land degradation Flashcards
Land degradation
defined as the long-term loss of ecosystem function and productivity caused by disturbances from which the land cannot recover unaided
Land degradation processes
Erosional processes -where erosional agents such as wind, water and ice are responsible for detachment, transport and deposition of materials.
mainly acting upon the slope surface or a limited column of soil or unconsolidated material. E.g.rill erosion
Denudational processes -where gravitation is the main driver for the down slope movement of soil and rock. Mass wasting is often used as a synonym, just as the general term mass movement.
are not restricted to the slope surface but can be deep-seated and affect the slope profile to a considerable depth.E.g.landslideLAND DEGRADATION PROCESSES
Causes of land degradation
1.Anthropogenic –human induce
✓Change of land use, e.g.deforestation
✓Housing development, road construction
✓Agriculture
✓Livestock: grazing and soil compaction
✓Forest fire
2.Natural –natural event
✓Strength of eroding agent (velocity, mass)
✓Soil properties (texture, structure, cohesion)
✓Soil surface coverage
✓Soil moisture level
✓Plant root systems in the soil
✓Slope of the land
✓Average soil grain size
Soil erosion: the cause of Land Degradation
Soil Erosion -is the process of detaching the soil particles by erosive agents such as water, wind and ice from the land’s surface of one place and its transportationto another place for deposition.
*Soil erosion is a naturally occurring process of wearing down landforms by the combined actions of gravity, water, wind and other forces.
SOIL EROSION TYPES
Water -Water erosion
▪Raindrop / Splash erosion
▪Sheet / Rill erosion
▪Gully erosion
▪Stream bank erosion
Wind-Wind erosion
ice- glaciers: plucking, abrasion, freeze thaw
a. USA is losing soil ………….. faster-and China and India……………… faster-than the natural soil replenishment rate.
b. damage from soil erosion worldwide is estimated at US…………..per year
c. over the past 40 years, …………..of the worlds arable land has become unproductive due to soil erosion
d. about ………. of soil that is washed away ends up in river streams and lakes, making waterways more prone to flooding and to contimation from soils fertilizers and pesticides.
e. Together, wind and water erosion account for of all …………………land degradation
a. 10times,30 to 40 times
b.$ 400 billion
c. 30 %
d.60 %
e.84%
main erosive agents,wind and water erosion, water erosion is the largest contributor to global land degradation at …….., while wind erosion accounts for half of this at …….
56%, 28%
soil erosion types- water erosion
rain storm and rain drop splash
Overland flows or surface run-off-
There are 2 types of overland flow:
*infiltration excess overland flow *saturation excess overland flow
water erosion process
. detachment- causes of detachment
b . tillage practises
c. trampling by people or livestock
d. rainsplash
e. flowing water
transport-
Sediment
transport by
water is a complex process driven largely by gravitational forces moving sediment down slope by over land or river flows from a source area to a
sink area where sediment is eventually deposited.▪Where,how much and how far sediment is transported ,is a very tricky thing to determine.▪Sediment transport occurs in shallow overland flow and in stream or river channels.
deposition-Deposition can be triggered by changes in the speed or velocity of over-land flow through reductions in surface slopes.This reduction in slope, reduces the speed of overland flow and also the ability of the flow to continue to transport its sediment load.Thus resulting in deposition.
Forms of Water Erosion
❖Sheet or interill erosion-Uniform removal of thin layer of soil either by runoff or wind
*discoloration at the soil surface is a clue that sheet erosion has removed the more productive near surface layers
❖Rill erosion-shallow overland flow, begins to concentrate water as it flows downslope. small channels drainage lines, < 30 cmdeepRills develop when surface water concentrates into depressions or low points in field causing it to erode
❖Gully erosion-
Advanced forms of rill erosion, depth > 50 cmOccurs when runoff concentrates and flows strongly enough to detach and move soil particlesThey are activated during high intensity but short duration rainfall events*more evident on hillsides when cleared of vegetations and where overgrazing occurs
❖Stream or river bank erosion-river under-cutting the banks by concentrating water along the channel margins*Presence of tree roots can help to minimize the rate and amount of bank erosion
❖Mass movement
causes of water erosion
a. fire
b. land management
c. Agricultural management
d. climate change
CAUSES OF EROSIONS
*Steep slope
*Poor ground cover
*High intensity rainfall
*Overgrazing
*Deforestation
*Forest fire
*Unsustainable land management
*Poor water management
*Erosive soils
reducing the effects of water erosion
3 principles:
1.Land capability : appropriate use of land
2.Surface cover: maintaining soil cover
Importance of surface coversurface cover is really a vital issue.It can be living plants,it can be residues of crops,but they protect the soil against the impact of the rainfall.*they provide more time for water to infiltrate into the soil.
3.Runoff control : minimising overland flow
MITIGATING MEASURES
Hedgerows
*Stone bunds
*Terracing
*Orchard basin
*Grass slip planting
*Cover & multiple cropping
*Control overgrazing, deforestation & forest fire
*Improve soil structure (organic fertilizers)
*Conservation tillage
*Mulching
WIND EROSION
where does it occurs
Wind erosion is the loss of soil due to the movement of wind
Wind erosion occurs: *On dry lands
*On newly-ploughed fields
*On land where vegetation has been destroyed
*When there is high-velocity winds and dry soil
Wind erosion causes air pollution, produces highway safety hazards, and fills drainage ditches.
