Textbook Notes (381,335)
CA (168,503)
UTSC (19,326)
EESA01H3 (82)
Chapter 7

CHAPTER 7 DETAILED NOTES FOR 4.0

14 Pages
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Department
Environmental Science
Course Code
EESA01H3
Professor
Carl Mitchell

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Soil as a system
Soil is a complex plant-supporting system consisting of disintegrated rock, organic
matter, water, gases, nutrients, and microorganisms.
oFundamental to the support of life on this planet and the provision of food
fort he growing human population
The composition of a regions soil can have as much influence on the regions
ecosystems as do the climate, latitude and elevation.
Soil is composed of living and non living components
Soil formation is slow and complex
Parent material is the base of geological material in a particular location.
oCan include lava or volcanic ash; rock or sediment deposited by glaciers,
sediment doposited by rivers, or bedrock, the continuous mass of solid rock
that makes up Earths crust.
Weathering, erosion, and the deposition of organic matter were responsible for soil
formation.
Weathering describes the physical, chemical, and biological processes that breaks
down rocks and minerals, turning large particles into smaller particles.
Physical Weathering or mechanical weathering breaks down rock without
triggering a chemical change in the parent material
oWind and rain are two main forces.
oAreas with extreme temperature fluctuations experience rapid rates of
physical weathering.
oWater freezing and expanding in cracks in rock also causes physical
weathering
Chemical weathering results when water or other substances chemically interact
with parent material.
oEg. Groundwater being unusually acidic.
Biological weathering occurs when living things break down parent material by
physical or chemical means.
oTree accelerates weathering by physical action of its root growing and
rubbing against rock.
Erosion is the movement of soil from one area to another
www.notesolution.com
oThis is physical weathering
oA destructive process that reduces the amount of life that a given area of land
can support.
Partial decomposition of organic matter creates humus a dark, spongy, crumbly
mass of material made up of complex organic compounds.
oSoils with high humus content hold moisture well and are productive for
plant life.
Soil that are dominated by partially decayed, compressed organic material are called
peat.
oPeat is characteristic of northern climates because cool temperatures slow the
decay process, allowing great thicknesses of organic material to accumulate.
5 primary factors that influence the formation of soil (table 7.1 page 192)
oClimate
Soil forms faster in warm wet climates. Heat speeds chemical
reactions and accelerates weathering, decomposition, and biological
growth.
oOrganisms
Earthworms and other animals mix and aerate soil, add organic
matter. Plants add organic matter
oTopograhpic relief
Steeper slopes result in more runoff as an example
oParent Material
Chemical and physical attributes of the parent material influence
properties of the resulting soil
oTime
Soil formation takes decades, centuries, or mellenia
Multiple factors (including the 4 above)
A soil profile consists of layers known as horizons
Each layer of soil is known as a horizon
the cross section as a whole, from surface to bedrock is known as a soil profile
www.notesolution.com
Five major horizons, O, A, B, C & R
Few soils contain all the horizons
O (organic) horizon is an uppermost layer consisting mostly of organic matter,
such as decomposing branches, leaves and animal waste.
A horizon is under the organic horizon and consists of inorganic mineral
components, with organic matter and humus from above mixed in.
oRefered to as topsoil
oMost nutritive for plans and most vital for ecosystems and agriculture.
oTakes its loose texture and dark colour from its humus contents.
The O and A horizons are home to most of the countless organisms that give life to
soil.
Degree of weathering and concentration of organic matter decrease as you go down
the soil profile from the surface
Minerals are carried downward as a result of leaching (the process whereby solid
particles suspended or dissolved in liquid are transported to another location)
oE.g. coffee grounds in a drip fiter.
oMinerals that leach rapidly from soils can be carried into groundwater and
can pose human health threats when the water is extracted
B horizon
obelow A horizon
C horizon
oLocated below B
oConsists of parent material unaltered or only slightly altered by the process
of soil formation.
R (rock) horizon lays at the bottom.
Certain soils are characterized by the presence of water (W horizon)
oSome arctic soils for example contain a segregated layer of perennially frozen
ice or permafrost
Soil can be characterized by colour, texture, structure and pH
www.notesolution.com

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Description
Soil as a system Soil is a complex plant-supporting system consisting of disintegrated rock, organic matter, water, gases, nutrients, and microorganisms. o Fundamental to the support of life on this planet and the provision of food fort he growing human population The composition of a regions soil can have as much influence on the regions ecosystems as do the climate, latitude and elevation. Soil is composed of living and non living components Soil formation is slow and complex Parent material is the base of geological material in a particular location. o Can include lava or volcanic ash; rock or sediment deposited by glaciers, sediment doposited by rivers, or bedrock, the continuous mass of solid rock that makes up Earths crust. Weathering, erosion, and the deposition of organic matter were responsible for soil formation. Weathering describes the physical, chemical, and biological processes that breaks down rocks and minerals, turning large particles into smaller particles. Physical Weathering or mechanical weathering breaks down rock without triggering a chemical change in the parent material o Wind and rain are two main forces. o Areas with extreme temperature fluctuations experience rapid rates of physical weathering. o Water freezing and expanding in cracks in rock also causes physical weathering Chemical weathering results when water or other substances chemically interact with parent material. o Eg. Groundwater being unusually acidic. Biological weathering occurs when living things break down parent material by physical or chemical means. o Tree accelerates weathering by physical action of its root growing and rubbing against rock. Erosion is the movement of soil from one area to another www.notesolution.com o This is physical weathering o A destructive process that reduces the amount of life that a given area of land can support. Partial decomposition of organic matter creates humus a dark, spongy, crumbly mass of material made up of complex organic compounds. o Soils with high humus content hold moisture well and are productive for plant life. Soil that are dominated by partially decayed, compressed organic material are called peat. o Peat is characteristic of northern climates because cool temperatures slow the decay process, allowing great thicknesses of organic material to accumulate. 5 primary factors that influence the formation of soil (table 7.1 page 192) o Climate Soil forms faster in warm wet climates. Heat speeds chemical reactions and accelerates weathering, decomposition, and biological growth. o Organisms Earthworms and other animals mix and aerate soil, add organic matter. Plants add organic matter o Topograhpic relief Steeper slopes result in more runoff as an example o Parent Material Chemical and physical attributes of the parent material influence properties of the resulting soil o Time Soil formation takes decades, centuries, or mellenia Multiple factors (including the 4 above) A soil profile consists of layers known as horizons Each layer of soil is known as a horizon the cross section as a whole, from surface to bedrock is known as a soil profile www.notesolution.com
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