Exam #1 Flashcards
what is soil made of?
45% minerals
25% air
25% water
5% organic matter
an average soil is composed of ____ pore space found between particles
50%
what are the five plant growth factors?
light, temperature, water, nutrients, and genetics
define “soil”
the material; mixture of minerals, gases, water, organic matter, and organisms capable of supporting plant life
define “a soil”
an individual natural body (organized, 3-dimensional, region/biome specific, and has distinct characteristics.
define “the soil”
all of the soils (natural bodies). soil the material, roots, ground dwelling animals and rocks.
the soil (all of the soils) is also called the ______
pedosphere
what are the four spheres of the pedosphere? (spheres are always intertwined)
1) atmosphere/soil air (CO2, O2 and N2)
2) biosphere/organic matter and biomass (plants, animals, microbes)
3) hydrosphere/soil water (water and dissolved substances)
4) lithosphere/soil particles (minerals in rocks, clay and sediments)
soils have layers called what?
horizons (O horizon, A horizon, B horizon, C horizon and bedrock)
how long does it take for 1 in of topsoil to form?
500-1000 years
soil quality is determined by its capacity to….
provide ecosystem services
what are ecosystem services?
products and functions of natural systems that support and fulfill the needs of humans
what are the six ecosystem services provided by soils?
1) plant medium growth (nutrients, physical support, root aeration, moisture supply and storage, temperature regulation, and protection from toxins)
2) provides and recycles nutrients (mineral weathering releases nutrients from unavailable storage forms)
3) regulates the atmosphere (huge carbon pool or sink)
4) provides hidden habitat (bacteria, fungi, insects, earthworms, etc)
5) serves as an engineering medium (building infrastructure)
6) nature’s rain barrel (storage) and water filter
is soil a renewable or a non-renewable resource?
non-renewable
what is soil degradation?
reduction is soil quality
what are the causes of soil degradation?
erosion, nutrient depletion, organic matter depletion, compaction, acidification, and salt accumulation
what percentage of soils have been degraded?
33% of global soils
soil restoration is key to _______
agroecosystem restoration
where does soil form?
Earth’s crust, upper lithosphere (and uppermost solid mantle)
what is the critical zone?
top of tree canopy to the water table
soil is the heart of the _______ _____
critical zone
Igneous rocks forms…
during cooling and crystallization of lava or magma
Sedimentary rocks forms…
from cementation (lithification) of sediments (small rock fragments)
Metamorphic rocks forms…
when igneous or sedimentary rocks are altered under high heat and pressure conditions found deep in Earth’s crust
what is the rock cycle? draw it
When igneous rocks are eroded by
wind, water or ice, and the resulting particles are deposited elsewhere and cemented, they become sedimentary rocks. Sedimentary and igneous rocks exposed to extreme heat and pressure become
metamorphic as their minerals re-crystalize. Metamorphic rocks can become sedimentary rocks in the same way as igneous rocks can. In reality, multiple kinds of igneous and/or metamorphic rocks can
combine to make sedimentary rocks.
Mafic vs. felsic minerals in Igneous rocks
felsic = increasing Si (silicon)
Mafic = increasing Fe, Mg, and Ca (iron, magnesium, and calcium)
intrusive vs. extrusive minerals in Igneous rocks
intrusive = slower cooling, coarse grained, and tends to have a more spotted look.
extrusive = faster cooling, fine grained, and tends to have a homogenous look.
primary minerals form…
during cooling of magma
secondary minerals form…
from chemical breakdown or alteration of primary minerals
what are examples of primary and secondary minerals?
primary minerals: quartz, feldspar
secondary minerals: calcite, clay minerals, Gibbsite
what mineral type forms during weathering?
secondary minerals
what is weathering?
all physical and chemical changes produced in rocks or minerals. occurs at or near the earth’s surface. facilitated by air, water, and organisms.
what is physical weathering?
breakdown or disintegration of larger rocks or rock fragments into smaller particles by physical force.
what is chemical (biogeo) weathering?
alteration and/or breakdown of initial mineral compounds through chemical reactions.
what are the four main physical weathering agents?
1) temperature (expansion, contraction, and exfoliation)
2) wind (erosion)
3) water and ice (erosion, freeze-thaw, and shrink-swell)
4) biota (plant roots, animals digging or walking)
what is exfoliation?
“peeling of rock” (usually Igneous) from outside in, caused by temperature and pressure changes. temp + pressure: expansion + contraction –> exfoliation (ex: Half Dome, Yosemite National Park)
when is biogeochemical weathering faster and slower and why?
chemical weathering is faster in warm and wet climates and slower in cold and dry climates. this is because the rocks are undergoing a chemical reaction that utilizes water either as a reactant or to dissolve and diffuse reactants. additionally, in higher temperature conditions, more collisions occur on the molecular level so it will occur faster.
describe freeze-thaw in terms of physical weathering
when water freezes into ice it expands and this expansion of water breaks sedimentary rocks into even smaller particles.
describe ice lenses in terms of physical weathering
nearby liquid water flows from wet to dry (icy) areas of soil. once the liquid touches the cold ice, its temp decreases causing some liquid water to freeze. as it freezes, the ice expands, pushing against nearby rocks and soil. this can crack open rocks, break up clumps of soil or push clumps of soil together.
do ice lenses or freeze-thaw result in more weathering?
ice lenses
how might streams or flowing water cause physical weathering?
smaller rocks in streams may tumble, roll, skip and bounce, scrape against each other, and hit larger rocks in the streambed.
how does wind cause physical weathering?
sand and other small particles get carried in the wind and over time those particles scrape and score against the outside of rocks and abrade them into smaller particles
how do plant roots cause physical weathering?
when plant roots grow and expand into the ground, they help crack open rocks and compress surrounding sediments and soils. they also make rocks push against other rocks which causes weathering
how do animals cause physical weathering?
animals cause physical weathering by burrowing, crawling/walking, and digging.
what are the 3 soil particle sizes?
(largest) sand –> silt –> clay (smallest). sand can weather into silt which can weather into clay. more physical weathering = more silt and clay particles.
what are the 6 types of chemical weathering reactions?
1) Hydration (w/ water)
2) Hydrolysis (w/ water)
3) Dissolution (w/ water)
4) Acid-base
5) Complexation
6) Redox
what is hydration?
process of adding water to chemical structure without forming covalent or ionic bonds with the rest of the structure
what is hydrolysis?
splitting water, the add H+ or OH- to mineral.
what is dissolution?
solubilize in water (surrounded by water molecules)
what are acid-base reactions?
acid donates H+ to base
what is carbonation?
an example of an acid-base reaction. dissolution of CO2; produces carbonic acid
what is complexation?
electronegative nonmental compounds (ligands) surrounding and bonding to a metal.
what are redox reactions?
electrons get donated from one molecule to another.
what types of rocks weather faster vs. slower?
sedimentary rocks weather faster than igneous rocks and metamorphic rocks
what types of minerals weather faster vs. slower?
felsic (Si) minerals weather slower than mafic (Fe) minerals. Mafic has more Fe (iron) = faster redox reactions = faster weathering
how might chemical and physical weathering affect one another?
the physical weathering increases surface area which allows more contact with water molecules. chemical weathering destructs and creates a weak spot which allows physical weathering to occur easier.
what happens to minerals dissolved in chemical weathering?
they form weathered minerals and ions which then either leach to groundwater, transport to streams and oceans, or precipitate to form secondary minerals
the Jenny equation describes what
the 5 factors of soil formation
what is the Jenny equation?
Si = f (cl, o, r, p, t)
Si = individual soil property
cl = climate (temp + precipitation)
o = organism (biota: microbes, vegetation, animals)
r = relief or topography (slope, aspect, landscape position)
p = parent materials (geological or organic precursors to soil)
t = time (how much time elapsed since parent materials began weathering)
which soil formation factor is a multiplier of 3 of the other factors?
time; the longer a soil has to form, the longer climate and organisms act upon each other and change the parent materials
what are the three general categories of parent materials?
1) organic
2) residual
3) transported
what are organic parent materials?
Organic Parent material = mostly dead and slowly decomposing plants (ex: peat + muck)
organic = of biological origin; contains carbon (C-C & C-H bonds)
what climate are organic plant materials typically found in?
cool, wet climates (wetlands). decomposition is much slower with a lack of oxygen and warmth. (common in Arctic and sub-Arctic regions)
what is the compositional difference between mineral soil and organic soil?
mineral soil = less than 20% organic matter (~99% of world’s soils)
organic soil = more than 20% organic matter (~1% of world’s soils)
how does mineral soil vs organic soil differ visually?
Mineral soils are typically much lighter in color than organic soils. Organic matter is very dark brown, almost black. Dark colored soils usually contain large amounts of organic matter, lighter soils less
organic matter
what are residual parent materials (Residium)?
parent material directly from solid bedrock (residual = left behind)
what are the four vectors for transported parent materials?
1) water
2) ice
3) gravity
4) wind
what is the term for stream-deposited parent materials?
Alluvium // alluvial parent material
(well sorted, rounded fragments because they’re being tumbled for long periods)
what is the term for lake-depositied parent materials?
Lacustrine
what is the term for gravity deposited parent materials?
Colluvium = colluvial parent materials. usually found at the bottom of mountains and hills. (poorly sorted because gravity acts the same on all rocks) (angular fragments because they usually break apart abruptly and they don’t “tumble” downwards for very long)
what is the term for ocean deposited parent materials?
marine parent materials. found in coastal areas and is mostly sandy; some silt and clay.
what is the term for ice deposited parent materials?
glacial till (poorly sorted materials because ice will plow and pick up everything without any order or reason, ice also grinds up rocks at the bottom)
glacial outwash parent materials occur when glaciers melt. is this considered glacial till or alluvium at that point?
alluvium parent materials because it’s deposited by water (glacial stream)
what is the term for wind deposited parent materials?
Eolian/Aeolian (think Sand Dunes, usually occurs in dry places). windblown silt sized particles are called Loess, and they are small enough to be moved considerable distances before being deposited)
what is the difference between sand and Loess?
sand = .5-2mm (water flows too fast between the sand particles so water doesn’t stay, and plants are scarce)
Loess = silt sediments = .02-.5mm (water flows much slower so silt sediments hold onto water better, hence allowing for more plants to survive)
how does the parent materials affect soil properties?
1) the younger the soil, the more soil properties will resemble the parent material (time)
2) as the weathering rate increases, soil thickness increases along with percent secondary minerals
3) initially soil particles resemble parent material in both mineral and particle size
how are temperature and reaction rates related to one another?
for every 10 degrees C increase in temperature, the reaction rate doubles (2x faster)
what is effective precipitation?
amount of rain/snow/hail reaching the parent material
more intense rainfall means a ______ rate of weathering
higher. more water is reaching the parent material
more transpiration and evaporation relative to precipitation means a _______ rate of weathering
slower. less water is reaching that parent material underground
if there is a slope, where does the most effective precipitation occur?
lower on the slope of the landscape. higher weathering rate occurs at lower slopes because water is moving from higher slopes and shedding into lower sloped areas
how does particle size affect the rate of weathering and effective precipitation?
the larger the particle size, the more water that is sinking deeper into the soil which results in a higher amount of weathering deep in the soil
what is the global aridity index?
the ratio of precipitation to potential evapotranspiration
soil depth increases with increasing …
temperature and precipitation. therefore, in arid climates the range of depth for the lower boundary of rock weathering is very shallow (<10m) and in humid climates the, the range of depth for rock weathering is much deeper (25-60m)
soil depth increases with ….
increasing weathering
what types of organisms (biota) affect soil?
1) plants
2) microbes and soil animals
3) humans
what is bioturbation?
the mixing of soil by organisms
generally, explain the affect plants generally have on soil
-plants influence organic matter accumulation, erosion rates, and physical and chemical weathering. plant roots absorb moisture from the soil which decreases the rate of chemical weathering. plants are also the primary source of organic matter in soils.
explain the affect microbes and soil animals have on soils
burrowing organisms mix the soil horizons (layers) together and aid in nutrient recycling which is called bioturbation. they also aid in organic matter breakdown and accumulation. they also provide soil stability and structure.
explain the affect humans have on soil weathering
-humans create mixing (tillage) in the soil.
-humans put pavement over the soil which is called soil sealing
-turning soils into landfills
tends to be destructive, not usually great but does depend on management practices
when thinking about plants altering soils, what two factors should you consider
type of vegetation (trees vs. grasses) and climate (wet vs. dry, cold vs. warm)
in grassland communities, plants produce _____ acid, resulting in a _____ pH and ____ earthworms which _____ the mixing of organic matter into topsoil which results in a _____ topsoil
less, higher, more, increases, thicker
in grassland communities, less acid means ____ leaching and ____ Ca. a _____ root turnover = _____ organic matter added to the soil.
less, more.
faster, more
tree roots produce more _____ than grassland roots do and they live _____
acid, longer
in tree dominant communities, plants produce _____ acid, resulting in a _____ pH and ____ earthworms which _____ the mixing of organic matter into topsoil which results in a _____ topsoil and _____ leaf litter
more, lower, less, decreases, thinner, thicker
in tree communities, more acid means ____ leaching and ____ Ca. a _____ root turnover = _____ organic matter added to the soil.
more, less.
slower, less
