Processes and Causes of Degradation

Higher Geography: Rural Land Degradation

Introduction (1)

RLD is usually the result of unreliable climate (eg : periods of drought with occasional heavy rain), combined with poor agricultural practice.

There are three kinds of action that commonly lead to land degradation :PhysicalBiologicalChemical

Introduction (2)

The impact of human activity on the land intensifies these actions, contributing to accelerated land degradation.

These human activities include deforestation, overgrazing (both linked to population pressure) and poor agricultural practice.

Physical Action (1)

Physical action can cause the soil to become more compact - where land is frequently used by humans (walking, animal hooves, heavy machinery etc.)

This wear and tear destroys plants and leaves bare earth open to the weather and erosion.

Physical Action (2)

Compact soil without vegetation cover often prevents water from penetrating the soil, causing run-off at the surface which in turn accelerates soil erosion.

Extreme physical damage where quarrying and open-cast mining our found.

Biological Action (1)

Biological action usually takes the form of removing the living cover of vegetation (trees, grass etc.)

The removal of vegetation means that less rainfall can be intercepted. More rain falls directly on to the soil and it can be washed away much more rapidly, increasing soil erosion.

Biological Action (2)

In dry areas of the world, any removal of vegetation will increase the power of the wind to cause soil erosion.

Other biological action can result from plant diseases or locust attacks.

Chemical Action (1)

Chemical action occurs where farmers overuse soil, this means that :

minerals are often not replacedthe soil become less able to support plantsthe organic content of the soil is reducedits structure is loosened and more easily removed by rain and wind

Chemical Action (2)

Soil contamination can also occur through :

acid rainfallthe dumping of hazardous industrial wasteoveruse of fertilisers and pesticides

Soil Erosion by Water

There are 4 types:

Rainsplash is concerned with the impact of raindrops on the surface of a soil.

Sheet wash is the removal of a thin, almost unseen, layer of surface soil.

Rill erosion is the creation of a very small eroded channels across a soil surface.

Gully erosion is the creation of large gullies by large quantities of water flowing over the soil surface.

Rain Splash

The bigger the raindrop, the faster it hits the soil.

A drop of rain causes soil to splash. Gravity causes more particles to move down than up slope.

Sheetwash

The rainsplash effect can also clog up the soil, leading to a form of soil erosion called sheet wash.

The tiny soil particles which are displaced during rainsplash find their way into soil pore spaces located between soil crumbs and clog them up.

The result is the formation of a surface crust (1mm think), but the rate at which rainwater can now infiltrate the soil is now reduced.

Rill and gully erosion

These are the most serious form of soil erosion by running water.

Most land surfaces are irregular, with natural depressions, slopes and channels. A sudden burst of rainwater, which is unable to soak into the soil will flow over the surface, finding its way into natural channels.

Here it will gather in volume, power and speed as it makes its way down slope. Dislodging and moving soil particles down slope as it goes.

The difference between Rill and Gullies

Gullies are steep sided water channels which carry water only during rainstorms and , unlike rills, are a permanent feature on the landscape.

Soil Erosion by Wind

• Loss of topsoil in one area

• deposition of material in another area where it can:

• form topsoil

• clog waterways

• cause air quality problems

Wind erosion has two types of impacts:

Suspension

SaltationCreep

Wind

Mechanisms of wind erosion

Light areas show where topsoil has been eroded.

Deposition of topsoil along fence lines.

Dust Bowl - US 1920’s-30’s

Includes: •Stunted growth -wind “pruning”

•Physical damage - especially if carrying sand particles (tall plants may be flattened)

•Transporting pests

Effects of wind on plants

Reduce crop yields and/or quality

Prevailing wind

Wind pruning

Positive wind effects

Pollination

Reduce humidity in canopy - reduce disease potential