soils exam 4

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  1. Soil erosion
    the wearing away of the land surface by water, wind, or other natural or anthropogenic agents that detach the soil from one point on the earth's surface and deposit it elsewhere
  2. Steps of soil erosion
    • Detachment 
    • Transportation of sediments
    • Deposition
  3. Onsite effects of soil erosion
    • loss of fertile topsoil 
    • exposure of unproductive subsoil
  4. Off-site Effects
    • siltation of damns, lakes, river, etc.
    • water pollution
  5. Two Types of Erosion
    • Natural: erosion under natural environmental conditions
    • Accelerated: erosion that is much more rapid than usual
  6. Types of Water Erosion
    • Splash
    • Sheet
    • Rill
    • Gully
    • Steam erosion
  7. Splash Erosion
    • the particles are detached by the force of falling raindrops
    • soil rises into the air and maybe moved by gravity or wind or water down-slope
  8. Sheet Erosion
    soil particles are detached and transported in a thin layer or sheet by water flowing on surface
  9. Rill/Gully Erosion
    rills and gullies (gullies being larger) can be cut as runoff is allowed to concentrate and gain velocity
  10. Stream Erosion
    erosion that occurs along the banks of streams; cuts away at banks
  11. Factors Controlling Erosion
    • Surface Cover (vegetation) 
    • Topography
    • Soil Properties (texture, structure, aggregate formation, etc.)
    • Climate Factors
  12. 7 cultural measures of controlling soil erosion
    • conservation tillage
    • cover cropping
    • mulching 
    • proper timing of cultivation
    • addition of soil conditioners (organic matter, lime)
    • contour cultivation
    • strip cropping
  13. Conservation tillage methods
    • no-till
    • reduced till
    • ridge till
    • strip till
    • mulch till
  14. Mechanical/Engineering measures
    • Riprap
    • Terracing
    • Bioengineering
    • Sediment traps
    • Retention Ponds
  15. Riprap
    • Large angular rocks may be laid at the bottom or side of channels where high water velocities may be expected
    • stream bank erosion can account for 40% or more of total soil loss in some watersheds.
  16. Terracing
    not very common in the US because we have cultivated lands that are relatively flat.
  17. Bioengineering
    use of vegetaion to protect channels, reduce runoff velocity, and trap sediments
  18. Sediment traps
    designed to slow down runoff and trap sediments
  19. Retention Ponds/Sedimentation Basins
    ponds constructed down-slope of field which collects runoff and allows sediments to settle prior to movement of surface water off-site
  20. Why estimate soil loss?
    • To plan for the best management of a soil resource
    • to evaluate the consequences of alternative tillage practices/shift in management strategy 
    • To determine compliance of environmental regulations
  21. Models used to estimate soil loss- WEPP
    • WEPP: Water Erosion Precition Project.  
    • Predicts how rainfall will impact a site
    • can predict on-site and off-site effects
  22. Models used to estimate soil loss- USLE
    • USLE: Universal Soil Loss Equation (now revised) 
    • relies on statistical relations between easily observed factors to soil erosion (rainfall erosivity, soil erodibility, etc)
    • Advantage: can show management strategies can affect erosion
    • cannot predict erosion for a specific year (only average year) or storm
    • sheet and rill erosion
  23. Wind Erosion in the US- key facts
    • Wind moves 40% of the soil transported by erosion in the U.S.
    • Problem in 75 million acres of land in the U.S.
    • Up to 29 Mg/ha of wind erosion-induced losses had been recorded in New Mexico
  24. Three factors affecting wind erosion
    • wind velocity and turbulence 
    • surface roughness
    • soil properties
  25. Threshold velocity required for wind erosion
    25 km/hr, 15 mi/hr
  26. 3 modes of wind-induced transportation
    • Saltation (50-90% of soil movement)
    • Suspension (less than 15% of total movement)
    • Creep
  27. Negative impacts of wind erosion
    • removes the most fertile portion of the soil
    • obscures visibility and pollutes the air and water
    • causes automobile accidents and fouls machinery 
    • imperils animal and human health
  28. Wind Erosion Control Strategies
    • Maintain or increase the protective cover of plants
    • conservation tillage to maintain aggregate stability and reduce disturbance- especially in arid areas
    • installation of barriers/wind breaks (aka wind barriers, shelterbelts)
    • keep surface layer moist and rough
  29. Marginal soil characteristics
    • Infertile 
    • Low in organic matter
    • often acidic
    • subject to severe erosion and surface run-off
  30. Rehabilitating Marginal Soils
    • control soil erosion: use fast-growing perennial vegetation 
    • enrich soil organic matter: increases fertility and improves soil physical properties 
    • correct soil pH
    • conservation tillage 
    • plant cash crops that cover the soil and employ crop rotation
    • apply fertilizers
  31. Acid-sulfate soils
    soils that are potentially extremely acidic (<3.5) because of the presence of large amounts of reduced form of sulfate that are oxidized to sulfuric acid if the soil is exposed to oxygen when they are drained or excavated.
  33. How can we enhance soil sequestration of carbon?
    • Continuous supply of organic residues (increase decomp rate)
    • keep the soil vegetated 
    • maintain soil fertility
    • tillage should be eliminated or limited
    • perennial vegetation (especially in natural ecosystems) should be encouraged
  34. Landfills
    natural attenuation
  35. Products of treatment plant
    • Sewage effluent: released into rivers/creeks OR applied as irrigation to crops OR surface-applied to drain-fields 
    • Sludge: surface-applied to agricultural areas
  36. Excess nutrients- Nitrogen and Phosphorus
    • manure application rates based on N (P may be over applied inadvertently)
    • Farmer apply extra to apply "enough"
    • N and P may come from septic and domestic waste
  37. Sources of pathogenic bacteria
    • farm wastes (liquid wastewater and manure) 
    • faculty septic systems
    • domestic animals, stray animals and migratory birds
    • contaminated irrigation and groundwater to wash produce
  38. Soils properties which help in treating bacteria
    • high specific surface (lots of clay)
    • Red soils- high iron content bacteria sorbs into/forms complexes with iron oxides
    • well-drained soil/unsaturated soils (most pathogens are facultative anaerobes and will be out competed by aerobic microbes in oxygen-rich environments)
  39. Heavy metal sources
    • mining
    • manufacturing
    • the use of synthetic products
  40. Effects to humans
    • toxicity due to extended exposure (due to food chain transfer)
    • some metals carcinogens
    • acute poising through ingestion (rare)
  41. If you have cationic heavy metals in the soil...
    you lower the pH
  42. Manipulating draining for heavy metals
    • if chromium, add organic matter
    • if other heavy metals, drain soils for greater oxygen availability (creates oxides which are less soluble)
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soils exam 4
soils exam 4
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