Chapter 1 Environmental Science: Studying the State of Our...

Ch 8Earth SystemsModules 25Weathering and Soil Science

11/13/17

Weathering vs. Erosion

• Weathering – Breakdown of rocks

• Erosion – Moving of broken-down

material

Weathering

• Physical weathering The mechanical breakdown of rocks and minerals.

o Water

o Frost Wedging

o Roots

o Animals

Weathering• Chemical weathering The breakdown of

rocks and minerals by chemical reactions, the dissolving of chemical elements from rocks, or both.

o Oxidation (rust)

o Acids

o Water

Soil Formation

Five factors determine the properties of soil:

• Parent material (rock material from which the inorganic components of a soil are derived)

• Climate

• Topography

• Organisms

• Time

Organics

Topsoil

Subsoil

Parent Rock

Caliche

• Generally in arid or semiarid regions in aridisol soil

• Hardened natural cement of calcium carbonate that binds gravel, sand, clay, and silt

• Forms when minerals leach from the upper layer of the soil (the A horizon) and accumulate in the next layer (the B horizon)

• Occurs at depths of approximately 3 to 10 feet under the surface

Properties of Soil

Particle Size

Properties of Soil

Permeability

• The permeability of soil depends on its texture.•Sand, with its large, loosely packed particles, drains quickly.

•Clay drains much more slowly.

Permeability

Texture

• Important for Cation Exchange Capacity

• Clay has (-) charge

• Soils with high CEC desirable to agriculture

• 20%+ clay, too much water retention

Soil Conservation

Erosion

Compaction

Salinization

Soil is a nonrenewable resource

Entisols

• Little to no soil development

• Occur in areas of recently deposited sediments

• Entisols make up the second largest group of soils, occupying about 16% of the Earth’s surface

Aridisols

• The climate in which Aridisols occur also restricts soil weathering processes

• Often contain accumulations of salt, gypsum, or carbonates, and are found in hot and cold deserts worldwide

• Occupy about 12% of the Earth’s glacier-free land area

• Majority of soil around the Phoenix metro area