ENVS10001 Lecture Notes - Lecture 5: Gully, Weathering, Surface Runoff
17 May 2018
School
Department
Course
Professor
SOILS + LANDSCAPES
Field Description of Soil Properties
• Reasons for differences in soil + why they have horizons
Parent Material
• Rock (or sediment), + combination of minerals within give rise to soil properties + secondary
minerals present in soil
Climate
• Temperature: affects rate of mineral weathering + synthesis of soil
o Affects rate of chemical weathering reactions
o Affects diffusion (water) of weathered products
o Biological growth + decomposition enhanced
" 3x increase in microbial activity for each 10° rise in temperature
• Moisture: under wet/humid conditions, moisture can accelerate mineral weathering + soil
formation
o Increases net downward movement of soil
o Increases leaching of soluble materials
o Increases translocation of clay particles
Relief
• Affects local climate, vegetation + drainage of landscape
• Angle of slope affects proportion of surface run-off to infiltration
o Well drained at top of slope, poorly drained toward
lowlands ! seen in colour gradient
Organisms
• Plant growth ! soil cover reduces erosion
• Soil invertebrates (ants, termites, earthworms) ! increase soil structure, + displace lower
horizons to surface (pedoturbation)
• Microorganisms breakdown organic matter
Time
• Less minerals + organic matter over time
• Depletion of CaCO over time ! change in pH
Dispersion
•Dispersion: is a process that occurs in soils that are particularly vulnerable to erosion by
water
•Rain causes soil to disperse which clogs up pores ! forming puddles
•Puddle evaporates + surface soil crusts
oBig agricultural implications: crust bad for plant growth (inhibits seed coming to
surface after germination) + water can’t permeate through crust
•Increase in salinity of water reduces dispersion + therefore turbidity of water
•Gully erosion often associated with dispersion
