CEPSCI Soil Science and Erosion Fundamentals 2 — Questions and Answers
Question 1: What role does organic matter play in soil erodibility?
- Organic matter increases soil erodibility by making it lighter
- Organic matter decreases erodibility by improving soil aggregate stability, water-holding capacity, and infiltration (Correct answer)
- Organic matter has no effect on erosion
- Organic matter increases runoff by repelling water
Correct answer: Organic matter decreases erodibility by improving soil aggregate stability, water-holding capacity, and infiltration
Organic matter binds soil particles into stable aggregates that resist raindrop impact and runoff, and it improves infiltration, both of which reduce erosion.
Question 2: Which soil horizon is typically most vulnerable to erosion when exposed by construction grading?
- The A horizon (topsoil) before it is removed
- The B or C horizon subsoils exposed after topsoil stripping (Correct answer)
- The bedrock layer
- The O horizon of organic matter
Correct answer: The B or C horizon subsoils exposed after topsoil stripping
Subsoil horizons (B and C) typically have poor structure, low organic matter, and high clay content, making them more erodible and difficult to revegetate than topsoil.
Question 3: What is 'soil erodibility' as measured by the K factor in the USLE?
- The ability of soil to resist compaction by heavy equipment
- The susceptibility of soil to detachment and transport by rainfall and runoff (Correct answer)
- The ability of soil to support plant growth
- The drainage rate of soil under saturated conditions
Correct answer: The susceptibility of soil to detachment and transport by rainfall and runoff
The K factor quantifies how easily a specific soil type is detached by rainfall and transported by runoff, integrating texture, structure, organic matter, and permeability.
Question 4: What is the effect of vegetative cover on soil erosion rates?
- Vegetation increases erosion by loosening soil with roots
- Vegetation dramatically reduces erosion by intercepting rainfall, binding soil with roots, and slowing runoff (Correct answer)
- Vegetation has no significant effect on erosion
- Vegetation only reduces erosion in dry climates
Correct answer: Vegetation dramatically reduces erosion by intercepting rainfall, binding soil with roots, and slowing runoff
A well-established vegetative cover can reduce erosion by more than 99% compared to bare soil by intercepting raindrop energy, increasing infiltration, and binding soil particles with roots.
Question 5: What is 'gully erosion' and why is it significant on construction sites?
- Erosion that occurs only in sandy coastal areas
- Advanced-stage erosion where rills merge into large, deep channels that cannot be crossed by equipment, indicating severe loss of soil (Correct answer)
- Erosion that occurs only below the water table
- Minor surface staining that does not involve soil loss
Correct answer: Advanced-stage erosion where rills merge into large, deep channels that cannot be crossed by equipment, indicating severe loss of soil
Gully erosion represents extreme concentration of runoff that has cut deeply into the soil, removing large volumes of material and potentially destabilizing adjacent areas.
Question 6: How does the slope length factor (L) in the USLE affect predicted soil loss?
- Longer slopes always have less erosion than shorter slopes
- Longer slopes allow more runoff to accumulate and accelerate, increasing erosive power and predicted soil loss (Correct answer)
- Slope length has no effect on erosion calculations
- Shorter slopes have higher erosion rates because water moves faster on them
Correct answer: Longer slopes allow more runoff to accumulate and accelerate, increasing erosive power and predicted soil loss
As runoff travels down a longer slope, it accumulates more volume and velocity, increasing its erosive energy and the quantity of sediment it can transport.
CEPSCI Soil Science and Erosion Fundamentals 2
What role does organic matter play in soil erodibility?