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Land degradation

Types of Land Degradation

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Land degradation

  2. 2. Land Degradation • Definition: • Causes: Any change that decreases productivity of the land -Land clearing -Poor land management practices 2
  3. 3. • Poor land management practices include grazing of stock that has hard hooves, growing of crops that require large amounts of fertilisers and pesticides especially superphosphate and nitrogen, and irrigation for crops on sandy soils. 3
  4. 4. Water Erosion • Definition: removal of soil particles by heavy rainfall or running water 4
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  6. 6. • Soil is washed downhill beneath the surface with a resultant collapse of the unsupported surface soil which results in an undermining and subsidence of the banks of flooding rivers and creeks. • Under normal conditions, where slopes have vegetation cover; there is less surface runoff and more water is infiltrated into the soil. The vegetation forms a layer of humus (leaf litter) on top of the top soil layer and this helps to stabilise soil movement. • Under conditions where there is no vegetation cover, there is major surface runoff, and this carries loose soil with it, as there is no humus layer to stabilise the soil. Also making rills and channels. The soil particles can be washed into waterways and deposited at the base of slopes. 6
  7. 7. Sheet Erosion • Caused by soil particles being transported with runoff on a downhill slope causing other layers of soil and rock to be exposed. 7
  8. 8. Rill Erosion • Caused by no vegetation cover and increased water movement downslope. The movement carries loose soil and also makes rills into the side of the slope. 8
  9. 9. Gully Erosion • As major volumes of water moves downslope, channels form and the soil is deposited at the base of the slope. This is caused by no vegetation cover. 9
  10. 10. • If soil is washed into waterways it increases the turbidity (muddiness) of the water. This is because the sediments are suspended in the water. 10
  11. 11. Wind Erosion • Definition: This is when loose soil particles are collected by the wind and transported to another location. • It happens in areas which have sandy soils and low rainfall 11
  12. 12. Strategies for reducing wind erosion • minimising the amount of time that the soil has no vegetation cover • increasing vegetation cover and decreasing stock rates 12
  13. 13. • Eliminating introduced animals which strip vegetation eg. rabbits 13
  14. 14. • Building contour banks (raised areas of soil along slopes to reduce water downslope) • Ploughing across slopes not down the slope • Planting trees to form windbreaks 14
  15. 15. Salinity • Primary Salinity CAUSE: low, erratic rainfall high evaporation rates When there is not enough water to leech out salts from soil, (which occur naturally), the salt forms a crust and rises to the surface as the moisture in the soil is evaporated. Usually in this situation there is no waterways to help flush the salty areas. 15
  16. 16. • Secondary Salinity CAUSES: -Man made activities that alter the natural balance of the catchment area. -There is movement of the soil profile (the layers of different types of soil and minerals) and groundwater. -There is extra water added to the groundwater by irrigation or vegetation is cleared. 16
  17. 17. Dryland Salinity 17
  18. 18. Indicators: Seeps (seepage areas) 18
  19. 19. • Scalds Occur when water or wind erosion removes the topsoil exposing the salty subsoil 19
  20. 20. When the native vegetation has been removed, and crops and pastures that have shallow root systems, the subsoils have been destabilised. Watertables have risen bringing dissolved salts to the surface. Rivers are experiencing salinisation by the dissolved salts being collected in surface runoff and washed into the waterways and therefore polluting them. Major filtration has to occur to make it palatable (able to be used for drinking water). 20
  21. 21. • Irrigation Salinity The water seeps through the soil causing the water table to rise. The dissolved salt in the soil makes it’s way into the vegetation root system, and therefore causing it to die. Salination can also occur through salty surface runoff, caused by too much irrigation. 21
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  23. 23. How can salinity be managed? • Plant deep rooted vegetation to reduce groundwater recharge and increases evaporation through plants (evapotranspiration). • Proper drainage and pumping of irrigation • The problem can not be looked at in isolation from other land management problems. Total Catchment Management needs to be employed. 23
  24. 24. Total Catchment Management AIM: To reduce degradation of soils and water in a catchment area. This takes into account all available resources and uses in the area. The decisions are made by government agencies, services, farmers, industries, communities and recreational users. Each group must work to achieve the best decision. 24