lecture 10 Flashcards
What does the term terrestrial environment refer to?
Terrestrial environment refers to land based ecosystems, where living organisms (biotic components) interact with non-living (abiotic) factors such as soil, rock, and air.
How much of earth’s surface do terrestrial environments cover?
Terrestrial environments cover 29% of Earth’s total surface area, while the remaining 71%
is covered by water.
How much of the earth’s crust is the geosphere? What’s it composed of?
the outer 40 km of Earth’s crust, is primarily composed of rocks and soil
Why is the study of soil important?
It’s the link between air, water, rocks, and organisms and is responsible for many diff functions that we couldn’t survive w out
What functions is soil responsible for?
Carbon and nutrient cycling (GBEC)
* Agriculture and forestry
* Water cycling and quality
* Natural waste decomposition
* Home for many organisms (e.g., microbes, insects)
What is soil?
soil is a product of the weathering of rocks by physical, chemical, and biological processes that give a medium that can support plant growth
What are the four major phases of soil?
1) Finely divided mineral matter
2) various levels of organic matter
3) Water
4) Air
What kind of mixture is soil?
Is a three-phase mixture, solid, gas, li
A complete description of soil in environmental reactions involves what?
All 3 phases of soil
Is soil renewable?
No, takes 200-400 years to produce 1 cm of soil in a location
Do all soils have organic matter?
No
What does the water in soils do?
It is responsible for transporting nutrients
What are the soil profiles?
O(surface layer) A(topsoil) B(subsoil) C(parent material) D(bedrock)
Why is there different colors in a soil profile?
Because rain percolates and leaches soil, carrying soluble and colloidal (0.001-1.0 um) of material lower into soil, this results in the development of banded layers or horizons
What is the main component of soil? second most?
silicate minerals, aluminum
What are the four major components of soil?
1) Finely divided mineral matter (variable in size & composition)
2) various levels of organic matter (1-6%)
3) Water
4) Air
What is the finely divided mineral matter coming from?
Primary (quartz, feldspar, biotite)
secondary (silicate clay and iron oxide)
inorganic matter (silicate minerals)
How do silicate minerals lead to diff structures?
due to their tetrahedral shape
Why are clays important?
Clay particles are much smaller than sand/silt, their total surface area per gram is 1000x larger
The most important surface processes occur where?
On the surface of colloidal clay particles
What are the soil particles sizes, smallest to biggest?
clay, silt, sand (fine and coarse), gravel
What are clays? (6)
are aluminosilicates
* some of the most important minerals
* are natural water barriers & used as landfill liners
* constitute large component of soils
* are important in interaction between inorganics & organics
* form sheet-like structures
Name three examples of clay minerals
illite, kaolinite, montmorillonite
Silica is attached to how many OH?
4
Alumina is attached to how many OH?
6
What is the structure of Kaolinite?
is a single sheet of silica tetrahedron and a single sheet of alumina octrahedron bonded together by strong H-bonds
What is illite?
is a sheet of aluminum octahedron sandwiched by two sheets of silica tetrahedron. These layers are weakly bond together by K+ ion which stops water from getting through
What montomorillonite structure?
has one aluminum layer sandwiched between two sheets of silica. between these layers, water molecules are there which produce weak bonding. On the surface in the interlayer space, cations are bound due to negative charges at the surface by replacing Si4+ with Al3+, which then get replaced by Fe2+ and Mg2+. These cations are exchnagebale
What are physical properties of montomorillonite due to it’s large cation exchange capacity?
It can bind water, swell, and is liner in landfills
What is weathering?
Complex processes by which rocks on earth’s surface are transformed into soils are collectively known as weathering
How is soil weathered physically?
Temperature
Erosion & deposition by wind, water & ice
Plants and animal influence
How is soil weathered chemicially?
Through decomp, hydration, acid-base rxns, hydrolysis, complexation rxns, redox rxns
How does weathering by hydration occur?
you add water molecules to the rocks minerals, works with secondary minerals. The minerals swell and increase in volume and then become soft and lose their luster
Give examples of hydration via weathering?
Hematitie becomes limonite
Bauxite becomes hyd aluminum oxide
anhydrite becomes gypsum
How does weathering by carbonation occur?
Carbon dioxide dissolves in water and becomes carbonic acid, this carbonic acid attacks rocks (limestone) and minerals and puts them into solution
How does weathering by hydrolysis occur?
Water is a reactant, for example othoclase feldspar reacts with water to form kaolinite (secondary mineral), can react again to form gibbsite
How does weathering occur in regards to the abundant rainfall in the tropics?
silicic acid is soluble and results in red soils depleted in silica, but rich in kaolinite, aluminum, and iron hydroxides
In general what happens to aluminosilicates that are weathered by hydrlolysis?
Aluminosilicate + H3O+(aq) + H2O(aq) → clay mineral(s) + H4SiO4(aq) + cation(aq)
What is weathering by complexation?
Iron and aluminum form insoluble hydroxides in water, but these become soluble through soluble organic complexes (iron and aluminum bind with soil organic matter)
How much of soluble iron and aluminum in soil is present in the form of organic complexes?
More than 90%
How does weathering by oxidation and reduction occur?
primary minerals with elements in low oxidation states are exposed to the atmosphere and their oxidation state increases which then:
disturbs charge balance of the mineral, loss or gain of other elements to maintain neutrality, and then formation of secondary minerals
What is an example of oxidation/reduction weathering?
oxidation of iron in the primary mineral biotite from Fe2+ to Fe3+ produces the clay mineral vermiculite as potassium is lost
What is biological weathering?
is the weakening and subsequent disintegration of rock by plants,
animals and microbes.
How do growing plant roots contribute to weathering?
exert stress or pressure on rock
plant roots or microorganisms
produce organic acids which help to dissolve minerals
How does microbial activity contribute to biological weathering?
breaks down rock minerals by altering the rock’s chemical composition,
thus making it more susceptible to weathering.
Give an example of biological weathering involving microbial activity?
One example of microbial activity is lichen;
lichen is fungi and algae, living together in a symbiotic relationship. Fungi release
chemicals that break down rock minerals; the minerals are
consumed by the algae. As this process continues, holes and gaps continue to develop on the
rock, exposing the rock further to physical and chemical weathering
How do burrowing animals contribute to weathering?
They can move rock fragments to the surface, exposing the rock to more chemical, physical and bioligcal processes
What are the three physical properties of soil?
size
texture
permeability
What is the particle size of soils?
soils are made up of different particle sizes, can be subdivided based on these
Soils that are rich in clay are what?
heavy & poor
drainage and
aeration
Soils that are rich in sand are what?
have good drainage, poor water retention, araeted, and are primarily composed of primary minerals (quartz feldspar), are a poor source of nutrients
Clay particles act as what in water?
colloids
The best agricultural soils consist of what?
a combination of soil types
What the difference between clay mineral versus clay sized particles
minerals are acc silica and aluminum structures (kaolinite, and montomorillonite)
sized particles can be composed of clay minerals, organic matter, primary minerals, and iron and aluminum hydroxides, have large surface area, and can retain nutrients
What is soil texture?
A collective term that defines a soil by proportion of different particle
size components use soil triangle
Soils that fall in the middle of the soil triangle are what?
Soils that are desirable for agriculture
Soil permeability is what?
measure of ability of soil to conduct the flow of water
what is the consequences of a low permeable soil?
can become waterlogged, and has anaerobic conditions
What is CEC?
is is the ability of soil to attach and exchange cations, refers to the total amount of cations a soil can hold
Why is CEC on of the most measured properties of soils?
it reflects soil fertility and nutrient retention capacity
under acidic conditions what happens to the cation exchange capacity?
CEC sites may be occupied by H3O ions which results in less nutrient binding capacity and reduced ability to neutralize additional acidity
What is base saturation?
number of exchange sites occupied by Ca2++Mg2++K++Na+
divided by total number of exchange sites
×100%
Is a large base saturation value desirable?
yes as (soils with low CEC and/or base saturation susceptible to acidification)
What has high CEC? Low?
high in organic matter, low in clay minerals
What are the primary sources of organic matter in soils?
plant tissue (roots, leaves, branches etc)
bacteria, fungi, and protozoa and worms
top 15 cm of soil contain upto how much microorganisms?
0.5%
List soil types in order of lowest to highest organic matter?
temperate agrocultural soils, tropical, forest, and then peat
What is humus produced by?
The degradation of organic matter
What does humus consist of?
humin, humic acids, and fulvic acids
What is humin?
very large molecules (molecular weight of 100,000 to 10,000,000)
* not soluble in water at any pH level, very slow to break down
* within soil, improves structure, water-holding capacity, and stability
* function as a cation exchange system- plant nutrients
What is humic acids?
a smaller molecular size than humins (molecular weight of 50,000 to 100,000)
* soluble in water under alkaline conditions
* function as important ion exchange and chelating systems.
What is fulvic acids?
smaller than humic acids (molecular weight of 5,000 to 10,000)
* water soluble at all pH levels
* have a higher oxygen content than humic acids
* can easily enter plant roots, stems, and leaves, transporting trace minerals directly to metabolic sites in plant cells
Fulvic acids and humic acids can form what?
colloids
Fulvic acids and humic acids are what kind of strands and what do they contain?
Fulvic acids and humic acids are polymeric strands containing many -COOH and –OH groups
What are the general trends of fulvic to humin acid?
It increases in intensity of color
increases in degree of polymerization
increases in molecular weight
increases in carbon content
decrease sin oxygen
decreases in exchange acidity
decreases in degree of solubility
If soil is deficient in trace elements what happens to food and ultimately humans?
also gonna be deficient
How do we measure availability of elements in soil?
Soil is shaken with an aq solution containing chemicals that will displace the elements that are gonna be readily available for plants
What are colloidal materials?
An intermediate between particulate suspensions and solutions, they do not settle, and have unique surface properties that depend on the chemical nature of the colloid
Colloidal particles with negatively charged surface have what?
large surface area and attaraction for cations
Why are colloids of interest in soil?
Have a large surface area, have surface ion exchnage, can do cation immobilization and transport of nutrients and pollutants
Why do colloidals have large surface area?
do to small size
Why do colloidals have negative charge?
clays have negative surface charge that is relatively constant in magnitude, humic materials are ph dependent on charge but at normal ph are negative
What determines the soils pH?
Soils rich in carbonate minerals (e.g., dolomite) are usually somewhat alkaline
(~pH 8.7)
* Soils with large amounts of Humic Materials (HM) tend to be acidic (~pH 4.6)
* Acidity arises from microbial decomposition of organic matter producing
organic acids as a metabolic end product + CO2
* Soil pH also affected by redox status of soil:
* If soil containing Fe(OH)3 submerged → used for oxidation of {CH2O}
FeIII(OH)3 (s) + 3 H3O+(aq) + e- → Fe2+(aq) + 6 H2O
because H3O+ consumed in reaction → rise in pH
