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Lund University, Deparment of Physical Geography and Ecosystem Science
Soils and weathering NGEA01, 2015
Cecilia Akselsson
Department of Physical Geography and Ecosystem Science
Lund University
Lund University, Deparment of Physical Geography and Ecosystem Science
Minerals and rocks
Today and tomorrow…
Weathering of soils for sustainable forestry
Photo: Jonas Åkerman
Photo: Cecilia Akselsson
Photo: Cecilia Akselsson
Soils
Lund University, Deparment of Physical Geography and Ecosystem Science
Litterature
+ Handout (exercise)
The first part of the chapter “Preliminaries to Erosion: Weathering and Mass wasting” (the part about denudation and weathering)
Lund University, Deparment of Physical Geography and Ecosystem Science
From rocks to soils to elements (e.g. Ca, P, K): Weathering - one of the denudation processes
Weathering: Mechanical, chemical and biological breaking down of rocks
Mass wasting: Short- distance downslope movement of broken rock material
Erosion: Removal, transportation and deposition of frag- mented rock material over wider areas (wind/water/ice)
(From Hess, 2013)
Lund University, Deparment of Physical Geography and Ecosystem Science
Weathering and mass movements in “Fjällen” (the Swedish mountains)
(Photo: Cecilia Akselsson)
Lund University, Deparment of Physical Geography and Ecosystem Science
Joints – where the weathering begins
Weathering occurs where atmosphere and litosphere meet. Microscopic openings, joints, faults, lava vesicles and solution cavities cause weathering not only on the surface
(From Hess, 2013)
Lund University, Deparment of Physical Geography and Ecosystem Science
Different types of weathering
Mechanical weathering: Breaking of rock material without any chemical changes
Chemical weathering: Decomposition of rock or soils by the the chemical alteration of the material
Biological weathering, according to the book: E.g. Plant roots penetrating cracks, lichens drawing minerals from rock through ion exchange, burrowing by animals
Biological weathering, in my research community: The impact of vegetation and funghi on weathering of mineral soils, e.g. through altering the chemical conditions in the soils (closely connected to chemical weathering)
Lund University, Deparment of Physical Geography and Ecosystem Science
Mechanical weathering – frost wedging (frostsprängning)
Freezing of water in cracks leads to expansion. Continuously freezing and thawing causes frost wedging. Occurs in many scales. Most common in high latitudes and on high elevations.
(From Hess, 2013)
Lund University, Deparment of Physical Geography and Ecosystem Science
Mechanical weathering – salt wedging (saltsprängning)
Salt crystallize when water evaporates. Crystals grow with time. In areas with dry climate and along ocean coast lines.
(From Hess, 2013)
Lund University, Deparment of Physical Geography and Ecosystem Science
Mechanical weathering – temperature changes
-Fluctuation of temperature from day to night and summer to winter can lead to expansion and contraction.
-Weakens and eventually cracks the rock.
-Could also happen at forest fires.
Lund University, Deparment of Physical Geography and Ecosystem Science
Mechanical weathering – exfoliation
Theory: Removal of weight, unloading, causes cracks, curved layers peel off
(From Hess, 2013)
Lund University, Deparment of Physical Geography and Ecosystem Science
Chemical weathering - Important for tree nutrition (P and base cations:Ca, Mg, K) and recovery from acidification
Ca2+ NH4+
K+ H+
H+ H+
H+
Lund University, Deparment of Physical Geography and Ecosystem Science
Chemical weathering
Mechanical weathering creates surfaces for chemical weathering. Chemical weathering can lead to release of different ions, e.g. Ca, Mg, K and P. Different types of chemical weathering: -Hydrolysis (Reaction with H2O) -Carbonation (Reaction with CO2) -Strong acids (Reaction with H+) -Reaction with organic acids -Oxidation (Reaction with O2)
Lund University, Deparment of Physical Geography and Ecosystem Science
Oxidation
“Rusting”: 4Fe + 3O2 → 2Fe2O3
(Photo: Cecilia Akselsson)
Lund University, Deparment of Physical Geography and Ecosystem Science
Hydrolysis
Reaction with water, example olivine:
Mg2SiO4 + 4 H+ + 4 OH - ⇌ 2 Mg 2+ + 4 OH - + H4SiO4
Carbonation
Reaction with carbonic acid, example calcium carbonate:
CO2 + H 2O → H 2CO3
H 2CO3 + CaCO3 → Ca2+ 2HCO3-
Reaction with strong acids, example K-feldspar 3 KAlSi3O8 + 2H+ +12 H2O → KAl3Si3O10 (OH)2 + 6 H4SiO4 + 2 K+
Strong acids
Lund University, Deparment of Physical Geography and Ecosystem Science
Important factors affecting chemical weathering rates
Presence of weathering agents:
-Hydrogen ions (H+)
-Water (H2O)
-Organic acids
-Oxygen (O2)
-Carbon dioxide (CO2)
Lund University, Deparment of Physical Geography and Ecosystem Science
Important factors affecting chemical weathering rates
Hardness and composition of material
7. QUARTZ 6. FELDSPAR 3. CALCITE
Reduced weathering rates
Lund University, Deparment of Physical Geography and Ecosystem Science
Total surface area
Important factors affecting chemical weathering rates
(From Hess, 2013)
Lund University, Deparment of Physical Geography and Ecosystem Science
Climate (temperature and moisture)
Important factors affecting chemical weathering rates
(From Hess, 2013)
Lund University, Deparment of Physical Geography and Ecosystem Science
Quantifying weathering rates of base cations 1
Budget calculations
Leaching
?
(Picture by Giuliana Zanchi)
Lund University, Deparment of Physical Geography and Ecosystem Science
Quantifying weathering rates of base cations 2
“Historical weathering rates”:
-Chemistry measurements at different depths.
-Assumption: Zirconium (Zr) resistant to weathering.
-Ratio between Zr and other elements on different depth gives weathering rates since last ice age.
(Photo: Cecilia Akselsson)
Lund University, Deparment of Physical Geography and Ecosystem Science
Quantifying weathering rates of base cations 3
Biogeochemical modelling
Decomposition of
soil organic matter
Soil moisture
PercolationSoil moisture
Soil chemistry and
weathering
Decomposition of
soil organic matter
Litter production Tree growth &
other processes
Hydrology
Nutrient
uptakeNutrients &
Al contents
Evapotrans.Soil
moisture
ForSAFE
Ground vegetation
composition
Soil acidity
& nutrients contents
Shading
Soil moisture
Litter productionNutrient uptake
Water uptake
Mineralization
DOC production
Soil acidity, N content, Al content
VEG
Lund University, Deparment of Physical Geography and Ecosystem Science
Causal loop diagram showing important factors affecting weathering rates…
Quantifying weathering rates with biogeochemical modelling
BC= base cations (Ca, Mg, Na, K)
Lund University, Deparment of Physical Geography and Ecosystem Science
Mini exercise: Climate change will change temperatures and moisture. It may also lead to increased harvesting (for biofuels). How
will weathering be affected?
BC= base cations (Ca, Mg, Na, K)
Lund University, Deparment of Physical Geography and Ecosystem Science
Mini exercise: Climate change will change temperatures and moisture. It may also lead to increased harvesting (for biofuels). How
will weathering be affected?
Lund University, Deparment of Physical Geography and Ecosystem Science
The PROFILE model
Weathering rates of BC are calculated as the sum of reactions between minerals and: -H+ -water -CO2 -Organic ligands
Field rate = ∑ ∑ Rate • A • f(moisture) •g (T) i
reactions minerals
j i j i j i j
Lund University, Deparment of Physical Geography and Ecosystem Science
wildfires greenhouse gases, aerosols
cloud formation
runoff
drainage
groundwater
weathering
nutrient uptake
litter
shortwave radiation
longwave radiation
greenhouse effect temperature
evaporation
ecosystem services
hydrosphere
biosphere
atmosphere
lithosphere
air pollution CO2 emission
primary production decomposition
precipitation evapotranspiration
(Borrowed from B. Smith)
Soils – where the atmosphere, lithosphere, hydrosphere and biosphere meet
Lund University, Deparment of Physical Geography and Ecosystem Science
Litterature
The chapter “Soils”
Lund University, Deparment of Physical Geography and Ecosystem Science
Soils and soil processes – decisive for feeding the world Some examples from the book “Jord” by Håkan Wallander
Lund University, Deparment of Physical Geography and Ecosystem Science
Soils and soil processes – decisive for feeding the world Example 1: Natural fertilization of agricultural land around the Nile
Lund University, Deparment of Physical Geography and Ecosystem Science
Soils and soil processes – decisive for feeding the world Example 2: Pine plantations along the south coast of Skåne to prevent erosion and transport of sand to agricultural land
(Photo: Cecilia Akselsson)
Lund University, Deparment of Physical Geography and Ecosystem Science
Soils and soil processes – decisive for feeding the world Example 3: Terraces on the slopes in Nepal to prevent landslides
(Photo: Håkan Wallander)
Lund University, Deparment of Physical Geography and Ecosystem Science
Soils and soil processes – decisive for feeding the world Example 4: Ecological agriculture or fertilizers to feed an
increasing world population (9 000 000 000 in 2050)?
Ecological agriculture: +Creates more fertile soils +More biodiversity… -Reduced crops (ca 1/5 lower)
Agriculture with fertilizers: +More crops -Less fertile soils -Less biodiversity -Use of pesticides
(From ec.europa.eu)
What happens when we have emptied the P supplies (Peak phosphorous)?
Lund University, Deparment of Physical Geography and Ecosystem Science
Bedrock, regolith and soil
(From Hess, 2013)
Lund University, Deparment of Physical Geography and Ecosystem Science
Five factors for soil development
-The geologic factor -The climatic factor -The topographic factor -The biological factor -The time factor
Lund University, Deparment of Physical Geography and Ecosystem Science
The geologic factor
-Parent material often the dominating factor in early stages -Parent material could be bedrock or transported sediments -Chemical composition and physical properties depends on parent material
(From Hess, 2013)
Lund University, Deparment of Physical Geography and Ecosystem Science
The climatic factor
-Temperature and moisture accelerates chemical and biological processes
-Moving water carries dissolved chemicals and particles rearranging and providing nutrients
(From Hess, 2013)
Lund University, Deparment of Physical Geography and Ecosystem Science
The topographic factor
-Slope and drainage (erosion and runoff)
(From Hess, 2013)
Lund University, Deparment of Physical Geography and Ecosystem Science
The biological factor
-Organic matter: a source of nutrients
-Microorganisms, e.g. bacteria and funghi: Decomposition of organic matter, conversion of nutrients.
-Vegetation (including roots): Uptake of nutrients. Roots affects soil structure (drainage and aeration)
-Earth worms, ants etc: fertilizing, bioturbation
-Big animals: Grazing, compacting and dropping excreta.
The time factor
-The time required for soil formation depends on parent material and differs between different environments.
-Generally slow processes.
Lund University, Deparment of Physical Geography and Ecosystem Science
Soil components
-Inorganic materials -Organic matter -Soil air -Soil water
(From Hess, 2013)
Lund University, Deparment of Physical Geography and Ecosystem Science
Inorganic materials
-Pieces of minerals, different sized e.g. sand and silt
-Clay important for plant nutrition (large surface area, important nutrient attach on the particles)
(From Hess, 2013)
Lund University, Deparment of Physical Geography and Ecosystem Science
Organic matter – litter, humus and living organisms
(Photo: Cecilia Akselsson)
Lund University, Deparment of Physical Geography and Ecosystem Science
Soil water – different forms
-Gravitational water
-Capillary water (surface tension)
-Hygroscopic water (adhesion)
-Combined water (chemical bounds with soil minerals)
(From Hess, 2013)
Lund University, Deparment of Physical Geography and Ecosystem Science
The soil water budget: Precipitation - evapotranspiration
(From Hess, 2013)
Lund University, Deparment of Physical Geography and Ecosystem Science
Soil properties
-Color -Texture -Structure
Lund University, Deparment of Physical Geography and Ecosystem Science
Color
-Dark soils: often rich in organic material, high fertility
-Red/yellow soils: Iron oxides on the soil particles
-Grey/bluish: Poor drainage
-Light color: much leaching in wet areas, accumulation of salts in dry areas
(Photo: Cecilia Akselsson)
Lund University, Deparment of Physical Geography and Ecosystem Science
Texture
Swedish system: Bolder: > 200 mm
Stone: 6-200 mm
Gravel: 2-60 mm
Sand: 0.06-2 mm
Silt: 0.002-0.06 mm
Clay: < 0.002 mm
(http://www-markinfo.slu.se/)
Lund University, Deparment of Physical Geography and Ecosystem Science
Structure – affects porosity and permeability
(From Hess, 2013)
Lund University, Deparment of Physical Geography and Ecosystem Science
Soil chemistry Colloids: important for water and nutrients
-Soil particles smaller than 0.1 µm
-Inorganic colloids: clay
-Organic: humus (decomposed organic matter)
-Works like a sponge, soaks up water
-Attracts a large amount of ions
Lund University, Deparment of Physical Geography and Ecosystem Science
Soil chemistry Cation exchange on colloids
-Negative colloids attract positive ions, e.g. Ca, Mg and K, which are important nutrients
-Ca, Mg and K easily exchanged by e.g. H (cation exchange)
-Cation exchange capacity (CEC): The ability of a soil to attract cations
-High CEC – fertile soils (high contents of clay and humus)
Lund University, Deparment of Physical Geography and Ecosystem Science
Soil chemistry Acidity/alkalinity
-Acid: Produces H+ when dissolved (acidic solution)
-Base: Produces OH - when dissolved (alkaline solution)
-Basic solution: Low release of nutrients (dissolving minerals)
-Acid solution: Faster release of nutrients
Lund University, Deparment of Physical Geography and Ecosystem Science
Mini exercise: How would you describe the soils from where you come
-Color -Texture -Structure -Other properties
Lund University, Deparment of Physical Geography and Ecosystem Science
Soil horizons – a result of soil formation processes
(From Hess, 2013)
Lund University, Deparment of Physical Geography and Ecosystem Science
Processes in soil formation
-The 5 soil forming factors influence the rate of addition, loss, transloca- tion and transformation
-Soil profiles with soil horizons are created
(From Hess, 2013)
Lund University, Deparment of Physical Geography and Ecosystem Science
Pedogenic (soil-forming) regimes
(From Hess, 2013)
Lund University, Deparment of Physical Geography and Ecosystem Science
Laterization (Lateritisering)
-Warm and moist regions (tropics and subtropics)
-Fast weathering, decomposition
-Most mineral leach, leaving Fe and Al oxides and quartz sand
(From Hess, 2013)
Lund University, Deparment of Physical Geography and Ecosystem Science
Gleization (“Försumpning”)
-Waterlogged areas (flat land/regression/high water table), cool climate
-Highly organic A horizon
-Iron is reduced (from 3+ to 2+) and leached away
Lund University, Deparment of Physical Geography and Ecosystem Science
Podzolization (Podsolisering)
-Positive moisture balance, cool regions (boreal forests in subarctic environments)
-Slow weathering, limited nutrient requirements, acid litter
-Leaching due to high precipitation and lots of acids: Fe and Al oxides and other elements leaches, creates a bleached layer and a layer enriched in the leached elements
Photo: Cecilia Akselsson
Lund University, Deparment of Physical Geography and Ecosystem Science
Calcification (Kalcifikation)
-Semiarid and arid areas with grasses and shrubs (e.g. prairies of North America, steppes of Euroasia), less precipitation than potential evapotranspiration, no or little leaching
-Ca salts produced
Lund University, Deparment of Physical Geography and Ecosystem Science
Salinization (Försaltning)
-Inadequate drainage, intense evapotranspiration in arid and semiarid regions, ground water comes up through capillary forces
-Toxic salts in the upper layers – not much life
(From Hess, 2013)
Lund University, Deparment of Physical Geography and Ecosystem Science
Soil types (jordmåner)
-“the parts of the earth crust's surface layer, that during different eras have been influenced by climate and organisms.” Source: Nationalencyklopedin (the Swedish National encyclopaedia). -can give information about soil quality, sensitivity, applicability and management requirements
(Photo: Cecilia Akselsson)
Lund University, Deparment of Physical Geography and Ecosystem Science
Soil classification: different systems
-US system (in the book) -FAO system -National system, Sweden
(Photo: Cecilia Akselsson)
Lund University, Deparment of Physical Geography and Ecosystem Science
Soil classification: US system – The soil taxonomy
-12 soil orders, many suborders, more levels… -Some examples of orders: Spodosols, Inceptisols, Entisols and Histosols -Applied in the US, but is very general and is often used world-wide
(Photo: Cecilia Akselsson)
Lund University, Deparment of Physical Geography and Ecosystem Science
Soil classification: US system – The soil taxonomy
(From Hess, 2013)
Lund University, Deparment of Physical Geography and Ecosystem Science
-28 main groups, divided into subgroups -Some examples of groups: Podsols, Cambisols, Histosols, Gleysols, Leptosols, Regosols och Arenosols. -Applied in Sweden (Swedish Survey of Forest Soils), together with the national system
Soil classification: FAO – Soil map of the world
(Photo: Cecilia Akselsson)
Lund University, Deparment of Physical Geography and Ecosystem Science
Soil classification: FAO – Soil map of the world
(http://www-markinfo.slu.se/)
Lund University, Deparment of Physical Geography and Ecosystem Science
National system, Sweden
-13 soil types -Covers e.g. different forms of podsols, brown forest soils, waterlogged soils and lithosoles -Applied in Sweden (Swedish Survey of Forest Soils), together with the FAO system
(Photo: Cecilia Akselsson)
Lund University, Deparment of Physical Geography and Ecosystem Science
National system, Sweden
(http://www-markinfo.slu.se/)
Lund University, Deparment of Physical Geography and Ecosystem Science
National system, Sweden – Iron podsol
-Organic layer -Light layer, weathered, mostly quartz left -Reddish layer, enriched in substances from above, e.g. Fe compounds
(http://www-markinfo.slu.se/)
Lund University, Deparment of Physical Geography and Ecosystem Science
National system, Sweden – Brown forest soil (Brunjord)
-No sharp boudaries between layers, mixed by earth worms
(http://www-markinfo.slu.se/)
Lund University, Deparment of Physical Geography and Ecosystem Science
National system, Sweden – Transition (övergång)type
-In between podzol and brown forest soil
(http://www-markinfo.slu.se/)
Lund University, Deparment of Physical Geography and Ecosystem Science
National system, Sweden – Lithosols
-Thin layer of organic soil horizon/ mineral soil (max 10 cm)
(http://www-markinfo.slu.se/)
Lund University, Deparment of Physical Geography and Ecosystem Science
Wrapping up minerals and soils – What have you learnt?
• three types of rock
• many soil types
• rock and soil consist of minerals
• weathering turns rock into soil and finally leads to release of nutrients
• parent material and climate are the most important factors for soil fertility
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