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Urban soil

Urban Soil
Saad Farooqi

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Urban soil

  1. 1. URBAN SOIL P R E S E N T E D B Y : S A A D F A R O O Q I , C # 0 1 B S S E M E S T E R : 6 T H D E P A R T M E N T O F E N V I R O N M E N TA L & C O N S E R V AT I O N S C I E N C E S U N I V E R S I T Y O F S W AT 2/1/2016 1
  2. 2. URBAN SOIL • Urban soils created by process of urbanization. • Highly disturbed land soil. • Human activities modified natural landscape. • Urbanization also contributes unique amendments and contaminants to the urban soil. • Bockheim (1974) gives an appropriate and useful definition of urban soil: • “A soil material having a non-agricultural, man-made surface layer more than 50 cm thick, that has been produced by mixing, filling, or by contamination of land surfaces in urban and suburban areas.” 2
  3. 3. CHARACTERISTICS OF URBAN SOIL • Vertical and spatial variability • Modified structure (compaction) • Surface crust on bare soil (hydrophobic) • Presence of anthropogenic materials, contaminants • Modified temperature regimes • Elevated pH • Restricted aeration and drainage • Interrupted nutrient cycling • Modified biological community 3
  4. 4. VERTICAL AND SPATIAL VARIABILITY • Changes abruptly at one or more levels in the profile (lithologic discontinuity) due to stripping, filling, mixing, etc. • Cumulative effects of historical uses: agriculture, roadways, buildings, utility lines, digging, filling, leveling, organic additions. • Backfilled topsoil often from another site. 4
  5. 5. Potential Lithological discontinuity 5
  6. 6. 6
  7. 7. STRUCTURE AND COMPACTION • Natural processes tend toward aggregation and lower bulk density • Soil manipulation breaks aggregates apart and increases bulk density • Disrupted organic matter cycle  poor structure and low biological activity • Disrupted freeze-thaw cycles • High salt content encourages dispersion • Little vegetative cover  bare soil  erosion • Anthropogenic compaction 7
  8. 8. SURFACE CRUSTING • Deposition of petroleum-based aerosols and particulates  water-repellant compounds • Bare soil  exposure to raindrops  disintegration of surface aggregates • Reduced infiltration and gas exchange 8
  9. 9.  AERATION AND DRAINAGE • Disrupted continuity (walls, sidewalks, curbs, pipe shafts, streets, foundations, grade changes)  damming, ponding • Impermeable covers (asphalt, concrete) slow wetting and drying 9
  10. 10. SOIL TEMPERATURE • Heat loading: incoming radiation absorbed and re-radiated by buildings and streets; low vegetative cover so most reaches soil •  heat • - day and night air temperature (0.5-1.5C) -10-20%  wind speed -2-10%  relative humidity -5-10%  clouds and total rainfall 10
  11. 11. ORGANIC MATTER • Low inputs (leaves and litter cleared away) • Low biological activity • Few or no earthworms • Results in  fertility 11
  12. 12. • Concentration of a substance in soil above background levels; may exceed toxicity threshold • Deliberate dumping or application, storage, wet or dry deposition, transport from overland flow, remnant materials 12
  13. 13. SOLIDS • Paper, glass, metals, plastic, masonry, brick, concrete, asphalt, processed wood • Potential sources of contaminants (e.g., Cu, Zn, B, Pb) • Plastics: decomposition can release toxic compounds or harmful gases • Iron & steel: release iron to form new compounds (e.g. insoluble iron phosphate) Liquids • Industrial wastes • Sewage effluents • Sludges • Industrial washwater • Runoff 13
  14. 14. GASES • Landfills: methane, CO2 (plus traces of CO, ethane, HS, NH3, ethylene, propylene, hydrogen cyanide) displace atmospheric gases (incl. O2) and alter redox status in the overlying soil • Gasoline leaks • Buried industrial wastes 14
  15. 15. HEAVY METALS • Atmospheric deposition of metallic aerosols from fossil fuel combustion, power plants, industrial processes. • Absorbed by plants and soil organisms • Persistent; slow leaching from the soil 15
  16. 16. WHY DO WE CARE? • Contaminants: contact with polluted soil through recreation (children especially vulnerable), urban gardening programs (food chain), volatilization • Street trees and green spaces: plant health may be severely restricted • Soil is largely a non-renewable resource; as larger and larger areas become urbanized we need to find ways to maintain good soil condition 16
  17. 17. HEALTH IMPLICATIONS • Exposure to industrial contaminants is linked to health effects such as asthma, stillbirths, miscarriages, neurological disease, and cancer • Effects on domestic animals, wildlife and fish 17
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Urban Soil By Saad Farooqi


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