SOILS AND MINERALS

Unit 5

What is soil? Relatively thin surface layer of the Earth’s crust Consists of mineral and organic matter that has

been modified by natural actions of agents such as weather, wind, water, and organisms

VERY important many organisms live there and terrestrial plants could not survive without it

How is soil formed? From parent material (usually rock) that is

slowly fragmented (broken down) into smaller and smaller particles

Weathering processes = biological, chemical, or physical processes that break down rocks can take a very long time, sometimes thousands of years

What affects weathering processes? Organisms = Plant roots, insects,

bacteria, etc.Respiration produces CO2, which diffuses

into the soil and reacts with soil water to form carbonic acid (H2CO3)

Other acids form cracks in rock, which fill with water freezing and thawing

Climate = precipitation, temperature (freezing and thawing), wind currents, etc.

Topography A region’s surface features mountains,

valleys, etc. Steeper slopes have little or no soil on

them, more runoff, and more erosion Moderate slopes and valleys tend to

have deep soils

Typical Soil Composition 45% mineral particles – from weathered

rock 5% organic matter 25% water 25% air

Terms to know… Humus = Partly decomposed organic

material in the soil; brown or black in color

Leaching = Movement of water and dissolved material downward through the soil

Illuviation = Deposition of a material into a lower soil layer from a higher layer as a result of leaching

Terms to know… Sand = Large (0.05 – 2 mm in diameter) inorganic

particles in the soil; coarse enough to feel gritty Silt = Medium sized (0.002 – 0.05 mm in diameter)

inorganic particles in the soil; too small to feel gritty Clay = Small (<0.002 mm in diameter) inorganic

partilces in the soil; too small to settle out of suspension

Terms to know… Soil water = water that fills

the pores (spaces) between soil particles; can originate as precipitation or groundwater

Soil air = air that fills the pores between soil particles; usually has the same gases as atmospheric air, but with more carbon dioxide and less oxygen

Soil Horizons Distinctive horizontal layers

in soil Soil profile = a vertical

section from surface to parent material that shows the soil horizons

Soil Horizons O horizon = uppermost

layer of soil, rich in organic material

A horizon = topsoil, dark and rich in organic material and humus, tends to be granular and nutrient poor due to leaching

Soil Horizons E horizon = sometimes

occurs between A and B horizons, very heavily leached, not always present

B horizon = light colored subsoil, often a zone of illuviation where minerals and nutrients accumulate, usually rich in iron, aluminum, and clay

Soil Horizons C horizon = weathered

pieces of rock, below most roots, usually saturated with groundwater

Bedrock = original parent material that the soil rests on

Soil Properties Texture = determined

by proportions of sand, silt and clay

Loam = ideal agricultural soil, 40% sand, 40% silt, 20% clay

Soil triangle = tool used to classify soil

Soil Properties Charge = some are positively charged

(K+) or negatively charged (NO-3)

Clay particles are usually negatively charged

Soil Properties Soil acidity = measured on the pH scale (1-

14) 1-6.9 = Acid 7 = Neutral 7.1-14 = Base Close to 7 = weak Far from 7 = strong pH affects what minerals remain in the soil Optimum pH for plant growth = 6.0-7.0

Major Soil Groups Spodosols = form in colder

climates with a lot of precipitation and good drainage (ex. Coniferous forest)O horizon = acidic litter (mostly

needles)E horizon = ash-grey, acidicB horizon = dark brown

Too acidic and nutrient-poor to be good for agriculture

Major Soil Groups Alfisols = form in temperate

deciduous forestsA horizon = brown to grey-brownB horizon = contains most of the clay

and nutrients washed out of A and E horizons

If the deciduous forest is intact, soil fertility is maintained by continuous supply of plant litter

If soil is cleared for farmland, fertilizers must be used

Major Soil Groups Mollisols = primarily found in

temperate, semiarid grasslands; very fertileA horizon = thick, dark brown to

black, rich in humusPrecipitation is not enough to

leach nutrients to lower layersMost of worlds grain crops are

grown on mollisols

Major Soil Groups Aridisols = found in arid

regions; lack of precipitation and rich vegetation results in a lack of leaching and illuviation or distinct layers

Crops can be grown with irrigation

Rangeland for grazing animals

Major Soil Groups Oxisols = primarily found in

tropical and subtropical areas with a lot of precipitation, low in nutrient mineralsO horizon = little organic material

because leaves and twigs are rapidly decomposed

A horizon = rich in humusB horizon = thick, highly leached,

acidic, nutrient-poor

Major Soil Groups Pedalfers = found around here and in other temperate

regions that get significant rain; B horizons contain iron- and aluminum-rich materials red and orange

Pedocal = typical of dry climates like those found n the western United States; chemical weathering is slower. less clay; rich in calcium based minerals (calcite, limestone)

Laterite = form in hot, wet tropical areas; large amount of precipitation leaches out much of the silicate material making these soils orange and organically poor. One major reason for rainforest deforestation is the periodic need to replace the land exhausted by farming.

Major Soil Groups

Who lives in the soil? Millions of microorganisms

(bacteria, fungi, algae, microscopic worms, protozoa, etc.) can occupy 1teaspoon of fertile agricultural soil

Bigger organisms live there too plant roots, insects, earthworms, moles, snakes, groundhogs, etc.

Why are soil organisms important? They provide various ecosystem

services such as: Decaying and cycling organic materialPreventing erosionBreaking down toxic materialsCleansing waterAffecting the atmosphereCastings = bits of soil that have passed

through the gut of an earthworm, moving nutrients from deeper layers to the surface

Why are soil organisms important? Ants make tunnels and chambers that

aerate the soil They also bring food from the surface

down into the soil some of it decomposes and adds nutrients to the soil

Also bury seeds in soil grow into plants

Why are soil organisms important? Plants are affected by the properties of soil, and the soil is

affected by the plants that grow in it Mycorrhizae = associations between plants and fungi that

enable the plants to absorb enough nutrients and minerals Mycelium = tiny thread-like extensions of fungi that go

deeper into the soil than the roots of a plant, allowing the plant more access to nutrients and minerals and the fungi access to the food produced by photosynthesis

Nutrient Cycling Nutrients (like nitrogen and phosphorus)

cycle between soil and organisms Decomposition = bacteria and fungi Reabsorption = mainly plants Leaching Runoff Dust storms http://www.youtube.com/watch?v=gnp4Y

wjz-po

Soil Problems Human activities Erosion Mineral depletion

Sustainable soil use = using soil resources wisely without a reduction in the amount or fertility of the soil so that it is productive for future generations

Erosion The wearing away or removal of soil from the land Caused by water, wind, ice, etc. A natural process that can be accelerated by human

activity About 4.6 billion tons of soil are eroded from US

croplans and rangelands each year

Major Types of Erosion Surface erosion = rain, wind, frost, etc.

detach soil particles from the surface that are washed or blown away

Fluvial erosion = water gouges shallow channels or deep gullies in soil

Mass-movement erosion = gravity combines with heavy rain or earthquakes; whole slopes can slump, slip or slide

Stream bank erosion = not dramatic, can occur in regions where there is frequent flooding

Surface erosion Sheet erosion = rain falls on

bare or sparsely covered soil and moves loose material (silt, clay, humus) downhill soil loses fertility

Wind erosion = soil on surface is blown away, can form dunes, more severe if vegetation has been grazed or disturbed

Fluvial erosion Rill erosion = water runoff from shallow

slopes and gathers is small V-shaped channels or rills

Gully erosion = occurs on loose subsoils, they are deep and generate a lot of sediment, which is usually deposited into rivers

Tunnel gullying = water enters on a slope through cracks in the soil after a dry period, forming a tunnel that collapses on itself, forming a gully

Mass-movement erosion Slips = common where rock is

mudstone or siltstone, topsoil and subsoil becomes saturated and slides downhill

Earth flows = saturated soils move downhill, but vegetable mats are left behind

Scree erosion = occurs in steep mountainous areas, soil erodes in fan shapes

The American Dust Bowl The semi-arid prairie soil of the

American mid-west were cleared for crops and overgrazed by animals

The disturbance of the native vegetation left the soil vulnerable to erosion the fertile topsoil was removed by wind and water

The American Dust Bowl Dust could be seen as far as the east

coast and the Atlantic Ocean

Nutrient Mineral Depletion In a natural ecosystem, essential

nutrient minerals cycle between soil and organisms (especially plants)

Nutrients and minerals usually return to soil through decomposition

Harvesting crops stops this cycle soil is depleted of nutrients

Especially severe in rainforests

Soil Problems in the USA Rates of erosion measured every 5

years Good news: erosion is declining (since

1982) Bad news: erosion is still happening at

significant levels approximately 25% of agricultural lands in US are losing topsoil faster than it is being replaced

World Soil Problems 75 billion tons of topsoil lost each year,

especially in Asia, Africa, and Central and South America

Caused by the amount of agriculture needed to feed densely populated areas over-exploitation of soil

Solving Soil Problems… Conservation tillage = residues from previous

crops are left in the soil, covering it and keeping it in place

No-tillage = soil is undisturbed over the winter During planting, a narrow furrow is cut for

seeds Traditionally, soil would be cut and turned in the

spring, weeds would be removed, and seeds would be covered

Plant cover removed = more risk for erosion http://www.dailymotion.com/video/x6ie2l_benefits-of-conservation-tillage_tech

Solving Soil Problems… Crop rotation = planting a series of

different crops in the same field over a period of years

Same crop over and over = more pests accumulate, same nutrients get depleted

Solving Soil Problems… Contour plowing = plowing in

curved lines that conform to shape of land instead of straight lines

Strip cropping = alternating strips of different crops on natural contours

Terracing = making level areas on steep slopes for crops

Solving Soil Problems… Organic fertilizers = animal manure,

crop residue, bone meal, compost, etc. Slow acting, long lasting

Instead of… Commercial inorganic fertilizers =

manufactured from chemical compounds, exact chemical composition is known, but they are only available for a short time before they wash away

Solving Soil Problems… Shelter-belts = rows of trees between

fields that lessen the impact of wind

Soil Conservation Act of 1935 Authorized formation of Soil

Conservation Service Works with US citizens to conserve

natural resources on private lands Farmers tend to use less soil when

prices are lower, but more when prices are high

Food Security Act (Farm Bill) of 1985 Provisions for two main soil

conservation programs:Conservation compliance programConservation Reserve Program

Farmers with highly erodible land must develop a 5-year conservation plan, or lose federal subsidies

Conservation Reserve Program (CRP) Voluntary program that pays farmers

$50 per acre per year to stop producing crops on erodible farmland

Planting native grasses and “retiring” the land for 10 years

Very beneficial and effective

Grasslands Reserve Program (2002) Pays farmers to protect up to 2 million

acres of virgin and improved pastureland for at least 10 years

General Mining Law of 1872 Passed to encourage settlement in the western

states Allows companies or individuals (of any origin)

to stake mining claims on federal land, purchase the land for $2.50-$5 per acre, extract all valuable minerals from the land, and keep all the profits

In 1995, ASARCO obtained land with $2.9 billion worth of copper and silver for $1,745

Congress has since put a hold on all such sales (1996)

Minerals Elements or compounds of elements

that occur naturally in the Earth’s crust We use minerals for many things…

Steel, aluminum, copper, sulfur, sodium chloride, crushed limestone, silver, gold, etc.

Minerals Sulfides = mineral compounds combined with

sulfur Oxides = mineral compounds combined with

oxygen Rocks = naturally formed aggregates, or

mixtures, of minerals with varied chemical compositions

Ore = rock that contains a large enough concentration of a particular mineral that can be profitably mined and extractedHigh-grade ores and low-grade ores

Minerals Metals = minerals such as

iron, aluminum, copper, etc. They are malleable, lustrous, and good conductors of heat and electricity.

Nonmetallic minerals = minerals such as sand, stone, salt, phosphates, etc. that lack such qualities

Mineral Distribution and Formation Some abundant minerals: Iron and

aluminum Some rare minerals: copper, chromium,

molybdenum, etc. Abundance ≠ easy to mine Minerals are distributed unevenly rich

deposits or almost none

How do deposits form? Magmatic concentration = cooling magma

solidifies and separates into layers, heavier minerals on the bottom (iron, magnesium, etc.), lighter minerals on top (silicon)

Hydrothermal processes = groundwater that has been heated in the earth seeps into cracks and fissures and carries minerals, which settle out and form deposits

How do deposits form? Sedimentation = weathered rock

particles are carried by wind and/or water and settle out, forming deposits

Evaporation = water containing minerals evaporates away, but leaves the minerals behind salt deposits

Discovering mineral deposits Aerial or satellite photography Measuring Earth’s magnetic field and gravity Looking for typical areas in the Earth’s crust

for a particular mineral Ocean floor mapping

Once a possible location is determined, geologists drill or tunnel for mineral samples to identify

Extracting Minerals - Mining Surface mining = minerals are

extracted near the surface Subsurface mining = minerals are too

deep and need to be extracted with alternate methods

Overburden = soil, rock, vegetation, etc. that must be removed to access the mineral

Surface Mining Open-pit surface mining = giant hole is

dug quarry Strip mining = trench is dug to extract

minerals, then a new trench is dug and overburden is dumped into old one, creating a spoil bank

Subsurface mining Shaft mine = direct vertical

shaft to a vein of ore Slope mine = slanting

passage that makes it possible to haul the broken ore out of the mine in cars

Processing Minerals Smelting = melting ore at high

temperatures to help separate impurities, can be done in a blast furnace

http://www.youtube.com/watch?v=Ea_7Rnd8BTM

Words to Know… Coke = modified coal used as an

industrial fuel Slag = less dense than iron ore, floats

on the top, formed when limestone reacts with impurities in the ore

Mining and the Environment Disturbance to land prone to erosion Air pollution Water pollution

Developed nations tend to have laws and mechanisms to minimize environmental damage; developing nations either don’t have them or are still developing them

Mining and Water Digging too deep = hitting the water table

Open-pits must now be pumped dryGroundwater, springs, etc. start to run dry

Disturbed soil can runoff into water = increased turbidity, might contain dangerous chemicals or heavy metals

Thermal pollution = increasing the temperature of water so that native organisms can no longer survive

Cost-Benefit Analysis of Mine Development Environmental economists suggest that

cost-benefit analyses should be performed before developing a mine

Benefits of mine vs. benefits of keeping land intact for wildlife, habitat, watershed protection, and recreation purposes (all in $ amounts)

Should consider long term

Refining Minerals Removing waste products (tailings)

from ore, usually left behind on ground or in water near a processing plant

Smelting plants can emit large amounts of air pollution

Heavy metals (such as lead, cadmium, arsenic, and zinc) can pollute atmosphere, water, and land

Takes huge amounts of energy

Waste Production for Selected MineralsMineral Amount of Mined

Ore (Million Tons)Percentage of Ore That Becomes Waste During Refining

Iron 25,503 60

Copper 11,026 99

Gold 7,235 99.99

Zinc 1,267 99.95

Lead 1,077 97.5

Aluminum 856 70

Restoration of Mining Lands When a mine is no longer profitable to

operate, the land can be reclaimed, or restored to a seminatural conditionPrevents further degradation and erosionEliminates or neutralizes local sources of

pollutantsMakes land productive for purposes other

than miningMakes land visually attractive

Restoration of Mining Lands Derelict lands = lands that have been

degraded by mining Some restoration techniques:

Filling in and grading the land to its natural contours

Planting vegetation to hold soil in placePlants might have to be able to survive

heavy metals or without topsoil

Surface Mining Control and Reclamation Act of 1977 Reclamation of areas that are surface

mined for coal is required No requirement for non-coal mines

Creative Approaches Wetlands = trap sediments and

pollutants that enter them from upstream areas, improving the quality of water downstream

Cow manure = dumping cow manure on mining sites can cause the pH to increase as bacteria consume the manure; toxic materials precipitate out

Creative Approaches Phytoremediation = using specific

plants to absorb and accumulate toxic materials, ex. Streptanthus polygaloides (twist flower) absorbs nickel and other toxic materials

Mining and the Economy The economies of industrialized countries

require the extraction and processing of large amounts of minerals to make products

More industrialization = more minerals used Developed countries = lots of restrictions,

may have exhausted their own supplies Developing countries = economies extremely

dependent on selling minerals to developed countries, little to no restrictions

Consumption of Select Minerals

Distribution vs. Consumption

Distribution vs. Consumption Certain minerals are necessary for many

products that are vital to the economic success of a nation, but are only present in limited amounts

International trade is necessary to acquire the mineral

Some countries stockpile certain minerals (ex. Titanium, tin, manganese, chromium, platinum, and cobalt) to reduce their dependence on other countries

Will We Run Out of Important Minerals? Mineral reserves = mineral deposits that

have been identified and are currently profitable to extract

Mineral resources = deposits of low-grade ores; potential sources of minerals, but currently unprofitable supply and demand

Total resources (world reserve base) = combination of a mineral’s reserves and resources

Will We Run Out of ImportantMinerals? Reserves and resources fluctuate with

economic, technological, and political changes

Technological advances can decrease the cost of extracting ores resources can be reclassified as reserves

Political turmoil can make it so that a mineral reserve cannot be mined reclassified as resource

Will We Run Out of Important Minerals?

Increasing Our Mineral Supplies Locating and mining new deposits

may be blocked by heavy vegetation, shifting ice, too deep in the earth, etc.

New technology may allow us more access

Minerals in Antarctica No substantial deposits, only small amounts Antarctic Treaty = international agreement

(1961) that limits activity in Antarctica to peaceful uses such as scientific studies

Environmental Protection Protocol to the Antarctic Treaty (Madrid Protocol) = (1990) No mineral exploration or development for minimum of 50 years, preserves Antarctica as a marine ecosystem

Minerals from the Ocean Minerals could possibly be extracted

from seawater or where they have accumulated in loose sediments

Total amount of minerals available = high

Concentration of seawater = low

Minerals from the Ocean Manganese nodules = small rocks the

size of potatoes that contain manganese and other minerals on the ocean floor

~1.5 million tons available, but dredging them from the sea floor would hurt sea life in the area

International waters = Who has the right to these minerals?

U.N. Convention on the Law of the Sea (UNCLOS) Formed in 1982, became effective in

1994 Allows for deep seabed mining beyond

national jurisdictions US has refused to ratify it

Biomining Using microorganisms to extract

minerals from low-grade ores Very effective for copper mining Thiobacillus ferroxidans can be mixed

with sulfuric acid to leach copper into an acidic solution

Gold and phosphates can also be extracted in similar manners

Mineral Substitutes Find an inexpensive or abundant material to

replace an expensive or scarce one Plastic, glass, and aluminum have been used as

substitutes for tin Plastic has partially replaced lead and steel in

cables Glass fibers have replaced copper wiring in

telephone cables Some minerals have no known substitutes. For

example, platinum cannot be replaced as a catalyst for many reactions.

Mineral Conservation Reuse = the same product is used over

and over again, such as washing and refilling a glass bottle

Recycling = products are collected, remelted, reprocessed, etc. into new products, such as melting down metal cans and making new ones

Changing Our Mineral Requirements Stop the “throwaway” mentality repair

or repurpose Waste from one industrial process can

be used as raw materials in another economic and environmental benefits

Sustainable manufacturing = reducing waste by more efficient manufacturing processes or converting the waste into useful products

Dematerialization Decreasing weight

and/or mass of materials needed in a product

Can have negative effects flimsier products can break more easily and be cheaper to replace than to repair

In Conclusion… Soil and minerals are both important

limited resources Both can be permanently damaged or

used up Both can be protected AND enjoyed by

sustainable use and development

Vids http://www.pbs.org/wgbh/nova/education

/earth/rare-earth-elements.html Rare earth minerals

http://www.youtube.com/watch?v=Ego6LI-IjbY Soil Stories – The Whole Story

http://www.youtube.com/watch?v=pVoXW4YrqTs Surviving the dust bowl

http://www.teara.govt.nz/en/soil-erosion-and-conservation/3 Types of erosion