Soil erosion Essay

This essay has a total of 2239 words and 12 pages.

Soil erosion




SOIL EROSION

Soil erosion is a gradual process that occurs when the actions of water, wind, and other
factors eat away and wear down the land, causing the soil to deteriorate or disappear
completely. Soil deterioration and low quality of water due to erosion and run off has
often become a severe problem around the world. Many times the problems become so severe
that the land can no longer be cultivated and is abandoned. The key to minimizing soil
erosion and saving the farm lands is the farmer himself. Ultimately, he is the one who
must reduce the level at which erosion sediments are dislodged from his cropland. This
program will discuss the erosion process, its effects on crops and the environment, and
the Best Management Practices that can be implemented to limit or contain soil movement
from the land.


TYPES OF EROSION
Soil erosion can be divided into two very general categories:
Geological erosion: Geological erosion occurs where soil is in its natural environment
surrounded by its natural vegetation. This has been taking place naturally for millions of
years and has helped create balance in uncultivated soil that enables plant growth. A
classical example of the results of geological erosion is the Grand Canyon.


and Accelerated erosion: Accelerated erosion can be caused by man's activities, such as
agriculture and construction, which alter the natural state of the environment.

Accelerated erosion is the type that will be covered in most depth. It includes such problems as


wind erosion
The action of wind on exposed sediments and friable rock formations causes erosion
(abrasion) and entrainment of sediment and soil. Eolian action also forms and shapes sand
dunes, yardangs (streamlined bedrock hills) and other landforms. Subsurface deposits and
roots are commonly exposed by wind erosion. Wind can also reduce vegetation cover in wadis
and depressions, scattering the remains of vegetation in interfluves. Stone pavements may
result from the deflation (removal) of fine material from the surface leaving a residue of
coarse particles. Blowouts (erosional troughs and depressions) in coastal dune complexes
are important indicators of changes in wind erosion. The potential for deflation is
generally increased by shoreline erosion or washovers, vegetation die-back due to soil
nutrient deficiency or to animal activity, and by human actions such as recreation and
construction.

SIGNIFICANCE: Changes in wind-shaped surface morphology and vegetation cover that
accompany desertification, drought, and aridification are important gauges of
environmental change in arid lands. Wind erosion also affects large areas of croplands in
arid and semi-arid regions, removing topsoil, seeds and nutrients.

HUMAN OR NATURAL CAUSE: Eolian erosion is a natural phenomenon, but the surfaces it acts
upon may be made susceptible to active wind shaping and transport by human actions,
especially those, such as cultivation and over-grazing, that result in the reduction of
cover vegetation.

ENVIRONMENT WHERE APPLICABLE: arid and semi-arid lands
TYPES OF MONITORING SITES: Dune fields, coastlines, desert surfaces
SPATIAL SCALE: patch to landscape / mesoscale to regional

METHOD OF MEASUREMENT: Field observations, aided by airphotos and field surveys. Changes
in vegetation cover can be monitored using historical records, sequential maps, air
photos, satellite images, and by ground survey techniques.

FREQUENCY OF MEASUREMENT: Every 5-20 years
LIMITATIONS OF DATA AND MONITORING: The effect of wind erosion on different rock types and
landforms (with contrasted aerodynamic shapes) varies, so that it is not easy to assess
the degree of erosion of a complex landscape.

APPLICATIONS TO PAST AND FUTURE: Differential erosion by wind in the past may be detected
through study of buried soil horizons developed on ancient erosional surfaces, which
formed during dry (wind erosion) to wet (soil formation) climatic cycles.

POSSIBLE THRESHOLDS: Sediment erosion and transport takes place within a specific range of
wind speeds, depending on grain size, degree of cementation and compaction, moisture
content, and vegetation cover.

Differential erosion by wind in the past may be detected through study of buried soil
horizons developed on ancient erosional surfaces, which formed during dry (wind erosion)
to wet (soil formation) climatic cycles.


Water erosion:
Raindrops can be a major problem for farmers when they strike bare soil. With an impact of
up to 30 mph, rain washes out seed and splashes soil into the air. If the fields are on a
slope the soil is splashed downhill which causes deterioration of soil structure. Soil
that has been detached by raindrops is more easily moved than soil that has not been

detached. Sheet erosion is caused by raindrops. Other types of erosion caused by rainfall
include rill erosion and gullies.

caused by rain and poor drainage. Three types of erosion are:
o Sheet erosion: Sheet erosion is defined as the uniform removal of soil in thin layers
from sloping land. This, of course, is nearly impossible; in reality the loose soil merely
runs off with the rain.

o Rill erosion: Rill erosion is the most common form of erosion. Although its effects can
be easily removed by tillage, it is the most often overlooked. It occurs when soil is
removed by water from little streamlets that run through land with poor surface draining.
Rills can often be found in between crop rows.

o Gully erosion: Gullies are larger than rills and cannot be fixed by tillage. Gully
erosion is an advanced stage of rill erosion, just as rills are often the result of sheet
erosion.


BRIEF DESCRIPTION: Erosion, the detachment of particles of soil and surficial sediments
and rocks, occurs by hydrological (fluvial) processes of sheet erosion, rilling and gully
erosion, and through mass wasting and the action of wind. Erosion, both fluvial and eolian
(wind) is generally greatest in arid and semi-arid regions, where soil is poorly developed
and vegetation provides relatively little protection. Where land use causes soil
disturbance, erosion may increase greatly above natural rates. In uplands, the rate of
soil and sediment erosion approaches that of denudation (the lowering of the Earth's
surface by erosional processes). In many areas, however, the storage of eroded sediment on
hillslopes of lower inclination, in bottomlands, and in lakes and reservoirs, leads to
rates of stream sediment transport much lower than the rate of denudation.

When runoff occurs, less water enters the ground, thus reducing crop productivity. Soil
erosion also reduces the levels of the basic plant nutrients needed for crops, trees and
other plants, and decreases the diversity and abundance of soil organisms. Stream sediment
degrades water supplies for municipal and industrial use, and provides an important
transporting medium for a wide range of chemical pollutants that are readily sorbed on
sediment surfaces. Increased turbidity of coastal waters due to sediment load may
adversely affect organisms such as benthic algae, corals and fish.

SIGNIFICANCE: Soil erosion is an important social and economic problem and an essential
factor in assessing ecosystem health and function. Estimates of erosion are essential to
issues of land and water management, including sediment transport and storage in lowlands,
reservoirs, estuaries, and irrigation and hydropower systems. In the USA, soil has
recently been eroded at about 17 times the rate at which it forms: about 90% of US
cropland is currently losing soil above the sustainable rate. Soil erosion rates in Asia,
Africa and South America are estimated to be about twice as high as in the USA. FAO
estimates that 140 million ha of high quality soil, mostly in Africa and Asia, will be
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