Soils and the Environment

Learning Objectives

• Soils terminology & processes• Interaction of water in soil processes, soil

fertility• Classification of soils (familiarity)• Engineering properties of soil• Relationships between land use and soils• Sediment pollution• Desertification

• How/why is soil important in environmental geology? 

• What is soil? Definition(s)?

• How does soil form?

• How does chemical weathering work?

• What is the significance of mechanical weathering?

• Factors/parameters that affect soil formation?

• What is a “soil profile”?

• What are soil horizons? Types?

• What effect(s) does climate have on soil formation? Examples?

• What are the three main types of soil properties?

• What is the significance of “categorizing” soils by these properties?

• How are soils identified by texture?

• How are soils identified by structure?

• What other types of soil properties are there? Explain

 

• How/where do soils fit into natural cycles/systems

– in terms of interactions with atmosphere, hydrosphere, etc.?

– in terms of e.g., the nitrogen cycle?

 

• How are soils classified? Significance?

• Distribution/examples of soil classification?

• What are soil phases?

• What are the “engineering properties” of soil? Significance?

• What is the soil/erosion loss equation? How used? Significance?

• What is sediment pollution?

• How do human activities affect soils?

• What are the main problems associated with soils?

• How do the following affect soils?

• - Urbanization

• - Off-road vehicles

• - Land use

• - Soil pollution

• What is desertification? What are the driving forces? Explain

• What factors affect desertification?

• Where do deserts occur? Where is desertification occurring? Significance?

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• What is the significance of swelling/shrinking of soils?

• What is the significance of acid mine drainage on soil?

• What are soil surveys? Explain

• What are some types/examples of corrective measure used to address problems

associated with soils?

The word "soil" means different things to different people

• Farmers: – That part of the earth's surface

contained decayed and organic material in sufficient quantity to grow plants and crops.

• Geological: – Unconsolidated, unlithified residual

(left over) material from underlying parent rock which supports root growth

• Soil Science:– Altered solid earth material that can

support rooted plant life

• Engineering:– Solid earth material that can be

moved without blasting

Roles of Soils in the Environment

• Land use planning (suitability)– Soil erosion– Agriculture– Construction

• Waste management (interactions between waste, soil, water)

• Natural hazards: land use planning in terms of:– Floods– Landslides, slope stability– Earthquakes

Soil Formation• Soil formation begins with weathering• Weathering: Physical and/or chemical breakdown

of rocks (open system):– Physical (mechanical) Processes: Big ones to little ones

• Abrasion• thermal (expansion/contraction)• frost wedging

– Chemical Processes: Dissolution & alteration (congruent vs. incongruent dissolution w/residue)

• Soil Formation depends on:– Climate– Topography– Parent material– Time/age of soil– Organic processes

Physical Weathering• Making big pieces into smaller pieces

– increases surface area available for chemical weathering

Chemical Weathering• Alteration (e.g, feldspar to clay+quartz)

• Dissolution

Chemical Weathering Reactions

Soil Profile Development

Variables:– Parent material – Climate– Topography– Time (Soil age / extent

of development)– Organic activity

Soil Horizons

Climatic Effects on Soil Formation

Soil Properties/Indicators

• Color– Dark: indicative of organic material (O, A horizons) or

iron– Light:

• Whitish: Indicative of leaching (E-horizon)– Extensive leaching of iron, Al– Presence of carbonates

• Yellow, brown, red (B-horizon)

– Be careful (e.g., basaltic material, volc. ash)

• Texture (particle size)• Structure

Soil Texture (particle size)

Soil Texture: –Depends on relative proportions of sand-, silt, -clay sized particles

Soil Structure• Aggregates of soil particles = peds• Peds classified by shape (structure)

Other Soil Features/Characteristics

• Relative profile development– Weakly developed

– Moderately developed

– Well developed

• Soil Chronosequences– Arrangement from youngest to oldest

– Significance? When needed or used? (see fig.)

– How determined (if not obvious)?

More Soil Features/Characteristics

• Soil Fertility– Definition: Capacity of soils to supply nutrients

(N, P, K)– Significance?

• Water in Soils– Soil moisture

• Saturated• Unsaturated

– Significance?

Cycles / Systems Associated With

Soils

Soil Classification

• Soil Taxonomy– (See Table)

• Engineering Classification– (See Table)

Engineering Properties of Soils

• Soil phases1. Solid material

2. Liquid

3. Gas

• Soil Properties– Placsticity– Soil strength– Cohesion– Friction– Sensitivity– Compressibility– Erodibility– Permeability– Corrosion– Ease of excavation– Shrink-swell potential

Soil Erosion/Loss

• Loss of volume, mass, or weight of soil from a location in a specified time and area e.g., kg/yr/hectare

• Universal Soil Loss EquationA = RKLSCP

• Significance (of factors & result)?

A = long-term avg. annual soil loss for the site

R = long-term rainfall runoff erosion

K = Soil erodibility index

L = Hillslope/length factor

S = Hillslope/gradient factor

C = Soil cover factor

P = Erosion-control practice factor

Sediment Pollution:Sediment (eroded soil) as a pollutant

How is soil pollution a negative resource?

– Depletes useable soil– Reduces quality of water it enters– Deposition of sterile materials

Control/Reduction: Techniques, Examples (see text)

Figure

Land Use & Other Soil Problems

• Human activities affect soils by influencing patterns, amounts, and intensity of:– Surface-water runoff– Erosion– Sedimentation– Conversion/manipulation of natural areas &

surface water(see Figures 3.12, 3.13)

Soil Erosion due to diversion of runoff water

Land Use & Other Soil Problems

• Urbanization

• Off-Road Vehicles

• Soil Pollution

• Desertification

• Others

Effects of land use on sediment yield; with sharp peak during construction & urbanization

Off-road vehicle excavation

Urbanization erosion

Land Use & Other Soil Problems

• Urbanization

• Off-Road Vehicles

• Soil Pollution

• Desertification

• Others

Land Use & Other Soil Problems• Urbanization• Off-Road Vehicles• Soil Pollution• Desertification

Driving Forces:

• Overgrazing

• Deforestation

• Soil erosion

• Poor irrigation drainage

• Overdraft of water supplies

• Off-road vehicle erosion

Desertification Factors:•Declining water table

•Salinization of soil & near-surface water

•Enhanced soil erosion (wind and/or water)

•Damage to native vegetation

Extent of desertification of arid lands of the world

Land Use & Other Soil Problems

• Urbanization

• Off-Road Vehicles

• Soil Pollution

• Desertification

• Others– Swelling & shrinking– Acid mine waters

Swelling & Shrinking of Soil Minerals

Soil Surveys & Land Use Planning

• Descriptions

• Soil Maps (types, extent, properties)

• Information for identifying potential problems/issues BEFORE use (e.g., construction)

Corrective Measures

• Erosion Controls– Terracing, contour stripping– Vegetation barriers– Water/sediment basins/reservoirs– Characterization & planning

• Pollution abatement– Treament, e.g., bioremediation

• Others?

Storm water sediment basin

Summary/Overview• Definitions of soil• Roles of soils in

environmental geology– Land use planning

– Waste disposal

– Evaluation of natural hazards

• Formed from rock interactions in the hydrologic cycle (explain)

• Variables (explain)– Climate– Topography– Parent material– Time– Organic activity

• Soil processes form distinctive layers (horizons)

• Soil Properties:– Color– Texture (particle size)– Structure (peds)

Learning Objectives

• Soils terminology & processes• Interaction of water in soil processes, soil fertility• Classification of soils (familiarity)• Engineering properties of soil• Relationships between land use and soils• Sediment pollution• Desertification