to different environmental conditions, variations in species abundance provides picture of water quality
11
Q
What are 3 types of diagnostic rock and where are they found?
A
- Till (glacial)
- Coral reef (tropical sea)
- Scree (frosty hillside)
12
Q
What kind of sediment do glaciers and rivers deposit?
A
Glaciers: Poorly-sorted, angular sediment
Rivers: Well-sorted, rounded sediment
13
Q
What are varves?
A
Regular alternations in glacial LAKE sediment layers (pairs represent annual seasonal deposition), 1 varve = 1 dark + 1 light layer
14
Q
Why are varves not prevalent in saltwater settings?
A
The clays coagulate
15
Q
What kinds of sediment do the different layers in varves have?
A
Thicker, light layers: Coarse-grained, silt (spring/summer = more meltwater)
Thinner, dark layers: Fine-grained, clay (autumn/winter)
16
Q
What does the thickness of a layer in a varve show?
A
How much meltwater is present
17
Q
What are 2 types of non-diagnostic sediment?
A
- Sand
- Mud
18
Q
What are the 3 types of modern sand and what do they all have?
A
- Fluvial
- Marine
- Desert
All have ripples with cross-laminations due to grain transport by air/water
19
Q
What are the differences between desert and fluvial cross-beds?
A
Desert: Larger, different orientations
Fluvial: Smaller, often unidirectional
20
Q
What 4 sedimentary structures allow interpretation of the environment of deposition?
A
- Cross-beds
- Flute marks
- Desiccation cracks
- Rain pits
21
Q
What is used to distinguish between fluvial, marine, and desert sand?
A
Textural and compositional maturity of sand, fossils, rock colour, and calcrete
22
Q
How does textural maturity allow desert and fluvial sand to be distinguished?
A
Rounded grains = desert
Angular grains = fluvial (less angular the longer transported for)
23
Q
How does compositional maturity allow marine and fluvial sand to be distinguished?
A
More resistant particles = marine (more erosion so less resistant particles already broken down)
Less resistant particles = fluvial
24
Q
How can calcrete be used to diagnose sediment?
A
Calcrete is fossil soil so presence of calcrete shows sediment was on land in a semi-arid environment
25
What are 3 challenges in reconstructing past climates?
1. Incomplete record due to erosion
2. Sea floors offer continuous stratigraphic record but sea floor destroyed by subduction
3. Fossil records less easy to interpret the further back in time you go (evolution/extinction)
26
What is the evidence for a potential 'Snowball Earth' during 700-650 Ma (Precambrian)?
Glacial deposits found on all continents
27
What might have the 600 Ma old (Precambrian) glacial deposits found in the UK been caused by?
Glaciation may have been related to tectonic movement/continent disruption
28
What happened during the Ordovician Ice Age (440 Ma)?
Large mass of continents (Gondwanaland), Sahara at S Pole where bedrock was scratched by glaciers, no glacial deposits in UK but coral reefs deposited so UK at 25°S
29
What happened during the Permo-carboniferous Ice Age (290 Ma)?
Large continental mass over S Pole again, no glacial deposits in UK but tropical rainforest growth --> coal accumulations so UK at equator
30
What happened during the Cenozoic Ice Age (30 Ma - present)?
Polar ice sheets grew, sea level fell, alternations of glacial and inter-glacial periods
31
What causes the alternations between glacial and inter-glacial periods?
Astronomical cycles - glacial/inter-glacial periods correspond to variations in the heat Earth receives from the Sun (results from sum of all of Earth's orbital changes)
32
What was the last inter-glacial period called and what type of fauna lived in the UK during this time?
Ipswichian, tropical (hippo/tortoise skeletons found near London)
33
What was the last glacial period called, how much lower was global sea level, and what did the cooling climate lead to?
Devensian, ~150m lower, deforestation (pollen records)
34
What is the name of the current inter-glacial period we are living in?
Holocene
35
How are deep sea cores used in climate reconstruction?
Coarse debris indicates iceberg rafting, foraminifera indicate water temp. and ice vol. (study changes in species frequency)
36
What are foraminifera and what does a high ratio of them mean?
Microscopic aquatic organisms with CaCO3 shell + sensitive to water temp./salinity, high ratio = warm water (inter-glacial)
37
How is measuring 18O/16O ratios in calcitic tests used in climate reconstruction?
Light isotope evaporates so...
Glacial = 16O stored in ice and ocean enriched in 18O
Inter-glacial = 16O evaporates but returns via rivers to oceans so ratio unchanged
38
What are the 2 forms of relative dating used to date rocks and what is a challenge to relative dating?
1. Stratigraphy (rock layers)
2. Fossils
Challenge: Folding
39
How do fossils allow us to date rocks (relative dating)?
Trilobites = older, Paleozoic
Corals = younger, Mesozoic
40
What is the technique used in absolute dating of rocks?
Isotopic/radiometric dating
41
Which isotopes are used in radiometric dating?
Unstable isotopes that radioactively decay
42
What happens during radioactive decay of an unstable isotope's nucleus?
An electron is emitted, producing a proton and forming a daughter element
43
What is half life in terms of radioactively decaying isotopes?
Time for 1/2 of original number of radioactive atoms to decay
44
What are examples of an isotope with a long half life and a short half life?
Long: 238U (used for old minerals)
Short: 14C (used for young material)
45
Explain 14C dating
Living organisms incorporate C into their tissues, after death C is no longer absorbed so 14C in tissues decays --> amount of 14C left in fossil measured to determine time of death
46
Why is radioactive decay used as a clock?
1. Half life of radioactive atoms is known for radioactive isotopes
2. Half life doesn't vary with changes in T or P
3. Can measure ratio of parent:daughter atoms in rock sample
47
What are the complications with isotopic/radiometric dating?
1. Partial resettling
2. Some of daughter element may already be present at start
48
Explain partial resettling
If a rock is reheated above its closure temp., the clock resets - if it only just reaches this temp., clock partially resets
49
What 2 things have been established from relative and absolute dating techniques?
1. Age of the Earth
2. Earth has been shown to have been repeatedly shaped by environmental processes/systems
50
What are the 3 ways ice cores record paleao-environments?
1. Changes in ppt. rate over time
2. Past atmospheric composition (trapped air bubbles of CO2/CH4)
3. Melt layers (no bubbles) - relates to summer temps.
51
How are ice cores dated?
1. Annual variations in snow properties (dark bands in winter when snow mixed with dust, light bands in summer when more ppt.)
2. Radiometric dating of dust/volcanic ash layers (when banding is less visible at depth)
52
Which forms of ice are meteoric ice?
Ice sheets and valley glaciers
53
How is an ice shelf formed?
Snow compresses to form ice --> ice builds up + flows outwards --> ice sheet --> ice shelf
54
What does the equilibrium line show?
Above = net gain in ice, below = net loss of ice
55
Which Antarctic ice sheet is less stable (more net loss)?
West Antarctic ice sheet
56
Which Arctic ice sheet holds enough ice to raise the global sea level by 7m?
Greenland ice sheet
57
What is the difference between ice sheets and ice caps?
Ice sheets = >50,000 km2
Ice caps = <50,000 km2
58
What are ice divides?
Ice dispersal centres/ridges/domes
59
What are outlet glaciers/ice streams?
Fast-flowing and responsible for majority of ice discharge
60
What are ice shelves?
Floating extensions of ice sheets
61
What are 4 reasons why the cryosphere is important?
1. Water resource
2. Tourism
3. Earth's energy balance
4. Sea level
62
What % of solar radiation does snow reflect compared to water?
80%, water is 6%
63
What is the ice albedo positive feedback loop?
Atmos. warms --> ice melts, decreasing Earth's albedo --> more solar radiation absorbed at surface
64
What does astronomical theory show about quaternary climate change?
It was global scale, multiple events, cyclical, and high magnitude
65
What does Maunder minimum mean?
Fluctuations in iceberg-rafted debris and carbon-14 suggests varying sun can cause millenial climate change
66
What are the 3 changes to Earth's orbit that James Groll proposed ice ages result from?
1. Eccentricity (circular/elliptical pathway around Sun)
2. Obliquity (orientation/tilt)
3. Precession ("wobble", affects perihelion/aphelion)
67
When do glaciations occur in terms of the Earth's orbit?
Greatest eccentricity and minimum obliquity
68
What are challenges to using Milankovitch cycles to explain ice ages?
1. 100,000 year cycle
2. Changes in insolation are too small to explain large changes
3. Milankovitch cycles are symmetrical but ice age cycles aren't
69
How much more dust was there in the atmosphere during the LGM (last glacial maximum) than today and what does this dust do?
20x more, reflects radiation
70
How much less CO2 is there in glacial conditions as a %?
50%
71
Explain the African humid period and why was it important?
Groundwater formation, monsoon brought more rainfall north, 'Green Sahara' during early Holocene, important for modern water supply
72
What is the evidence for increased precipitation after the LGM?
Lake Mega-Chad was 150% deeper than today (evidenced by fossil shorelines)
73
What were the potential 2 causes of mass extinction at the end of the LGM?
1. Climate change
2. Humans
74
What is strongly linked to European climate?
North Atlantic Oscillation (NAO)
75
What does a positive and negative NAO mean for Europe's climate and which period does this link to?
Positive (direct route): mild/stormy/wet winters
Negative (meanders): cold/calm/dry winters
Medieval warm period
76
What is the evidence for the Little Ice Age (LIA) potentially being a global event?
Glacier fluctuations, ocean cores in Florida/Venezuela, ice cores in Andes/Peru, glacial maxima in Peru determined by terminal moraine
77
What were the impacts of the LIA?
Frost fairs on River Thames, crop failure, Viking settlements in Greenland abandoned
78
What were the 2 causes of the LIA?
1. Maunder minimum (virtually no sun-spot activity so maximum cooling)
2. 1815 Tambora eruption ('year without summer')
79
What is the most important factor in 20th century warming and which year is currently the warmest year on record?
Greenhouse gases, 2016
80
Why are the tropics warmer than the poles?
Same amount of radiation has to cover a larger surface area near poles so energy deficit at poles
81
How do the tropics not overheat?
Redistribution of energy via poleward heat transport
82
What are the 3 ways poleward heat transport occurs so that the tropics don't overheat?
1. Oceanic flux
2. Atmospheric sensible heat flux (conduction)
3. Atmospheric latent heat flux
83
What are the 2 types of general circulation?
1. Primary (large scale, all times)
2. Secondary (day-to-day weather)
84
What are 2 features of low pressure systems?
1. Cyclonic circulation (same direction as Earth's rotation)
2. Rising air
85
What are 2 features of high pressure systems?
1. Anti-cyclonic circulation (opposite direction to Earth's rotation)
2. Descending air
86
Describe Coriolis force
Earth rotates ~15°/hour so air is deflected right in N. hemisphere and left in S. hemisphere
87
Why is the Coriolis force strongest at the poles and zero at the equator?
Speed of Earth's rotation changes across latitudes
88
What are the 4 semi-permanent pressure systems that the 3 cell model and Coriolis force combine to produce?
1. ITCZ (Intertropical Convergence Zone) equatorial low
2. Subtropical highs
3. Subpolar lows
4. Polar high
89
What are Rossby waves driven by and what is this a measure of?
Potential vorticity, measure of how much air is rotating
90
In what direction will air pushed N and S travel in, why, and what is this called (Rossby waves)?
Clockwise, compensates for Earth's anti-clockwise rotation, anticyclonic swirl
91
At what latitude does air have cyclonic swirl (Rossby waves)?
0°
92
What creates the wave motion in Rossby waves and where do Rossby waves occur?
Air particles oscillating N and S, along boundaries of warm and cool air (Polar-Ferrel boundary)
93
What are jet streams?
Very fast windfields embedded in Rossby waves between high and low pressure systems
94
How are jet streams formed?
Air is pushed from high to low pressure by pressure gradient force (PGF) and is deflected right by Coriolis force in N. hemisphere --> eventually PGF and Coriolis force balance out --> steady flow of geostrophic wind
95
What are the 2 jet streams that both the N. and S. hemisphere have?
1. Polar jet
2. Subtropical jet
96
What are the 5 roles of the ocean?
1. Absorbs + stores solar radiation
2. Distributes heat around globe + regulates global climate
3. Integral to water cycle
4. Absorbs atmospheric CO2
5. Produces atmospheric O2
97
How does the the ocean store and absorb solar radiation?
High heat capacity, especially at equator and 70% of Earth's surface
98
How does the ocean distribute heat around the globe and regulate global climate?
Ocean currents carry warm water poleward and cold water equatorward (counteracts uneven distribution of solar radiation + drives weather patterns)
99
How is the ocean integral to the water cycle?
Ocean evaporation - almost all rain on land from oceans (tropics particularly rainy)
100
How does the ocean absorb atmospheric CO2?
Largest carbon sink (can lead to ocean acidification as CO2 and H2O make H2CO3)
101
How does the ocean produce atmospheric O2?
Ocean phytoplankton + plants produce 70% of world's atmospheric O2 via photosynthesis
102
What are the 3 physical properties of the ocean, what is the same for each, and what are each of their 'clines' called?
1. Salinity - halocline (sharp change)
2. Temperature - thermocline
3. Density - pycnocline
Surface ocean variable (latitude), deep ocean uniform (formed in polar regions)
103
What does ocean density drive and which type of water is denser?
Ocean dynamics, colder + saltier water more dense
104
Why are gyres not a regular shape?
Coriolis effect offsets the centre of the geostrophic 'hill' west
105
What is an example of a gyre?
In Sargasso Sea:
Western boundary: Gulf Stream (deeper/warmer/narrower/stronger currents)
Eastern boundary: Canary Current (shallower/colder/wider/slower currents)
106
What is Meridonial Overturning Circulation (MOC)?
Total circulation in latitude-depth plane
107
What is southern oscillation?
Slow see-saw in pressure across equatorial Pacific
108
What is Southern Oscillation Index?
Pressure difference between Tahiti and Darwin
109
What is NAO?
Slow see-saw in pressure across North Atlantic
110
What is NAO Index?
Pressure difference between Icelandic low and Azores high
111
Define climate and what are its 3 main components?
Long-term, general state of atmosphere
1. Precipitation
2. Thermal conditions
3. Seasonal variation
112
Which direction does the ITCZ move during summer?
North
113
What do the letters mean in Koppen-Geiger climate classification (A, B, C, D, E, Af, Am, Aw/As)?
A = tropical
B = dry
C = temperate
D = continental
E = polar
Af = tropical rainforest (no dry season/seasonality)
Am = tropical monsoon (wet + dry seasons, not hot + and cold)
Aw/As = tropical wet, tropical dry/savanna
114
What is monsoonal circulation and what 3 things is it exacerbated by?
High-low pressure circulation
1. Cross-equator season change (winter in S., summer in N.)
2. Land-ocean boundary parallel to equator
3. Orography
115
What is sensible heat (glaciers)?
Air warmer/cooler than ice
116
What is the ablation area of a glacier?
Net loss of ice
117
Describe "warm", "cold", and polythermal ice
"Warm": At pressure melting point, contains water, faster, more erosive
"Cold": Below pressure melting point, all frozen, slower, less erosive, near poles
Polythermal: Both "warm" and "cold" ice
118
What are the 4 dynamics of glaciers?
1. Rigid bed + "warm" ice: basal sliding, little creep, fast-moving
2. Rigid bed + "cold" ice: negligible sliding, creep only, very slow-moving
3. Soft bed + "warm" ice: sub-glacial sediment deforms, some sliding, little creep, fast-moving
4. Soft bed + "cold" ice: some sediment deformation/sliding, little creep, slow-moving
119
What is creep related to (glaciers)?
Shear stress (i.e. ice thickness, slope angle)
120
What can result from extreme glacial erosion?
Meltwater flood
121
What are 6 features produced by glacial erosion (macroscale)?
1. Hanging valley
2. U-shaped valley
3. Cirques
4. Spurs
5. Truncated spurs
6. Arete
122
What are 3 features produced by glacial erosion (meso- to microscale)?
1. Drumlins
2. Striations
3. Roche moutonnees
123
What can glacial deposits either be and which sediments are deposited by ice and meltwater?
Subglacial or supraglacial debris
Deposited by ice: till, moraine, glaciofluvial sediments
Deposited by meltwater: silts/clays, moraine, glaciofluvial sediments
124
What are the 4 types of till deposited by glacial ice?
1. Ablation
2. Melt-out
3. Flow
4. Lodgement
125
What are 3 processes that form moraine?
1. Push moraine
2. Dump moraine (debris slumps)
3. Ablation moraine (clean ice melts between supraglacial debris along englacial debris bands --> forms ice core + ablation moraine)
126
What are 5 types of weathering?
1. Thermal expansion
2. Unloading (uplift + weathering so less pressure so cracks)
3. Salt crystallisation
4. Biological
5. Clay hydration (water stored between molecular sheets expands + breaks clay)
127
In what conditions is there stronger chemical weathering?
High temperature and precipitation (opposite for strong mechanical weathering)
128
What are 3 examples of mass movement processes in drylands?
1. Aeolian mass movement (wind moving particles e.g. long term suspension)
2. Gravitational instability
3. Flash floods
129
How does a sand dune form?
Decreased wind velocity at lip crest so saltating grains deposited --> oversteepened lip destabilises --> slip on slip face --> slip face moves forward to preserve progression
130
What are the 3 types of sediment?
1. Siliciclastic
2. Chemical
3. Biological
131
Which siliciclastic minerals are low, medium, and high weathering?
Low: quartz, feldspar, mica, pyroxene, amphibole
Medium: quartz, feldspar, mica, clay minerals
High: quartz, clay minerals
132
Where is sediment stored?
Continental and oceanic sedimentary basins (active/passive margins in oceanic)
133
What 2 things control erosion rate and therefore sediment discharge into oceans?
1. Topography
2. Precipitation
134
What are 2 reasons why sedimentary basins are important?
1. Groundwater aquifers form in sedimentary basins
2. Mineral resources + waste disposal
135
What are the 3 ways accommodation space can be created for sediments?
1. Tectonic subsidence
2. Sea level change
3. Isostasy
136
Describe the 3 steps of tectonic subsidence (creating accomm. space for sediments)
1. Contraction of cooling lithosphere (thermal relaxation)
2. Crustal extension
3. Crustal loading
137
Describe crustal extension (step 2 of tectonic subsidence)
Mantle plume rises and lifts crust upwards (upwarping) which pushes crust apart --> rifting --> forms new ocean and MOR if continues
138
Describe the 4 steps of crustal loading (step 3 of tectonic subsidence)
1. Sediment input loads crust
2. Accommodation space filled
3. Shoreline moves forward
4. More accommodation space opens
139
What are the 2 sets of laws used in fluid mechanics?
1. Newton's 3 laws of motion
2. Laws of conservation (mass, momentum, energy)
140
What is the difference between when a fluid is incompressible compared to compressible?
Incompressible: Same amount that goes in must come out
Compressible: Difference in change in flow speed across box is the rate at which density in the box is changing
141
What does increased viscosity mean?
Increased thickness
142
What is the difference between stress and pressure?
Stress: Parallel or perpendicular to the surface
Pressure: Perpendicular to surface only
143
Does steadiness increase or decrease from laminar flow --> transition flow --> turbulent flow?
Decreases
144
What number is used to predict which flow type occurs (laminar/transition/turbulent)?
Reynolds number (laminar = lower number)
145
Is pahoehoe or a'a lava flow more viscous (thick)?
A'a lava flow
146
What does turbulence make fluid flows more effective at?
Moving/spreading/dispersing material
147
Does number of particles in a flow increase/decrease with these particle-dominated flows: hyper concentrated flows --> mud flows --> debris flows --> rockfall?
Increases
148
What are the 4 causes of debris flows?
1. Addition of moisture (adds weight + lubrication)
2. Removal of support (stream erosion at base of valley walls)
3. Deforestation/wildfires (loss of support + accumulation of moisture)
4. Volcanic eruptions (melt snow/ice)
149
What is rheology the study of?
The study of flow of matter
150
What is soil formed by and what kind of source is it?
Weathering of rocks, almost non-renewable source
151
What are the 6 functions of soil?
1. Food/fibre production
2. Environmental interaction
3. Support of ecological habitat + biodiversity
4. Protection of cultural heritage (vital part of landscape)
5. Providing platform for construction
6. Providing raw materials
152
What are the 5 main threats to soil function?
1. Erosion
2. Compaction
3. Contamination (e.g. Pb)
4. Organic matter (loss = loss of fertility, increased erosion risk, + less water holding capacity)
5. Salinisation
153
How was soil first ever produced?
Fine silicate dust produced by volcanic/impact events + altered by water/air/life
154
What are the 5 factors controlling soil formation?
1. Parent material
2. Climate
3. Biota
4. Topography
5. Time
155
What are 2 examples of parent materials in soil formation?
1. Residual materials
2. Organic deposits (mainly in cool climates that have been glaciated)
156
How can ppt. and temp. (climate) affect soil formation (3 ways)?
1. Affect physical/chemical weathering + biological processes
2. Carbonates can accumulate at shallow depths when low ppt.
3. Acidic soils form in humid areas
157
How can biota affect soil formation?
Micro-organisms decompose organic matter + form weak acids which helps soil formation
158
How can topography affect soil formation?
Soils on steep hillsides have thin horizons so better drained so more wind/water erosion
159
What is a layer of soil called?
Horizon
160
What are the 5 processes during soil formation?
1. Addition
2. Removal
3. Mixing
4. Translocation
5. Transformation
161
What are the 2 components of soil?
1. Pore space (air/water, dependant on climate, smaller pore size = better for water)
2. Soil solids (mineral/organic)
162
What are 5 functions of organic matter?
1. Supply nutrients
2. Maintain structure
3. Store water
4. Absorb heat (dark colour)
5. Deactivate chemicals (bind herbicides)
163
What are the 6 physical properties of soil?
1. Colour
2. Texture
3. Density
4. Aggregates
5. Pore space
6. Structure of of mineral soils
164
What are the 3 factors affecting soil colour?
1. Carbon (dark brown-black organic matter)
2. Water (darkens soils)
3. Chemical (well-drained soils with more O2 are red due to highly oxidised Fe2+)
165
Define gleying
Fe in a reduced state which gives grey/blue/green colour (indicative of waterlogged conditions - low O2)
166
What are the 3 types of soil structure?
1. Granular
2. Blocky
3. Platy
167
What 3 things does soil structure affect?
1. Air/water movement
2. Biological activity
3. Root growth + seed emergence
168
What are 5 key reactions/processes in soil?
1. Ion exchange + adsorption/desorption
2. Cation/anion exchange
3. Ppt. + dissolution
4. Complexation
5. Oxidation/reduction
169
What are 3 examples of microcontaminants in soil?
Pb, Cd, As
170
What does soil pH influence?
Solubility/variability of plant nutrients/pollutants, particularly metals
171
What is cation/anion exchange capacity?
Propensity for adsorbing cations/anions
172
What does the sorptive property arise from?
Electrical charges and the large surface area of clay minerals + humus
173
How do soils act as a buffer zone between the atmosphere and groundwater?
Contain clay minerals and organic matter which adsorb ions/molecules/gases
174
When is the affinity of an adsorping surface to cations greater?
1. Greater affinity for divalent ions than monovalent
2. Greater affinity for larger cations than smaller ones of same charge because larger = less hydrated
175
Define active and reserve acidity
Active = due to H+ activity in soil solution
Reserve = represented by H+ that are easily exchanged by other cations
176
What are 2 ways of neutralising soil acidity?
1. Liming with limestone (replaces H+/Al3+ with Ca2+)
2. Adding gypsum/organic matter (reduces Al3+ toxicity)
177
What are 5 functions of humus?
1. Holds water/nutrients
2. Sticks together + helps to establish/maintain strong crumb structure (so less soil erosion)
3. Provides some nutrients as slowly decayed by microbial activity
4. Buffers effects of pesticides
5. Creates good soil "tilth"
178
What are the 6 types of forest?
1. Tropical rainforest
2. Subtropical forest (moderate diff. between summer/winter)
3. Tropical seasonal (monsoon) forest
4. Temperate rainforest (colder, seasonality in both temp. and ppt.)
5. Temperate deciduous forest (marked temp. seasonality, tree canopy dominated by 2-3 species)
6. Boreal conifer forest (strongly seasonal climate - long winters/short summers)
179
Describe tropical and temperate grasslands
Intermediate between forest and grassland, precipitation is non-uniform, fire and grazing are widespread
180
Describe Mediterranean woodlands
Warm, dry summers + cold, moist winters, fire = important factor so plants are adapted for quick regeneration
181
Describe deserts
Dry, hot = subtropical, cold = arctic, xerophytes store water + reduce evapotranspiration, phreatophytes grow very long roots
182
Describe tundra
Very cold so water permanently frozen in subsoils (permafrost), plants have shallow roots to avoid permafrost, waxy leaves to preserve water, trichomes (hair on flowers/stems) to trap heat, + dry out + regrow when enough moisture is present
183
What is Liebig's Law of the Minimum?
Most limiting factor controls the response of an individual
184
Define niche
A multi-dimensional description of a species' resource needs, habitat requirements, and environmental tolerances
185
What does a realised niche require?
Overlap of biotic, abiotic, and movement processes
186
When is there a likely establishment of an invading species but a low invader response?
If there is an overlap but the invading species specialises in the same niche as the original community
187
What are the 3 types of change in an ecosystem?
1. Regeneration change (results from natural processes of germination, cyclic)
2. Fluctuation change (biomass varies from a mean state of longer/shorter periods of time, reversible)
3. Successional change (change from one type of biomass/community to another, non-reversible)
188
Describe gap regeneration (6 steps)
1. Windthrow creates gap in biomass
2. Rapidly growing invasive species
3. More species colonise gap
4. Seedlings of dominant trees grow below invasives
5. Saplings of dominant tree species eventually overtop invasives
6. Fill gap + compete for resources
189
Describe a regeneration mosaic
Natural woodland contains patches that vary in composition depending on time since regeneration gap was created
190
What 2 things does fluctuational change result from?
1. Phenological changes associated with seasonal climatic regimes (warm/cold, wet/dry)
2. Short term environmental variation - effects depend on intensity/duration of deviation from mean conc., can change relative importance of component species in community
191
What is the difference between primary and secondary succession?
Primary = new surface
Secondary = recovery from vegetation removal
192
What are the 5 different types of succession?
1. Lithosere (plant succession that begins on newly exposed rock surface)
2. Psammosere (begins on sand)
3. Allogenic (driven by plants)
4. Degradative
5. Clementsian
193
Define biomass
Standing reserve of living organisms, expressed as energy/matter
194
Define NPP (Net Primary Productivity)
Gross primary productivity when energy is lost via plant respiration
195
How much more NPP happens in the terrestrial than the marine biosphere?
2x more
196
What are 5 limiting factors of NPP?
1. Water availability
2. Growing season length
3. Photosynthesis not 100% efficient
4. Shortage of minerals e.g. N
5. Temperature can benefit but interacts with water availability
197
What are autotrophs and heterotrophs?
Autotrophs = primary producers
Heterotrophs = consumers (herbivores = primary, carnivores = secondary, decomposers)
198
Define consumption efficiency, assimilation efficiency, and production efficiency
Consumption efficiency = proportion of total productivity at one level that is consumed by next
Assimilation efficiency = % of food energy that is retained + not lost as faeces
Production efficiency = rate at which assimilated energy is converted into new biomass
199
What 3 things increase the release and fixation of nitrogen?
1. Fossil fuels
2. Land clearing
3. Drainage of wetlands
