Discuss the causes and effects of soil erosion in East Africa

Candidates are expected to define soil erosion as the removal/washing away of the top thin layer of soil by agents like wind, running water, glaciers etc. transported and deposited in  some other place.

Candidates should identify areas in East Africa where soil erosion occurs e.g. highland areas like Kabale, Elgon, Kenya highlands. Other areas like Kondoa region in Tanzania, dry areas like Ankole – Masaka corridor, Kotido, Machakos in Kenya etc.

Candidates are expected to bring 0ut types/processes of soil erosion which include:

• Splash erosion caused by the impact of rain drops which dislodge rock partic1es and scatter them in several directions.
• Sheet erosion which involves uniform removal of a thin layer of soil mainly on gentle slopes.
• Rill erosion which is the uneven removal of surface soil by running water in small channels/furrows as rills.
• Gulley erosion is where wide channels/grooves are created by running water. Common in areas with steep slopes and areas which receive heavy rainfall.
• Deflation by wind which removes soil material from one part of the earth’s surface to another. Common in arid areas.

Candidates are expected to bring out the causes of soil erosion in which are both physical and human factors.

Physical factors include the following;

• Climate through heavy short torrential rainfall results into run off and loss of soil through surface flow.
• Prolonged but gentle rainfall leads to minimal erosion.
• Presence of strong winds especially in areas of very-low rainfall lead to wind erosion.
• Relief/topography: Steep gradients especially in highland areas accelerate the rate of soil erosion causing massive gullies.
• Gentle slopes encourage sheet erosion.
• Scanty or limited vegetation cover may also lead to soil erosion e.g. areas of limited vegetation cover experience high rates of erosion like wind erosion yet areas of thick vegetation cover, the rate of soil erosion is reduced e.g. areas of Mabira forest.
• Nature of soils also influences soil erosion. The poor porous and unconsolidated soils offer less resistance to forces of wind and running water e.g. volcanic soils, sandy soils leading to soil erosion.
• Biotic factors like harvester ants common in pastoral and semi-arid areas eat all the grasses leaving the land bare such that wind or runoff water easily carry away the soils leading to soil erosion.

The human factors include the following;

• Deforestation which is the clearing of forests by man reduces the protective cover of soil and encourages run off which leads to soil erosion in form of sheet, gulley etc.
• Overgrazing/overstocking: The large herds of animals lead to emergence of bare patches of land. Such land is easily eroded by agents of erosion especially in areas of nomadic pastoralism.
• Bush burning by pastoralists e.g. Bahima, Masai in Kenya, Tanzania and cultivators distort the soil binding factors. It exposes soil to agents of erosion like wind and running water thus sheet, rill and wind erosion.
• Monoculture which is the persistent growing of a single crop on a particular piece of land which leads to soil exhaustion. The soils are left loose and can easily be carried away by agents of erosion.
• Up and-down slope cultivation without using proper methods of cultivation along the slope encourages run off leading to gulley erosion on steep slopes.
• Over cropping which involves continuous cultivation and growing of crops on the same piece of land for a long time without putting it to rest, leads to soil exhaustion. The soils become loose and are easily washed away by agents of erosion.
• Mining/quarrying accelerates the rate of soil erosion because the vegetation cover is removed and land is left bare prone to soil erosion.
• Construction works e.g. roads and railway construction lead to exposure of soil leaving it unprotected and exposed to harmful effects of rain drops and running water. In addition running water easily takes advantage of transport routes to create gullies paving way to soil loss.
• Growing of poor cover cropsg. cotton, tobacco, leaves bare land in between the rows that easily encourage soil removal by running water.

Candidates are expected to bring out effects of soil erosion which are both positive and negative

The negative effects of soil erosion include

• Loss of soil fertility leading to unproductive soils which lead to low crop yields thus famine/hunger.
• Creates waste land/ Bad Lands with gullies that hinder transport and communication as well as mechanization.
• Wind erosion leads to water and air pollution due to sand dust.
• Flooding in broad river valleys due to siltation leading to destruction of property and lives.
• Results into limited vegetation cover because badly eroded soils are unable to support plant growth. This results into problems e.g. reduced transpiration, scarcity of pastures for animals.
• Dust, particles earned by wind are deposited on social infrastructure like roads, buildings etc. leading to increased costs of maintenance.
• The positive effects of soil erosion include:
• Alluvial soils are transported and deposited in low lands which soils are fertile and can be used for farming/ growing of crops.
• Soil erosion exposes Isenberg which attract tourists thus promote tourism industry.
• Soil erosion exposes minerals that can be mined like granites and limestone and when exported, revenue is earned.
• Removal of top soil exposes the parent rock to agents of weathering leading to formation of fresh/new soils.

NB: candidates should put a lot of emphasis on causes of soil erosion.