Topic 3.8.3 Describe three stages of soil formation

1. Topic 3.8.3 Describe three stages of soil formation Environmental Systems Roland Schmidt-Bellach Changes made by Darlene Oehlke

2. Soils • Soils are an important natural resource. They represent the interface between the atmosphere, hydrosphere, lithosphere and the biosphere! Soils provide nutrients for plants.

3. Weathering • Mechanical weathering: a physical change: Rocks are broken into smaller pieces • Chemical weathering: Chemical reactions change the soil composition over time • Biological weathering: Plants and animals change the soil, adding organic matter and nutrients through decomposition

4. Stage 1 - Mechanical weathering The rock is physically broken into smaller pieces largely from: • Temperature changes, breaking rocks • Ice creating cracks in rocks

5. Mechanical Weathering • Temperature changes from sunlight • Rapid heating and cooling causes rocks to expand and contract resulting in them breaking down • Typical weathering in arid regions

6. Mechanical Weathering – Ice or frost shattering

7. Ice

8. More Mechanical Weathering • Sand and other hard objects are blown against the parent rock, physically breaking away materials into smaller pieces.

9. Mechanical Weathering – Ocean surf • Ocean surf near Tamarindo beach in eastern El Salvador pound the coast breaking down coastal rock formations

10. Mechanical Weathering – Glaciers break stones • Glaciers grind rocks into powder (rock flour or fine clay).

11. Mechanical Weathering - Glaciers • Moraines or sand & gravel deposits (hills) are left behind.

12. Chemical weathering • Chemical reactions change the composition of the rock. • Plant acids react with rock • Acidic rain reacts with the rock • Oxidation of rocks and particles (reaction of oxygen in the air)

13. Chemical weathering - oxidation • The stones react with oxygen in the air.

14. Plant acids react with rock

15. Acid in rain reacts with stone

16. Stage 2 - Chemical Weathering • Temperature (chemical): For every 10°C rise in mean soil temperature, the rate of biochemical reactions doubles. • Tropical soils will also weather faster because the chemical reactions will be taking place faster and the reactions will occur throughout the year.

17. Leaching • Water moves minerals out of upper soil layers to lower layers and/or to streams and rivers • Leaching is when heavy rainfall moves nutrients from the soil.

19. Chemical Weathering – Oxidation & Leaching • Oxidation: the ‘rusting’ or breakdown of minerals (metals) exposed to oxygen and water. • Leaching: water dissolves substances and carries them deeper in the soil profile.

20. Chemical weathering – acid conditions • More leaching occurs if the rain is acidic. • Acidic rain also reacts with the rocks and weathers them • Areas that are cool and wet will have more leaching compared to areas that are hot and dry • More of the rainfall in a hot climates evaporate back into the atmosphere before leaching can occur.

21. Stage 3 – Biological Weathering • Decomposition of organic material by bacteria breakdown living matter and waste into re-usable minerals for plants. • Soil fertility, porosity, and its ability hold water are increased.

22. Stage 3 – Biological Weathering • Soil is mixed by organisms including worms, insects, snails and molluscs.

23. Soil composition depends on: • Parent material (type of rock the soil is made of) • Climate of the region: precipitation, temperature, solar radiation • Plants and animals living on the soil (add organic matter and nutrients • Age of the soil

25. Soil formation takes a long time • The time required for soil formation is much slower than erosion (hence, soil is a non-renewable resource). • A one-meter thick soil developed in southern Wisconsin, USA in 8000 years • A one-meter thick soil in tropical arid Africa took 75,000 years to form. • Average global soil formation rate has been calculated to be 178 years per cm.

26. Topic 3.8.4 Human impact on soil formation Environmental Systems Roland Schmidt-Bellach

27. Desertification and Soil degradation • Overgrazing, poor farming practices, deforestation, improper irrigation methods, and careless land use cause soil to erode, to become degraded and to turn into desert.

28. Shoreline Erosion • Stable shoreline • Plants trap nutrients & water supporting more plants & biomass

29. Shoreline breakdown • Human recreation has removed the smaller vines and sand grasses. • Now storms (wind & water) have cut into the shoreline and removed sand.

30. Shoreline breakdown • This island in Fiji was nearly cut in half by a cyclone/hurricane as a result of deforestation.

31. Overgrazing • Palni Hills, southern India • All the top soil has been eroded due to livestock over grazing. • Over 30 cm of soil has been lost and mounds of the more resistant weathered bedrock remain.

32. Stream erosion • Kodaikanal, southern India • Over grazing, a steep slope and human/animal traffic cause the ground to slump into the steam and get washed away in the rainy season.

33. Salinization

34. Salinization • An aerial view over northern Australia shows how poor the soil is. • White ground patches indicate salinization. • Pale coloured soil show very low organic content, compaction, and high erosion potential.

35. Salinization • A severe case of salinization. • This field may never recover for planting.

36. Topic 3.8.5 Solutions to Human impact Environmental Systems Roland Schmidt-Bellach

37. Solutions to Erosion – contour farming

38. Erosion Prevention – slow the movement of water • Off contour swale used to collect runoff.

39. Off contour swales slow the movement of water

40. Erosion Prevention • Once constructed, swale systems can be planted to reduce erosion. • Deep rooted crops and trees can be planted to hold soil and generate $$.

41. Wind breaks – plant rows of trees • Wind breaks provide shade and slow the wind to reduce evaporation

42. Terracing on steeper slopes • Terracing is a technique that can be used to limit erosion. • Terraces should be planted so not to wash away.

43. Terrace Agriculture • Well established terraces. • Trees and bushes planted on terrace end can help hold it.

44. Agriculture Solutions • Contour or terrace farming limits erosion

45. Desperate Agriculture • Locals farm on steep slopes. • There is a lot of erosion.

46. Desperate Agriculture • What problems are presented here? • What are the solutions?