Chapter 13. Erosion and Sedimentation. Soil Erosion. The biggest threat to agricultural and forestry production worldwide. Soil is the basis of much of the wealth on this planet;
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Erosion and Sedimentation
Each dot represents 250,000 tons. Total US soil loss in 1997 was 2 billion tons. The worst erosion occurs in the Mississippi Valley and the Midwestern corn belt. These areas have silty soils, rolling topography, and intensive farming.
“The soil which kept breaking away from the highlands keeps continually sliding away and disappearing into the sea. What now remains, compared with what existed earlier, is like the skeleton of a sick man, all the fat and soft earth having wasted away and only the base framework of the land being left.
“What are now mountains were lofty soil-clad hills; the stony plains of the present day were full of rich soil, the mountains were heavily wooded - a fact of which there are still visible traces. There are mountains in Attica which can support nothing but bees but which once were clothed, not so very long ago, with fine trees suitable for roofing the largest buildings - and roofs hewn from the timber are still in existence. The country produced boundless pastures for cattle.
“The annual supply of rainfall was not lost, as it is at present, through being allowed to flow over the denuded surface into the sea, but was received by the country, into her bosom, where she stored it in her impervious clay and so was able to discharge the drainage of the heights into the hollows in the form of springs and rivers with an abundant volume and a wide territorial distribution. The shrines that survive to the present day on the sites of extinct water supplies are evidence for the correctness of my present hypothesis.”
High < 25 mg/L
Moderate 25 - 80
Low 80 - 200
Very Low > 200
1. The streams most commonly degraded in Georgia by sediment today are: (choose one)
a. agriculture b. forestry c. urban d. mountain
2. Why does Georgia have such high erosion? (choose any/all/none)
a. steep slopes b. erodible soils c. intense rainfall d. land-disturbing activities
a. Suspended Solids _____ Clarity of lake water
b. Turbidity _____ Sands on streambed
c. Bedload _____ Filterable solids
d. Secchi Depth _____Clarity of river water
4. Give two reasons why we are concerned about erosion:
5. (True/False) Soil mulch and seeding is less effective than silt fences and hay bales for preventing erosion.