On-site and off-site consequences of soil

erosion

Prepared by: Santosh Pathak ( IAAS, Lamjung)

Soil erosion• Erosion refers to detachment and

transport of soil and soil materials by water, wind, ice or gravity.

• No soil phenomenon is more destructive worldwide than the erosion caused by wind and water.

• Erosion damages the site on which it occurs and also has undesirable effects off-site in the larger environment.

On-site Consequences:• The loss of soil itself.

• The damage done to the soil is greater than the amount of soil lost as the soil material eroded away is almost always more valuable than that left behind.

• In Nepal, the annual loss of soil from agricultural plots ranges from 0.1 t/ha to 105 t/ha (Chalise and Khanal)

• Erosion removes organic matters and fine minerals particles while leaving behind mainly relatively less active, coarser fraction.

• O.M and N2 in the eroded materials to be five times as high as in original top soils.

Fig: decline in soil productivity

On site consequences…• 1.8 tons of plant nutrients are removed from the soil

by crop harvest and soil erosion and only 0.3 million mt. (16%) are replenished by organic and inorganic fertilizers (MOEP, 2001)

• Eroded zone has lower water holding capacity and cation exchange capacity, less biological activity, less access to nutrients for plant.

• Erosion spread plant disease organisms.

• Deterioration of soil structure

• Dense crust formation

• Reduce water infiltration

• Increases water runoff

• Seed and seedlings may be washed downhills.

• Uprooting of trees.

• Small plants buried in sediments

Fig: Tree being uprooted

Fig: Small plants buried in sediments

• In the case of wind erosion : Fruits and foliage damaged

by the sand blasting. leaf incrustation causes

stomatal closening.

• Relatively large gullies make the use of tractors impossible.

• Under cut pavements and building foundation : unsafe conditions and expensive repairs.

Fig: Gully erosion

Fig: Difficulty in transportation due to gullies

Off site damages

• Movements of sediments and nutrients off the land, creates two most widespread water pollution.• eutrophication caused by

excessive nitrogen and phosphorus.

• Carry toxic metals and organic compounds such as pesticides, leads to bio magnification.

Damages from sediments Smother crop and low growing

vegetation. Roadside drainage and ditches

filled creating hazardous driving conditions.

Turbidity of streams increased preventing sunlight penetration and reduced photosynthesis and survival of submerged aquatic vegetation(SAV).

Fig: Water turbidity increased due to soil erosion

Contd……

The demise of SAV, in turn, degrades the fish habitat and upsets the aquatic food chain.

Spawning sites of the freshwater fishes buried. According to the WWF, a group of Brazilian Indians

reported significant decreases in fish numbers. Bottom sediments buildup raise the level of river

causing frequent and severe flooding. Koshi river of Nepal is a popularly noted for its

sediment transportation, it occurs in 6th position with 172 million tons/annum sediment transportation.

The life span of kulekhani reservoir in the central Nepal has been reduced to half of the targeted design and one quarter of the expected life due to soil erosion.

Reservoir capacity is decreased. Very high cost of remedy operations like excavation,

filtering, and construction activities. Fig: Reservoir exceeds its capacity

Contd…..

• In case of wind erosion, blowing sand may bury roads and fill drainage ditches, necessitating expensive maintainance.

• Sand blasting effect damage the fruits and foliage of the field as well as paint on vehicle and building.

• Dust storms and air pollution cause discomforts, disease infections, automobile accidents etc.

• Change in landforms and topography.

Fig: Adverse effects on humanhealth caused by pollution

Fig: Formation of canyon due to erosion

• Combating soil erosion is everybody's business.

attention must be paid to control on site consequences which finally reduce off site consequenses.