Soil and Environment.Geo 305
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- 3. Introduction • Regolith is a layer of loose, heterogeneous superficial material covering solid rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, Mars, some asteroids, and other terrestrial planets and moons. • Soil scientists define soil as upper layers of regolith that support plant growth. • Engineering geologists define soil very broadly to include all unconsolidated material overlying bedrock. 3
- 4. Why soil is Important to Humans? • Soil and land use planning • Land capability for urbanization, timber management, and agriculture • Soil and waste disposal • Soil and natural hazards • Soil and climatic signals 4
- 5. Formation of Soil • Soil is produced by weathering, a term that encompasses a variety of chemical, physical, and biological processes acting to break down rocks and minerals. • Residual soil and transported soil. • Soil characteristics are function of climate, topography, parent material, Time and biological processes. 5
- 6. Some essential Terminologies • Eluviation - The process of washing down material such as organic matter or minerals through the soil. • Illuviation - The deposition in a soil horizon of minerals, humus and other materials. • Leaching - The dissolving and washing down of calcium and other bases through the soil as a result of percolating rain water. Bases are substances which react with an acid to form a salt and water. Some bases dissolve in water and are then called alkalis e.g. the hydroxides of sodium, calcium and potassium. 6
- 7. 7 Approximate composition of Soil Soil Aeration Saturated vs Unsaturated Soils
- 8. Soil Profile and Soil Horizons • Vertical and horizontal movements of the materials in a soil system create a distinct layering, parallel to the surface, collectively called a soil profile. The layers are called zones, or soil horizons. 8
- 9. 9 O. Horizon is composed mostly of organic materials including decomposed or decomposing leaves, twigs, etc. The color of the horizon is often dark brown or black. A. Horizon is composed of both mineral and organic materials. The color is often light black to brown. Leaching, defined as the process of dissolving, washing, or draining Earth materials by percolation of groundwater or other liquids, occurs in the A horizon and moves clay and other material such as iron and calcium to the B horizon. E. Horizon is composed of light-colored materials resulting from leaching of clay, calcium, magnesium, and iron to lower horizons. The A and E horizons together constitute the zone of leaching. B. Horizon is enriched in clay, iron oxides, silica, carbonate, or other material leached from overlying horizons. Horizon is known as the zone of accumulation. C. Horizon is composed of partially altered (weathered) parent material; rock is shown here but the material could also be alluvial in nature, such as river gravels in other environments. The horizon may be stained red with iron oxides. R. Unweathered (unaltered) parent material. Soil Horizons
- 10. 10 Soil Types Pedalfer Pedocal Laterite Under forest Vegetation Drier Grasslands Hot, wet tropical Climates Iron Oxide and Aluminum-rich clays in the B-Horizon Calcium Carbonate Intense chemical weathering to the top layer of soil
- 11. Soil Properties • Color Depending on the amount of organic matter, consituents minerals, aeration or aerification, soil drainage. • Texture Relative proportions of sand, silt, and clay-sized particles, affect soil’s strength and ability to retain water and nutrients. • Structure Aggregates of soil as peds. The more developed with time, the more complex a soil’s structure, from granular to blocky to prismatic. 11
- 12. 12 Figure 12.6 (Environmental Geology by C.W. Montegomery) Soil-texture terminology reflects particle size, not mineralogy. Diagram simplified from U.S. Department of Agriculture classification scheme.
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- 14. • A weakly developed soil profile: A horizon directly over a C horizon (no B horizon or it is very weakly developed), relatively young few hundreds to a few thousands years old. • A moderately developed soil profile: A horizon overlying an argillic Bt horizon that overlies the C horizon, from at least the Pleistocene (more than 10,000 years old). • A well-developed soil profile: Redder colors in the Bt horizon, more translocation of clay to the Bt horizon, and stronger structure, may have K horizon; older than 40,000 years. Relative Soil Profile Development and Chronosequence 14
- 15. Soil Fertility • Soil’s capability to supply nutrients needed for plant growth, such as N, P, K • Fertility changes • Increase: Applying fertilizers or mixing materials to improve soil texture • Decrease: Leaching or soil erosion 15
- 16. Water in Soil • Soil pores are filled with air or liquid • Saturated and Unsaturated Soils • Saturation level: changes with climate and seasons (hardly saturated in arid climate) • Movement of water: Important in pollution monitoring and management 16
- 17. Engineering properties of soil • Soil strength is its ability to resist deformation, function of cohesive and frictional forces between particles. • Soil sensitivity is measure of changes in soil strength from disturbances. • Soil compressibility is its tendency to consolidate or decrease in volume. • Soil erodibility is the ease with which soil is removed by wind or water • Soil hydraulic conductivity is the ease with which water moves through a material. • Soil corrosion potential is slow weathering or chemical decomposition that proceeds from the surface into the ground. • Shrink-well potential is the tendency of a soil to gain or lose water. • Ease of excavation the degree of ease to remove soil using certain equipment during construction 17
- 18. Rates of Soil Erosion • Volume, mass, or weight of soil removed from a specific area during a specific period of time, kilograms per year per hectare. • Types of soil erosion; splash erosion, sheet erosion, rill erosion and gully erosion. • Factors affecting erosion rates; Physical and chemical properties of soil, land use, climate, topography, tectonics. • Various approaches for measuring soil erosion. 18
- 19. The Universal Soil Loss Equation The Universal Soil Loss Equation is 𝑨 = 𝑹𝑬𝑳𝑺𝑪𝑷 where • A = long-term average annual soil loss for the site being considered • R = long-term rainfall runoff erosion factor • E = soil erodibility index • L = hillslope/length factor • S = hillslope/gradient, or slope factor • C = soil cover factor • P = erosion-control practice factor 19
- 20. Sediment Pollution • Sediments - one of the greatest pollutant. • Choking the waterways, burying vegetation, causing dust storm. • Adverse impact on water and air quality land quality, productivity using dust storms. • Preventive measures • tailoring development to the natural topography, • exposing a minimal amount of land, • providing protection for exposed soil, • minimizing surface runoff from critical areas • and trapping eroded sediment on construction sites 20
- 21. Land-use and Soil Problems • Influencing the pattern, amount and intensity of surface-water runoff, erosion and sedimentation. • Agriculture: Estimated 10 percent of the world best agricultural land damaged due to soil erosion and overuse of soil during the last 50 years • Better practice to sustain soils • Contour plowing • No-till agriculture (no plowing) • Terracing slopes, retaining walls for steep slopes • Planting more than one crop, particularly in tropical areas 21
- 22. • The conversion of agricultural, forested, or rural land to highly urbanized land causes dramatic changes. • The process of urbanization directly affects soils in several ways: • Soil may be scraped off and lost. Once sensitive soils are disturbed, they may have lower strengths when they are remolded. • Materials may be brought in from outside areas to fill a depression before construction, resulting in a much different soil than was previously there. • Draining soils to remove water may cause desiccation, or drying out, and other changes in soil properties. • Soils in urban areas are susceptible to soil pollution resulting from deliberate or inadvertent addition of chemicals to soils. This problem is particularly serious if hazardous chemicals have been applied. 22 Land-use and Soil Problems
- 23. Soil Pollution • Soil pollution: By any materials detrimental to human and other living organisms, such as organic chemicals, inorganic chemicals, toxic substances • Intentionally or accidentally applied to soils • Inappropriate disposal of waste materials • Treatment: excavation, disposal, incineration, and bioremediation 23