Environmental Science Ii: Soils

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Soils

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1. Earth material that has been altered by physical, chemical, and biological processes such that it can support rooted plant life.

2. Engineers define soils as anything that can be removed without blasting.

3. Soils form from the in situ weathering of rock or regolith at the earth’s surface and are composed of mineral matter, organic matter, and pore space (which may contain air and or water).

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Soil Properties & Environmental Investigations

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1. Soils can be used in land-use planning for suitability studies

2. Soils are critical in waste-disposal (solid and liquid) problems

3. Soils can aid land-use planners evaluate natural hazards such as flooding, landslides, and earthquakes.

4. Soils carry climatic signals, indicating that past climate and possible climate changes.

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Residual Soils

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Soils formed from the residue of in Place Rock materials

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Transported Soils

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Soils formed from sediment materials transported into place by the agents of erosion or by mass wasting.

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Soil Profile Development

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1. Soils form from the surface downwards

2. The oldest soil is nearest the surface, the younger soil is recently formed from the parent material.

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New Soil

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Organic material at the surface (O-Horizon), with a poorly formed C- and D-Horizons.

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Intermediate Stage

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O-,B-,C- and D-Horizons

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Mature Soil Profile

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Full complement of soil horizons, each of which will thicken as the process of soil formation continues downwards.

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O-Horizon

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1. Organic horizon

2. Dead and decaying plant and animal matter

3. Humus

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A-Horizon

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1. Zone of leaching

2. Oldest Soil

3. Most modified (differing the most from the parent material)

4. This may also contain the E-Horizon (hard pan, or layer containing evaporate deposits.)

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B-Horizon

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1. Zone of Accumulation

2. Enriched in materials leached from the upper layers

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C-Horizon

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1. Partially decomposed parent material

2. Mostly mechanical weathering, with slight chemical weathering

3. Most like the parent material

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D R-Horizon

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1. Parent material

2. May be bedrock or sediment

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Alfisols

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1. Moderately leached forest soils that have relatively high native fertility.

2. These soils are well developed and contain a subsurface horizon in which clays have accumulated.

3. Alfisols are mostly found in temperate humid and subhumid regions of the world

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Andisols

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1. Soils that have formed in volcanic ash and other volcanic ejecta.

2. These soils differ from those of other suborders in that they are typically dominated by glass and poorly crystalline colloidal materials.
3. Possess many unique chemical and physical properties including high water-holding capacity and the ability to fix large quantities of phosphorous.

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Aridisols

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1. Are calcite-containing soils of arid regions that exhibit at least some subsurface horizon development.

2. They are characterized by being dry most of the year

3. They contain subsurface horizons in which clays, calcium carbonate, silica salts, and or gypsum have accumulated.

4. They are used mainly for range, wildlife, and recreation.

5. Because of the dry climate in which they are found, they are not used for agricultural production unless irrigation water is available

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Entisols

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1. Soils of recent origin
2. The central concept is soils developed in unconsolidated parent material with usually no genetic horizons except an A-Horizon.

3. All soils that do not belong in any of the other orders belong here.

4. They are characterized by great diversity, both in environmental setting and land use.

5. Many are found in steep, rocky settings; however, Entisols of large river valleys provide eroplands and habitat for millions of people of the world.

6. Most extensive soil order, occupying 16.2% of the world’s ice-free land area

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Gelisols

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1. Soils of very cold climates that contain permafrost within 2 meters of the surface

2. These soils are limited geographically to high-latitude polar regions and high mountain elevations.

3. Low soil temperatures cause soil-forming processes such as decomposition of organic materials to proceed very slowly

4. Gelisols store large quantities of organic carbon

5. They surpass swamps and marsh ecosystems

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Inceptisols

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1. Soils that exhibit minimal horizon development

2.They are more developed than Entisols, but still lack the features that are characteristic of other soil orders.

3. Inceptisols are widely distributed and occur under a wide range of ecological settings

4. They are often found on fairly steep slopes, young geomorphic surfaces, and on resistant parent materials

5. Many are found in mountainous areas and are used for forestry, recreation, and watersheds

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Molisols

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1. Soils of grassland ecosystems

2. They are characterized by a thick, dark surface horizon

3. Fertile surface horizon results from the long-term addition of organic materials derived from plant roots

4. Occur primarily in prairie regions, such as the Great Plains of the US

5. Molisols are among some of the most important and productive agricultural soils in the world and are extensively used for this purpose

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Oxisols

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1. Very highly weathered soils that are found primarily in intertropical regions of the world

2. These soils contain few weatherable minerals and are often rich in iron and aluminum oxide minerals

3. These soils are characterized by extremely low native fertility, resulting from very low nutrient reserves and high phosphorous retention by oxide minerals, and low cation exchange capacity

4. Most nutrients in oxisol ecosystems are contained in the standing vegetation and decomposing plant material

5. Despite low fertility, Oxisols can be quite productive with inputs of lime and fertilizers

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Spodosols

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1. Acid soils characterized by a subsurface accumulation of humus that is complexed with aluminum and iron

2. These photogenic soils typically form in coarse-textured parent material that have light-colored E-Horizon overlying a reddish-brown spodic horizon

3. Spodosols often occur under coniferous forests in cool, moist climates

4. Many support forests, but because they are naturally infertile, they require additions of lime in order to be productive agriculturally

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Ultisols

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1. Strongly leached, acid forest soils with relatively low native fertility

2. They are found primarily in humid temperate and tropical areas of the world, typically in older, stable landscapes

3. Intense weathering of primary minerals has occurred and much of the Ca, Mg, and Khas have been leached from these soils

4. Ultisols have a subsurface horizon in which clays have accumulated from the presence of iron oxides, because of favorable climate regimes in which they are typically found
o Ultisols often support productive forests

5. Because of their acidity and relatively low quantities of plant available Ca, Mg, and K, Ultisols are poorly suited for agriculture without the use of fertilizer and lime

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Vertisols

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1. Clay-rich soils that shrink and swell with changes in moisture content

2. During dry periods, the soil volume shrinks and deep wide cracks form.

3. The soil volume expands as it gets wet

4. The shrink/swell action creates serious engineering problems and generally prevents the formation of distinct well-developed horizons

5. Vertisols occupy 2% of the US land area and occur primarily in TX

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Soil Properties

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1. Color

2. Texture

3. Structure

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Color

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1. Soil color can indicate the degree and type of weathering of the soil

2. Soil color may be an indicator of how well a soil drains:

3. Well-drained soils are well aerated, creating oxidizing conditions with red colors (unless aluminum, then white)

4. Poorly-drained soils are wet, and tend to be yellowish (or dark, reduced iron)

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Histosols

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1. Soils that have a lot of tissue material and are dark in color

2. Much lighter in weight

3. They form in settings where there is restricted drainage

4. They are mined for fuel and horticultural products

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Texture

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1. Relative percentage of sand, silt, and clay

2. Sand is good for drainage and oxygen getting to the roots, but if too much sand they are overly drained and tend to be dry

3. Clay is good for water retention cation exchange but hard to get water or oxygen into the soil

4. Silt is intermediate between the other two

5. Loam is a mixture of sand, silt and clay which has the best characteristics of the three combined

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Structure

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1. Soil particles
Peds

2. Types
•Granular
•Blocky
•Prismatic
•platy

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Soil Fertility

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1. refers to the capacity of the soils to supply nutrients, such as nitrogen, phosphorous, and potassium, needed for plant growth

2. soils that develop on some floodplains and glacial deposits contain sufficient nutrients and organic materials to be considered naturally fertile

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Soil Water

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1. Soils are composed of mineral matter, organic matter, and pore space

2. The pore space can contain water and/or air.

3. Too much water drowns the plants, because they need both water and oxygen from the soil

4. The amount and movement of water through the soil are important research topics, both are linked to numerous water pollution problems, such as the movement of gasoline from leaking underground tanks or the migration of liquid pollutants from waste-disposal sites

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Engineering Properties of Soils

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1. The composition of the soils determines the property of the soil.

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Soil Strength

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1. Ability of a soil to resist deformation

2. Soil strength can vary over a relatively small area.

3. The composition of the clay content (type), as well as water in the pores can affect the soil strength.

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Soil Sensitivity

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1. Measures the changes in soil strength resulting from disturbances such as vibrations or excavation
2. Sand and gravel soils with no clay are the least sensitive

3. Clay soils become more and more sensitive and may lose 75% or more of their strength after a disturbance

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Soil Compressibility

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1. Measure of a soil’s tendency to consolidate, or decrease in volume

2. Compressibility is partially a function of the elastic nature of the soil particles and is directly related to the settling of structures, such as the Leaning Tower of Pisa.

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Erodibility

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1. The ease with which soil materials can be removed by wind or water

2. Cohesive soils, which are more than 20% clay, and naturally cemented soils, or coarse gravel-rich soils are not easily eroded by wind or water and therefore have a low erosion factor

3. Soils with a high erosion factor include unprotected silts and sands

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Hydraulic Conductivity

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1. Measure of the ease with which water moves through a material

2. Measured in units of velocity

3. Clays have low hydraulic conductivities, making them good sealing layers for waste disposal and lining of lagoons

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Corrosion Potential

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1. Is a slow weathering or chemical decomposition that proceeds from the surface into the ground.

2. Objects buried in the ground-pipes, cable anchors, and fence posts are all subject to corrosion

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Ease of Excavation

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Refers to the procedure required to remove the soil material

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Categories of Excavation

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1. Common excavation
earth mover, backhoe, or bulldozer

2. Rippable excavation
requires breaking up the soil with special ripping teeth before it can be removed

3. Blasting or rock cutting
a hard silica cemented soil might need to be cut with a jackhammer before being removed

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Shrink-Swell Potential

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1. The tendency of a soil to gain or lose volume as it gains water

2. Can depend upon the type of clay mineral in the soil, such as Montmorillonite.

3. Ex. Mudcracks, driveways, cracks in foundation

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Rates of Soil Erosion

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1. Soil erosion is the worst where erosion exceeds the rate of formation

2. In some places in the US, poor farming practices have resulted in the loss of feet of soil in less than 200 years

3. Construction is bad too, soil in the street after rain, eroded soil goes into waterways, which turns into soil pollution

4. The average rate of soil formation is 1 cm every 1000 years

5. Once the soil is lost, it must be reformed before an ecosystem can establish itself again.

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Sediment Pollution

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1. Soil erosion can result in particulate pollution (sediment)

2. Rivers commonly carry sedimentary particles from the general patterns of erosion. Even in desert areas, water is the dominant agent of transportation of sediments

3. When human activities accelerate the rate of erosion, sediment can become a problem in waterways

4. Sediment pollution can reduce oxygen (reduce photosynthesis), increase water temperatures (by absorption of radiation by the particles), and drive out oxygen, clog the gills of fish, and fowl surfaces.

5. Sediment pollution in cities can choke the drainage pipes, increasing flooding

6. Sediment pollution can infill reservoirs

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Land Use & Environmental Problems of Soils

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1. Human activities affect soils by influencing the pattern amount, and intensity, of surface water runoff, erosion, and sedimentation

2. Changes in land use can increase problems related to the use of soils

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Agriculture

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1. Soil erosion and the overuse of soils by intensive agriculture have damaged about 10% of the world’s agricultural lands

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Alternative plowing practices

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1. Contour plowing
plowing with the natural topography of the land

2. No-till agriculture
eliminate plowing to reduce soil erosion

3. Terracing slopes
production of flat surfaces

4. Intercropping
a. Alternate ground crops with row crops
b. Row crops protect from the wind, while cover crops protect from water erosion
c. Hedge rows around fields to protect from winds

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Urbanization

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1. Soils may be scrapped off and lost

2. Materials may be brought in from the outside to cover the native soil

3. Draining soils to remove water may result in a change in the chemistry of the soil and changes in its behavior

4. Soils in urban areas are more susceptible to pollution from deliberate and inadvertent contamination from fertilizers, pesticides and herbicides, and household chemicals.

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Off-Road Vehicles

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1. Stripping vegetation

2. Compacting the ground

3. Mountain bikes and the trails along the buffalo bayou, as an example

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Soil Surveys & Land-Use planning

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1. The soil Conservation service (which was the soil service, and is now the US natural resource conservation service), after the Dust Bowl of the 1930’s was charged to determined the soil characteristics of the US.

2. One of their jobs was to establish soil surveys for all the counties of the US

3. An individual soil survey of a property is needed to ensure proper engineering practices and property uses.

4. Greentree Reservoir and the need for soil studies.