Light pollution, also known as photopollution or luminous pollution, is excess or obtrusive light created mainly by humans. Among other effects, and like any other form of pollution, it disrupts ecosystems, can cause adverse health effects, obscures the stars for city dwellers, and interferes with astronomical observatories. Light pollution can be construed to fall into two main branches: annoying light that intrudes on an otherwise natural or low light setting and excessive light, generally indoors, that leads to worker discomfort and adverse health effects. Since the early 1980s, a global dark-sky movement has emerged, with concerned people campaigning to reduce the amount of light pollution.
Light pollution is a side effect of industrial civilization. Its sources include building exterior and interior lighting, advertising, commercial properties, offices, factories, streetlights, and illuminated sporting venues. It is most severe in highly industrialized, densely populated areas of North America, Europe, and Japan and in major cities in the Middle East and North Africa like Cairo, but even relatively small amounts of light can be noticed and create problems. Like other forms of pollution, such as air, water and noise pollution, light pollution causes damage to the environment.
With recent advances in private spaceflight, the prospect of space-based orbiting billboards appearing in the near future has provoked concern that such objects may become another form of light pollution. With this in mind, the United States Federal Aviation Administration sought permission, in May 2005, to enforce a law prohibiting "obtrusive" advertising in earth orbit. Similar intentions are yet to be expressed by authorities in most other countries.
Impact on energy usage
Energy conservation advocates contend that light pollution must be addressed by changing the habits of society, so that lighting is used more efficiently, with less waste and less creation of unwanted or unneeded illumination. The case against light pollution is strengthened by a range of studies on health effects, suggesting that excess light may induce loss in visual acuity, hypertension, headaches and increased incidence of carcinoma[citation needed]. Several industry groups also recognize light pollution as an important issue. For example, the Institution of Lighting Engineers in the United Kingdom provides its members information about light pollution, the problems it causes, and how to reduce its impact.
Since not everyone is irritated by the same lighting sources, it is common for one person's light "pollution" to be light that is desirable for another. One example of this is found in advertising, when an advertiser wishes for particular lights to be bright and visible, even though others find them annoying. Other types of light pollution are more certain. For instance, light that accidentally crosses a property boundary and annoys a neighbor is generally wasted and pollutive light.
Disputes are still common when deciding appropriate action, and differences in opinion over what light is considered reasonable, and who should be responsible, mean that negotiation must sometimes take place between parties. Where objective measurement is desired, light levels can be quantified by field measurement or mathematical modeling, with results typically displayed as an isophote map or light contour map. Authorities have also taken a variety of measures for dealing with light pollution, depending on the interests, beliefs and understandings of the society involved. Measures range from doing nothing at all, to implementing strict laws and regulations about how lights may be installed and used.
Types
Light pollution is a broad term that refers to multiple problems, all of which are caused by inefficient, unappealing, or (arguably) unnecessary use of artificial light. Specific categories of light pollution include light trespass, over-illumination, glare, clutter, and sky glow. A single offending light source often falls into more than one of these categories.
Light trespass
Light trespass occurs when unwanted light enters one's property, for instance, by shining over a neighbor's fence. A common light trespass problem occurs when a strong light enters the window of one's home from outside, causing problems such as sleep deprivation or the blocking of an evening view.
A number of cities in the U.S. have developed standards for outdoor lighting to protect the rights of their citizens against light trespass. To assist them, the International Dark-Sky Association has developed a set of model lighting ordinances. The Dark-Sky Association was started to reduce the light going up into the sky which reduces visibility of stars, see sky glow below. This is any light which is emitted more than 90 degrees above nadir. By limiting light at this 90 degree mark they have also reduced the light output in the 80-90 degree range which creates most of the light trespass issues. U.S. federal agencies may also enforce standards and process complaints within their areas of jursidiction. For instance, in the case of light trespass by white strobe lighting from communication towers in excess of FAA minimum lighting requirements the FCC maintains a database of Antenna Structure Registration information which citizens may use to identify offending structures and provides a mechanism for processing consumer inquiries and complaints. The US Green Building Council (USGBC) has also incorporated into their environmentally friendly building standard known as LEED, a credit for reducing the amount of light trespass and sky glow.
Light trespass can be reduced by selecting light fixtures which limit the amount of light emitted more than 80 degrees above the nadir. The IESNA definitions include full cutoff (10%), cutoff (10%), and semi-cutoff (20%). (These definitions also include limits on light emitted above 90 degrees to reduce sky glow.)
Ordinances have also been written to limit the amount of light at the property line and beyond, but may be unrealistic or vague. Realistic limits and clarity in measurement need to be provided. Stating "zero light at the property line" is too vague. Absolute zero means that even if a light fixture is a mile away and the light source is visible, it is in violation, and would require hoods to be placed over every light fixture. What is realistic may vary according to whether an area is residential or industrial, urban, suburban or rural. The credit offered by LEED provides limits at the property line and 10-15 feet beyond it. At the 10-15 foot distance LEED limits light to 0.01 fc. (For comparison, a full moon provides 0.03 fc and a moonless night 0.004 fc). This is a very difficult limit to comply with while providing even light on a parking lot and driveway. How is the light to be measured? Horizontal measurements are common for interior and exterior lighting calculations. However, for light trespass the concern is how much light shines into a person's eye. Measurements may be made at approximate eye level (5' high) of the vertical light level facing into the site, or aimed at the brightest light source. Exceptions might be allowed where drives enter the street. This would permit street lights at the drive entrance to make cars more visible as they pull into traffic. Limiting pole height is another common ordinance tactic to reduce light trespass. This becomes counterproductive when the ordinance also has max:min ratios for safety concerns. Reducing pole height will increase dark spots on a site. Increasing the number of poles is only viable to a certain point due to the width of the aisles & parking. Otherwise poles would need to be placed in the parking spaces and aisles to maintain even lighting.
Over-illumination
Office building illuminated by high pressure sodium (HPS) lamps shining upward, of which much light goes into the sky and neighboring apartment blocks and causes light pollution. Location: Nijmegen, the Netherlands
Office building illuminated by high pressure sodium (HPS) lamps shining upward, of which much light goes into the sky and neighboring apartment blocks and causes light pollution. Location: Nijmegen, the Netherlands
Over-illumination is the excessive use of light. Specifically within the United States, over-illumination is responsible for approximately two million barrels of oil per day in energy wasted. This is based upon U.S. consumption of equivalent of 50 million barrels per day (7,900,000 m³/d) of petroleum.It is further noted in the same U.S. Department of Energy source that over 30 percent of all energy is consumed by commercial, industrial and residential sectors. Energy audits of existing buildings demonstrate that the lighting component of residential, commercial and industrial uses consumes about 20 to 40 percent of those land uses, variable with region and land use. (Residential use lighting consumes only 10 to 30 percent of the energy bill while commercial buildings major use is lighting.) Thus lighting energy accounts for about four or five million barrels of oil (equivalent) per day. Again energy audit data demonstrates that about 30 to 60 percent of energy consumed in lighting is unneeded or gratuitous.
An alternative calculation starts with the fact that commercial building lighting consumes in excess of 81.68 terawatts (1999 data) of electricity. according to the U.S. DOE. Thus commercial lighting alone consumes about four to five million barrels per day (equivalent) of petroleum, in line with the alternate rationale above to estimate U.S. lighting energy consumption.
Over-illumination stems from several factors:
* Not using timers, occupancy sensors or other controls to extinguish lighting when not needed
* Improper design, especially of workplace spaces, by specifying higher levels of light than needed for a given task
* Incorrect choice of fixtures or light bulbs, which do not direct light into areas as needed
* Improper selection of hardware to utilize more energy than needed to accomplish the lighting task
* Incomplete training of building managers and occupants to use lighting systems efficiently
* Inadequate lighting maintenance resulting in increased stray light and energy costs
* "Daylight lighting" can be required by citizens to reduce crime or by shop owners to attract customers, so over-illumination can be a design choice, not a fault. In both cases target achievement is questionable.
* Substitution of old mercury lamps with more efficient sodium or metal halide lamps using the same electrical power
* Indirect lighting techniques, such as lighting a vertical wall to bouce photons on the ground.
Most of these issues can be readily corrected with available, inexpensive technology; however, there is considerable inertia in the field of lighting design and with landlord/tenant practices that create barriers to rapid correction of these matters. Most importantly public awareness would need to improve for industrialized countries to realize the large payoff in reducing over-illumination
Glare
Glare is often the result of excessive contrast between bright and dark areas in the field of view. For example, glare can be associated with directly viewing the filament of an unshielded or badly shielded light. Light shining into the eyes of pedestrians and drivers can obscure night vision for up to an hour after exposure. Caused by high contrast between light and dark areas, glare can also make it difficult for the human eye to adjust to the differences in brightness. Glare is particularly an issue in road safety, as bright and/or badly shielded lights around roads may partially blind drivers or pedestrians unexpectedly, and contribute to accidents.
Glare can also result in reduced contrast, due to light scattering in the eye by excessive brightness, or to reflection of light from dark areas in the field of vision, with luminance similar to the background luminance. This kind of glare is a particular instance of disability glare, called veiling glare.
Glare can be categorized into different types. One such classification is described in a book by Bob Mizon, coordinator for the British Astronomical Association's Campaign for Dark Skies. According to this classification:
* Blinding Glare describes effects such as that caused by staring into the Sun. It is completely blinding and leaves temporary or permanent vision deficiencies.
* Disability Glare describes effects such as being blinded by an oncoming cars lights, or light scattering in fog or in the eye reduces contrast, as well as reflections from print and other dark areas that render them bright, with significant reduction in sight capabilities.
* Discomfort Glare does not typically cause a dangerous situation in itself, and is annoying and irritating at best. It can potentially cause fatigue if experienced over extended periods.
Clutter
Clutter refers to excessive groupings of lights. Groupings of lights may generate confusion, distract from obstacles (including those that they may be intended to illuminate), and potentially cause accidents. Clutter is particularly noticeable on roads where the street lights are badly designed, or where brightly lit advertising surrounds the roadways. Depending on the motives of the person or organization who installed the lights, their placement and design may even be intended to distract drivers, and can contribute to accidents. Clutter may also present a hazard in the aviation environment if aviation safety lighting must compete for pilot attention with non-relevant lighting. For instance, runway lighting may be confused with an array of suburban commercial lighting and aircraft collision avoidance lights may be confused with ground lights.
Sky glow
Sky glow refers to the "glow" effect that can be seen over populated areas. It is the combination of all light reflected from what it has illuminated escaping up into the sky and from all of the badly directed light in that area that also escapes into the sky, being scattered (redirected) by the atmosphere back toward the ground. This scattering is very strongly related to the wavelength of the light when the air is very clear (with very little aerosols). Rayleigh scattering dominates in such clear air, making the sky appear blue in the daytime. When there is significant aerosol (typical of most modern polluted conditions), the scattered light has less dependence on wavelength, making a whiter daytime sky. Because of this Rayleigh effect, and because of the eye's increased sensitivity to white or blue-rich light sources when adapted to very low light levels (see Purkinje effect), white or blue-rich light contributes significantly more to sky-glow than an equal amount of yellow light. Sky glow is of particular irritation to astronomers, because it reduces contrast in the night sky to the extent where it may even become impossible to see any but the brightest stars.
The Bortle Dark-Sky Scale, originally published in Sky & Telescope magazine, is sometimes used to quantify sky glow and general sky clarity. The Bortle Scale rates the darkness of the sky and the visibility of night sky phenomena such as the gegenschein and the zodiacal band, easily masked by sky glow, on a scale of one to nine, providing a detailed description of each step on the scale.
Light is particularly problematic for amateur astronomers, whose ability to observe the night sky from their property is likely to be inhibited by any stray light from nearby. Most major optical astronomical observatories are surrounded by zones of strictly-enforced restrictions on light emissions.
"Direct" sky glow can be reduced by selecting lighting fixtures which limit the amount of light emitted more than 90 degrees above the nadir. The IESNA definitions include full cutoff (0%), cutoff (2.5%), and semi-cutoff (5%). "Indirect" skyglow produced by reflections from vertical and horizontal surfaces is harder to manage; the only effective method for preventing it is by minimizing over-illumination.
Thursday, October 16, 2008
Noise pollution- Sources of noise- Human health effects- Mitigation and control of noise
Noise pollution (or environmental noise) is displeasing human- or machine-created sound that disrupts the activity or balance of human or animal life. A common form of noise pollution is from transportation, principally motor vehicles. The word "noise" comes from the Latin word nausea meaning "seasickness", referring originally to nuisance noise.
Sources of noise
The source of most noise worldwide is transportation systems, motor vehicle noise, but also including aircraft noise and rail noise. Poor urban planning may give rise to noise pollution, since side-by-side industrial and residential buildings can result in noise pollution in the residential area.
Other sources are car alarms, office equipment, factory machinery, construction work, grounds keeping equipment, barking dogs, appliances, power tools, lighting hum and audio entertainment systems.
Human health effects
Noise health effects are both health and behavioural in nature. The unwanted sound is called noise. This unwanted sound can damage physiological and psychological health. Noise pollution can cause annoyance and aggression, hypertension, high stress levels, tinnitus, hearing loss, sleep disturbances, and other harmful effects. Furthermore, stress and hypertension are the leading causes to health problems, whereas tinnitus can lead to forgetfulness, severe depression and at times panic attacks.
Chronic exposure to noise may cause noise-induced hearing loss. Older males exposed to significant occupational noise demonstrate significantly reduced hearing sensitivity than their non-exposed peers, though differences in hearing sensitivity decrease with time and the two groups are indistinguishable by age 79.[8] A comparison of Maaban tribesmen, who were insignificantly exposed to transportation or industrial noise, to a typical U.S. population showed that chronic exposure to moderately high levels of environmental noise contributes to hearing loss.
High noise levels can contribute to cardiovascular effects and exposure to moderately high levels during a single eight hour period causes a statistical rise in blood pressure of five to ten points and an increase in stress and vasoconstriction leading to the increased blood pressure noted above as well as to increased incidence of coronary artery disease.
Noise pollution is also a cause of annoyance. A 2005 study by Spanish researchers found that in urban areas households are willing to pay approximately four Euros per decibel per year for noise reduction.
Environmental effects
Noise can have a detrimental effect on animals by causing stress, increasing risk of mortality by changing the delicate balance in predator/prey detection and avoidance, and by interfering with their use of sounds in communication especially in relation to reproduction and in navigation. Acoustic overexposure can lead to temporary or permanent loss of hearing.
An impact of noise on animal life is the reduction of usable habitat that noisy areas may cause, which in the case of endangered species may be part of the path to extinction. One of the best known cases of damage caused by noise pollution is the death of certain species of beached whales, brought on by the loud sound of military sonar.
Noise also makes species communicate louder, which is called Lombard vocal response. Scientists and researchers have conducted experiments that show whales' song length is longer when submarine-detectors are on. If creatures don't "speak" loud enough, their voice will be masked by anthropogenic sounds. These unheard voices might be warnings, finding of prey, or preparations of net-bubbling. When one species begins speaking louder, it will mask other species' voice, causing the whole ecosystem to eventually speak louder.
Zebra finches become less faithful to their partners when exposed to traffic noise. This could alter a population's evolutionary trajectory by selecting traits, sapping resources normally devoted to other activities and thus lead to profound genetic and evolutionary consequences.
Mitigation and control of noise
Technology to mitigate or remove noise can be applied as follows:
There are a variety of strategies for mitigating roadway noise including: use of noise barriers, limitation of vehicle speeds, alteration of roadway surface texture, limitation of heavy duty vehicles, use of traffic controls that smooth vehicle flow to reduce braking and acceleration, and tyre design. An important factor in applying these strategies is a computer model for roadway noise, that is capable of addressing local topography, meteorology, traffic operations and hypothetical mitigation. Costs of building-in mitigation can be modest, provided these solutions are sought in the planning stage of a roadway project.
Aircraft noise can be reduced to some extent by design of quieter jet engines, which was pursued vigorously in the 1970s and 1980s. This strategy has brought limited but noticeable reduction of urban sound levels. Reconsideration of operations, such as altering flight paths and time of day runway use, have demonstrated benefits for residential populations near airports. FAA sponsored residential retrofit (insulation) programs initiated in the 1970s has also enjoyed success in reducing interior residential noise in thousands of residences across the United States.
Exposure of workers to Industrial noise has been addressed since the 1930s. Changes include redesign of industrial equipment, shock mounting assemblies and physical barriers in the workplace.
Legal status
Governments up until the 1970s viewed noise as a "nuisance" rather than an environmental problem. In the United States there are federal standards for highway and aircraft noise; states and local governments typically have very specific statutes on building codes, urban planning and roadway development. In Canada and the EU there are few national, provincial, or state laws that protect against noise.
Noise laws and ordinances vary widely among municipalities and indeed do not even exist in some cities. An ordinance may contain a general prohibition against making noise that is a nuisance, or it may set out specific guidelines for the level of noise allowable at certain times of the day and for certain activities.
Most city ordinances prohibit sound above a threshold intensity from trespassing over property line at night, typically between 10 p.m. and 6 a.m., and during the day restricts it to a higher sound level; however, enforcement is uneven. Many municipalities do not follow up on complaints. Even where a municipality has an enforcement office, it may only be willing to issue warnings, since taking offenders to court is expensive.
Many conflicts over noise pollution are handled by negotiation between the emitter and the receiver. Escalation procedures vary by country, and may include action in conjunction with local authorities, in particular the police. Noise pollution often persists because only five to ten percent of people affected by noise will lodge a formal complaint. Many people are not aware of their legal right to quiet and do not know how to register a complaint.
Sources of noise
The source of most noise worldwide is transportation systems, motor vehicle noise, but also including aircraft noise and rail noise. Poor urban planning may give rise to noise pollution, since side-by-side industrial and residential buildings can result in noise pollution in the residential area.
Other sources are car alarms, office equipment, factory machinery, construction work, grounds keeping equipment, barking dogs, appliances, power tools, lighting hum and audio entertainment systems.
Human health effects
Noise health effects are both health and behavioural in nature. The unwanted sound is called noise. This unwanted sound can damage physiological and psychological health. Noise pollution can cause annoyance and aggression, hypertension, high stress levels, tinnitus, hearing loss, sleep disturbances, and other harmful effects. Furthermore, stress and hypertension are the leading causes to health problems, whereas tinnitus can lead to forgetfulness, severe depression and at times panic attacks.
Chronic exposure to noise may cause noise-induced hearing loss. Older males exposed to significant occupational noise demonstrate significantly reduced hearing sensitivity than their non-exposed peers, though differences in hearing sensitivity decrease with time and the two groups are indistinguishable by age 79.[8] A comparison of Maaban tribesmen, who were insignificantly exposed to transportation or industrial noise, to a typical U.S. population showed that chronic exposure to moderately high levels of environmental noise contributes to hearing loss.
High noise levels can contribute to cardiovascular effects and exposure to moderately high levels during a single eight hour period causes a statistical rise in blood pressure of five to ten points and an increase in stress and vasoconstriction leading to the increased blood pressure noted above as well as to increased incidence of coronary artery disease.
Noise pollution is also a cause of annoyance. A 2005 study by Spanish researchers found that in urban areas households are willing to pay approximately four Euros per decibel per year for noise reduction.
Environmental effects
Noise can have a detrimental effect on animals by causing stress, increasing risk of mortality by changing the delicate balance in predator/prey detection and avoidance, and by interfering with their use of sounds in communication especially in relation to reproduction and in navigation. Acoustic overexposure can lead to temporary or permanent loss of hearing.
An impact of noise on animal life is the reduction of usable habitat that noisy areas may cause, which in the case of endangered species may be part of the path to extinction. One of the best known cases of damage caused by noise pollution is the death of certain species of beached whales, brought on by the loud sound of military sonar.
Noise also makes species communicate louder, which is called Lombard vocal response. Scientists and researchers have conducted experiments that show whales' song length is longer when submarine-detectors are on. If creatures don't "speak" loud enough, their voice will be masked by anthropogenic sounds. These unheard voices might be warnings, finding of prey, or preparations of net-bubbling. When one species begins speaking louder, it will mask other species' voice, causing the whole ecosystem to eventually speak louder.
Zebra finches become less faithful to their partners when exposed to traffic noise. This could alter a population's evolutionary trajectory by selecting traits, sapping resources normally devoted to other activities and thus lead to profound genetic and evolutionary consequences.
Mitigation and control of noise
Technology to mitigate or remove noise can be applied as follows:
There are a variety of strategies for mitigating roadway noise including: use of noise barriers, limitation of vehicle speeds, alteration of roadway surface texture, limitation of heavy duty vehicles, use of traffic controls that smooth vehicle flow to reduce braking and acceleration, and tyre design. An important factor in applying these strategies is a computer model for roadway noise, that is capable of addressing local topography, meteorology, traffic operations and hypothetical mitigation. Costs of building-in mitigation can be modest, provided these solutions are sought in the planning stage of a roadway project.
Aircraft noise can be reduced to some extent by design of quieter jet engines, which was pursued vigorously in the 1970s and 1980s. This strategy has brought limited but noticeable reduction of urban sound levels. Reconsideration of operations, such as altering flight paths and time of day runway use, have demonstrated benefits for residential populations near airports. FAA sponsored residential retrofit (insulation) programs initiated in the 1970s has also enjoyed success in reducing interior residential noise in thousands of residences across the United States.
Exposure of workers to Industrial noise has been addressed since the 1930s. Changes include redesign of industrial equipment, shock mounting assemblies and physical barriers in the workplace.
Legal status
Governments up until the 1970s viewed noise as a "nuisance" rather than an environmental problem. In the United States there are federal standards for highway and aircraft noise; states and local governments typically have very specific statutes on building codes, urban planning and roadway development. In Canada and the EU there are few national, provincial, or state laws that protect against noise.
Noise laws and ordinances vary widely among municipalities and indeed do not even exist in some cities. An ordinance may contain a general prohibition against making noise that is a nuisance, or it may set out specific guidelines for the level of noise allowable at certain times of the day and for certain activities.
Most city ordinances prohibit sound above a threshold intensity from trespassing over property line at night, typically between 10 p.m. and 6 a.m., and during the day restricts it to a higher sound level; however, enforcement is uneven. Many municipalities do not follow up on complaints. Even where a municipality has an enforcement office, it may only be willing to issue warnings, since taking offenders to court is expensive.
Many conflicts over noise pollution are handled by negotiation between the emitter and the receiver. Escalation procedures vary by country, and may include action in conjunction with local authorities, in particular the police. Noise pollution often persists because only five to ten percent of people affected by noise will lodge a formal complaint. Many people are not aware of their legal right to quiet and do not know how to register a complaint.
Saturday, October 11, 2008
Land pollution
Land pollution is the degradation of earth's land surfaces often caused by human activities and their misuse of land resources. Haphazard disposal of urban and industrial wastes, exploitation of minerals, and improper use of soil by inadequate agricultural practices are a few factors. Urbanization and industrialisation are major causes of land pollution.
The Industrial Revolution set a series of events into motion which destroyed natural habitats and polluted the environment, causing diseases in both humans and animals.
Increased mechanization
In some areas, metal ores are extracted from the ground, melted, cast and cooled using river water, which raises the temperature of water in rivers. This reduces the oxygen carrying capacity of the water and affects the aquatic life forms. The excavation of minerals leads to a large scale quarrying and defacing of land. To a large extent, this has been stopped or is more controlled, and attempts have been made to use the quarries profitably e.g. sand pits have been turned into boating lochs and some have been used as landfills. Central Scotland bears the scars of years of coal mining, with pit binges and slag heaps visible from the motorways.
The increase in the concentration of population in cities, along with the internal combustion engine, led to the increased number of roads and all the infra structure that goes with them. Roads cause visual, noise, light, air and water pollution, in addition to land pollution. The visual and noise areas are obvious, however light pollution is becoming more widely recognised as a problem. From outer space, large cities can be picked out at night by the glow of their lighting, so city dwellers seldom experience total darkness.
The contribution of vehicular traffic to air pollution is dealt with in another article, but, suffice to say that sulfur dioxide, nitrogen oxide and carbon monoxide are the main culprits. Water pollution is caused by the run off from roads of oil, salt and rubber residue, which enter the water courses and may make conditions unsuitable for certain organisms to live.
Agricultural effects
Increased agricultural land and field size
As the demand for food has grown very high, there is an increase in field size and mechanization. The increase in field size makes it economically viable for the farmer but results in loss of habitat and shelter for wildlife, as hedgerows and copses disappear. When crops are harvested, the naked soil is left open to wind after the heavy machinery has compacted it. Another consequence of more intensive agriculture is the move to monoculture. This is unnatural, it depletes the soil of nutrients, allows diseases and pests to spread and, in short, brings into play the use of chemical substances foreign to the environment.
Pesticides
Pesticides are chemicals used to kill pests. These can cause soil contamination and water contamination as well.pesticides are the chemical used for spaying t0 the crop. it kills the isects near by the crop which affects the crop. the biggest drawback of the pesticide is that that after a certain period of time the fertility of land goes away.
Herbicides
Herbicides are used to kill weeds, especially on pavements and railways. They are similar to auxins and most are biodegradable by soil bacteria. However one group derived from trinitrophenol (2:4 D and 2:4:5 T) have the impurity dioxin, which is very toxic and causes fatality even in low concentrations. It also causes spontaneous abortions, haemorrhaging and cancer. Agent Orange (50% 2:4:5 T) was used as a defoliant in Vietnam. Eleven million gallons were used and children born since then to American soldiers who served in this conflict, have shown increased physical and mental disabilities compared to the rest of the population. It affects the head of the sperm and the chromosomes inside it.
Another herbicide, much loved by murder story writers, is Paraquat. It is highly toxic but it rapidly degrades in soil due to the action of bacteria and does not kill soil fauna.
Fungicides
Fungicides are the group used to stop the growth of smuts and rusts on cereals, and mildews and moulds like Mucor on plants. The problem is that they may contain copper and mercury. Copper is very toxic (at 1ppm) to water plants and fish, and can enter human skin if sprayed and accumulate in the central nervous system. Organomercury compounds have been used to get rid of sedges, which are insidious and difficult to remove. However it also can accumulate in birds’ central nervous systems and kill them.
Insecticides
Insecticides are used to rid farms of pests which damage crops. The insects damage not only standing crops but also stored ones and in the tropics it is reckoned that one third of the total production is lost during food storage. As with fungicides, the first insecticides used in the nineteenth century were inorganic e.g. Paris Green and other compounds of arsenic. Nicotine has also been used since the late eighteenth century. There are now two main groups of synthetic insecticides -
Organochlorines
Organochlorines include DDT, Aldrin, Dieldrin and BHC. They are cheap to produce, potent and persistent. DDT was used on a massive scale from the 1930s, with a peak of 72,000 tonnes used 1970. Then usage fell as the harmful environmental effects were realized. It was found worldwide in fish and birds and was even discovered in the snow in the Antarctic. It is only slightly soluble in water but is very soluble in the bloodstream. It affects the nervous and endocrine systems and causes the eggshells of birds to lack calcium causing them to be easily breakable. It is thought to be responsible for the decline of the numbers of birds of prey like ospreys and peregrine falcons in the 1950s - they are now recovering.
As well as increased concentration via the food chain, it is known to enter via permeable membranes, so fish get it through their gills. As it has low water solubility, it tends to stay at the water surface, so organisms that live there are most affected. DDT found in fish that formed part of the human food chain caused concern, but the levels found in the liver, kidney and brain tissues was less than 1ppm and in fat was 10 ppm which was below the level likely to cause harm. However, DDT was banned in Britain and America to stop the further build up of it in the food chain. The USA exploited this ban and sold DDT to developing countries, who could not afford the expensive replacement chemicals and who did not have such stringent regulations governing the use of pesticides.
Some insects have developed a resistance to insecticides - e.g. the Anopheles mosquito which carries malaria.
Organophosphates
Organophosphates, e.g. parathion, methyl parathion and about 40 other insecticides are available nationally. Parathion is highly toxic, methyl-parathion is less so and Malathion is generally considered safe as it has low toxicity and is rapidly broken down in the mammalian liver. This group works by preventing normal nerve transmission as cholinesterase is prevented from breaking down the transmitter substance acetylcholine, resulting in uncontrolled muscle movements.
Entry of a variety of pesticides into our water supplies causes concern to environmental groups, as in many cases the long term effects of these specific chemicals is not known.
Restrictions came into force in July 1985 and were so frequently broken that in 1987, formal proceedings were taken against the British government. Britain is still the only European state to use Aldrin and organochlorines, although it was supposed to stop in 1993. East Anglia has the worst record for pesticide contamination of drinking water. Of the 350 pesticides used in Britain, only 50 can be analyzed, which is worrying for the global community.
Burial
Burial is the technique used by Jews, Muslims, Christians and other religions with Abrahamic influence, to dispose off the corpse of dead humans and animals. This process leads to regular soil erosion due to loosening of soil. Also, the decomposing fluids act as poisonous herbicides, pesticides and may even lead to epidemics in surrounding areas. It leads to soil pollution, soil erosion and even water pollution.
Increased waste disposal
In Scotland in 1993, 14 million tons of waste was produced. 100,000 tons was special waste and 260,000 tons was controlled waste from other parts of Britain and abroad. 45% of the special waste was in liquid form and 18% was asbestos - radioactive waste was not included. Of the controlled waste, 48% came from the demolition of buildings, 22% from industry, 17% from households and 13% from business - only 3% were recycled. 90% of controlled waste was buried in landfill sites and produced 2 million tons of methane gas. 1.5% was burned in incinerators and 1.5% were exported to be disposed of or recycled. There are 748 disposal sites in Scotland.
Landfills produce leachate, which has to be recycled to keep favourable conditions for microbial activity, methane gas and some carbon dioxide.
There are very few vacant or derelict land sites in the north east of Scotland, as there are few traditional heavy industries or coal/mineral extraction sites. However some areas are contaminated by aromatic hydrocarbons (500 cubic meters).
The Urban Waste Water Treatment Directive allows sewage sludge to be sprayed onto land and the volume is expected to double to 185,000 tons of dry solids in 2005. This has good agricultural properties due to the high nitrogen and phosphate content. In 1990/1991, 13% wet weight was sprayed onto 0.13% of the land , however this is expected to rise 15 fold by 2005. There is a need to control this so that pathogenic microorganisms do not get into water courses and to ensure that there is no accumulation of heavy metals in the top soil.
Increased wealth
At the end of twentieth century, people had even more leisure time and available wealth. This means that people can travel more often, increasing the number of cars on the roads. This is related to the increased litter problem in the countryside. This includes packaging, cans, bottles, etc. from picnics, but increasingly people are dumping household rubbish in the countryside instead of taking it to the local dump. Aesthetically, litter is unpleasant but poses threats to the wildlife through razor sharp glass that can be trodden on, plastic bags that can be eaten and choked on, etc. More and more litter is becoming a problem, especially in the more remote areas, which are now more accessible to the general public. Until the public takes responsibility to stop littering, legislation will have little effect and information and education will be the fore runners in the fight against the litter bugs.
The Industrial Revolution set a series of events into motion which destroyed natural habitats and polluted the environment, causing diseases in both humans and animals.
Increased mechanization
In some areas, metal ores are extracted from the ground, melted, cast and cooled using river water, which raises the temperature of water in rivers. This reduces the oxygen carrying capacity of the water and affects the aquatic life forms. The excavation of minerals leads to a large scale quarrying and defacing of land. To a large extent, this has been stopped or is more controlled, and attempts have been made to use the quarries profitably e.g. sand pits have been turned into boating lochs and some have been used as landfills. Central Scotland bears the scars of years of coal mining, with pit binges and slag heaps visible from the motorways.
The increase in the concentration of population in cities, along with the internal combustion engine, led to the increased number of roads and all the infra structure that goes with them. Roads cause visual, noise, light, air and water pollution, in addition to land pollution. The visual and noise areas are obvious, however light pollution is becoming more widely recognised as a problem. From outer space, large cities can be picked out at night by the glow of their lighting, so city dwellers seldom experience total darkness.
The contribution of vehicular traffic to air pollution is dealt with in another article, but, suffice to say that sulfur dioxide, nitrogen oxide and carbon monoxide are the main culprits. Water pollution is caused by the run off from roads of oil, salt and rubber residue, which enter the water courses and may make conditions unsuitable for certain organisms to live.
Agricultural effects
Increased agricultural land and field size
As the demand for food has grown very high, there is an increase in field size and mechanization. The increase in field size makes it economically viable for the farmer but results in loss of habitat and shelter for wildlife, as hedgerows and copses disappear. When crops are harvested, the naked soil is left open to wind after the heavy machinery has compacted it. Another consequence of more intensive agriculture is the move to monoculture. This is unnatural, it depletes the soil of nutrients, allows diseases and pests to spread and, in short, brings into play the use of chemical substances foreign to the environment.
Pesticides
Pesticides are chemicals used to kill pests. These can cause soil contamination and water contamination as well.pesticides are the chemical used for spaying t0 the crop. it kills the isects near by the crop which affects the crop. the biggest drawback of the pesticide is that that after a certain period of time the fertility of land goes away.
Herbicides
Herbicides are used to kill weeds, especially on pavements and railways. They are similar to auxins and most are biodegradable by soil bacteria. However one group derived from trinitrophenol (2:4 D and 2:4:5 T) have the impurity dioxin, which is very toxic and causes fatality even in low concentrations. It also causes spontaneous abortions, haemorrhaging and cancer. Agent Orange (50% 2:4:5 T) was used as a defoliant in Vietnam. Eleven million gallons were used and children born since then to American soldiers who served in this conflict, have shown increased physical and mental disabilities compared to the rest of the population. It affects the head of the sperm and the chromosomes inside it.
Another herbicide, much loved by murder story writers, is Paraquat. It is highly toxic but it rapidly degrades in soil due to the action of bacteria and does not kill soil fauna.
Fungicides
Fungicides are the group used to stop the growth of smuts and rusts on cereals, and mildews and moulds like Mucor on plants. The problem is that they may contain copper and mercury. Copper is very toxic (at 1ppm) to water plants and fish, and can enter human skin if sprayed and accumulate in the central nervous system. Organomercury compounds have been used to get rid of sedges, which are insidious and difficult to remove. However it also can accumulate in birds’ central nervous systems and kill them.
Insecticides
Insecticides are used to rid farms of pests which damage crops. The insects damage not only standing crops but also stored ones and in the tropics it is reckoned that one third of the total production is lost during food storage. As with fungicides, the first insecticides used in the nineteenth century were inorganic e.g. Paris Green and other compounds of arsenic. Nicotine has also been used since the late eighteenth century. There are now two main groups of synthetic insecticides -
Organochlorines
Organochlorines include DDT, Aldrin, Dieldrin and BHC. They are cheap to produce, potent and persistent. DDT was used on a massive scale from the 1930s, with a peak of 72,000 tonnes used 1970. Then usage fell as the harmful environmental effects were realized. It was found worldwide in fish and birds and was even discovered in the snow in the Antarctic. It is only slightly soluble in water but is very soluble in the bloodstream. It affects the nervous and endocrine systems and causes the eggshells of birds to lack calcium causing them to be easily breakable. It is thought to be responsible for the decline of the numbers of birds of prey like ospreys and peregrine falcons in the 1950s - they are now recovering.
As well as increased concentration via the food chain, it is known to enter via permeable membranes, so fish get it through their gills. As it has low water solubility, it tends to stay at the water surface, so organisms that live there are most affected. DDT found in fish that formed part of the human food chain caused concern, but the levels found in the liver, kidney and brain tissues was less than 1ppm and in fat was 10 ppm which was below the level likely to cause harm. However, DDT was banned in Britain and America to stop the further build up of it in the food chain. The USA exploited this ban and sold DDT to developing countries, who could not afford the expensive replacement chemicals and who did not have such stringent regulations governing the use of pesticides.
Some insects have developed a resistance to insecticides - e.g. the Anopheles mosquito which carries malaria.
Organophosphates
Organophosphates, e.g. parathion, methyl parathion and about 40 other insecticides are available nationally. Parathion is highly toxic, methyl-parathion is less so and Malathion is generally considered safe as it has low toxicity and is rapidly broken down in the mammalian liver. This group works by preventing normal nerve transmission as cholinesterase is prevented from breaking down the transmitter substance acetylcholine, resulting in uncontrolled muscle movements.
Entry of a variety of pesticides into our water supplies causes concern to environmental groups, as in many cases the long term effects of these specific chemicals is not known.
Restrictions came into force in July 1985 and were so frequently broken that in 1987, formal proceedings were taken against the British government. Britain is still the only European state to use Aldrin and organochlorines, although it was supposed to stop in 1993. East Anglia has the worst record for pesticide contamination of drinking water. Of the 350 pesticides used in Britain, only 50 can be analyzed, which is worrying for the global community.
Burial
Burial is the technique used by Jews, Muslims, Christians and other religions with Abrahamic influence, to dispose off the corpse of dead humans and animals. This process leads to regular soil erosion due to loosening of soil. Also, the decomposing fluids act as poisonous herbicides, pesticides and may even lead to epidemics in surrounding areas. It leads to soil pollution, soil erosion and even water pollution.
Increased waste disposal
In Scotland in 1993, 14 million tons of waste was produced. 100,000 tons was special waste and 260,000 tons was controlled waste from other parts of Britain and abroad. 45% of the special waste was in liquid form and 18% was asbestos - radioactive waste was not included. Of the controlled waste, 48% came from the demolition of buildings, 22% from industry, 17% from households and 13% from business - only 3% were recycled. 90% of controlled waste was buried in landfill sites and produced 2 million tons of methane gas. 1.5% was burned in incinerators and 1.5% were exported to be disposed of or recycled. There are 748 disposal sites in Scotland.
Landfills produce leachate, which has to be recycled to keep favourable conditions for microbial activity, methane gas and some carbon dioxide.
There are very few vacant or derelict land sites in the north east of Scotland, as there are few traditional heavy industries or coal/mineral extraction sites. However some areas are contaminated by aromatic hydrocarbons (500 cubic meters).
The Urban Waste Water Treatment Directive allows sewage sludge to be sprayed onto land and the volume is expected to double to 185,000 tons of dry solids in 2005. This has good agricultural properties due to the high nitrogen and phosphate content. In 1990/1991, 13% wet weight was sprayed onto 0.13% of the land , however this is expected to rise 15 fold by 2005. There is a need to control this so that pathogenic microorganisms do not get into water courses and to ensure that there is no accumulation of heavy metals in the top soil.
Increased wealth
At the end of twentieth century, people had even more leisure time and available wealth. This means that people can travel more often, increasing the number of cars on the roads. This is related to the increased litter problem in the countryside. This includes packaging, cans, bottles, etc. from picnics, but increasingly people are dumping household rubbish in the countryside instead of taking it to the local dump. Aesthetically, litter is unpleasant but poses threats to the wildlife through razor sharp glass that can be trodden on, plastic bags that can be eaten and choked on, etc. More and more litter is becoming a problem, especially in the more remote areas, which are now more accessible to the general public. Until the public takes responsibility to stop littering, legislation will have little effect and information and education will be the fore runners in the fight against the litter bugs.
Desertification- Prehistoric patterns-Countering desertification
Desertification is the degradation of land in arid and dry sub-humid areas, resulting primarily from human activities and influenced by climatic variations. A major impact of desertification is biodiversity loss and loss of productive capacity, for example, by transition from land dominated by shrublands to non-native grasslands. In the semi-arid regions of southern California, many coastal sage scrub and chaparral ecosystems have been replaced by non-native, invasive grasses due to the shortening of fire return intervals. This can create a monoculture of annual grass that can not support the wide range of animals once found in the original ecosystem. In Madagascar's central highland plateau, 10% of the entire country has been lost to desertification due to slash and burn agriculture by indigenous peoples. In Africa, if current trends of soil degradation continue, the continent might be able to feed just 25% of its population by 2025, according to UNU's Ghana-based Institute for Natural Resources in Africa.
Causes
Landsat image of sand dunes advancing on Nouakchott, the capital of Mauritania.
Landsat image of sand dunes advancing on Nouakchott, the capital of Mauritania.
Desertification is induced by several factors, primarily anthropogenic beginning in the Holocene era. The primary reasons for desertification are overgrazing, over cultivation, increased fire frequency, water impoundment, deforestation, overdrafting of groundwater, increased soil salinity, and global climate change.
Deserts may be separated from surrounding, less arid areas by mountains and other contrasting landforms that reflect fundamental structural differences in the terrain. In other areas, desert fringes form a gradual transition from a dry to a more humid environment, making it more subtle to determine the desert border. These transition zones can have fragile, delicately balanced ecosystems. Desert fringes often are a mosaic of microclimates. Small hollows support vegetation that picks up heat from the hot winds and protects the land from the prevailing winds. After rainfall the vegetated areas are distinctly cooler than the surroundings.
In these marginal areas human activity may stress the ecosystem beyond its tolerance limit, resulting in degradation of the land. By pounding the soil with their hooves, livestock compact the substrate, increase the proportion of fine material, and reduce the percolation rate of the soil, thus encouraging erosion by wind and water. Grazing and collection of firewood reduce or eliminate plants that bind the soil and prevent erosion. All these come about due to the trend towards settling in one area instead of a nomadic culture.
Sand dunes can encroach on human habitats. Sand dunes move through a few different means, all of them assisted by wind. One way that dunes can move is through saltation, where sand particles skip along the ground like a rock thrown across a pond might skip across the water's surface. When these skipping particles land, they may knock into other particles and cause them to skip as well. With slightly stronger winds, particles collide in mid-air, causing sheet flows. In a major dust storm, dunes may move tens of meters through such sheet flows. And like snow, sand avalanches, falling down the steep slopes of the dunes that face away from the winds, also moving the dunes forward.
It is a common misconception that droughts by themselves cause desertification. While drought is a contributing factor, the root causes are all related to man's overexploitation of the environment.[citation needed] There is no geological evidence that deserts expanded significantly before the advent of civilization. Droughts are common in arid and semiarid lands, and well-managed lands can recover from drought when the rains return. Continued land abuse during droughts, however, increases land degradation. Increased population and livestock pressure on marginal lands has accelerated desertification. In some areas, nomads moving to less arid areas disrupt the local ecosystem and increase the rate of erosion of the land. Nomads typically try to escape the desert, but because of their land-use practices, they are bringing the desert with them.
Some arid and semi-arid lands can support crops, but additional pressure from greater populations or decreases in rainfall can lead to the few plants present disappearing. The soil becomes exposed to wind, causing soil particles to be deposited elsewhere. The top layer becomes eroded. With the removal of shade, rates of evaporation increase and salts become drawn up to the surface. This increases soil salinity which inhibits plant growth. The loss of plants causes less moisture to be retained in the area, which may change the climate pattern leading to lower rainfall.
This degradation of formerly productive land is a complex process. It involves multiple causes, and it proceeds at varying rates in different climates. Desertification may intensify a general climatic trend toward greater aridity, or it may initiate a change in local climate. Desertification does not occur in linear, easily mappable patterns. Deserts advance erratically, forming patches on their borders. Areas far from natural deserts can degrade quickly to barren soil, rock, or sand through poor land management. The presence of a nearby desert has no direct relationship to desertification. Unfortunately, an area undergoing desertification is brought to public attention only after the process is well under way. Often little data are available to indicate the previous state of the ecosystem or the rate of degradation.
Combating desertification is complex and difficult, usually impossible without alteration of land management practises that led to the desertification. Over-exploitation of the land and climate variations can have identical impacts and be connected in feedbacks, which makes it very difficult to choose the right mitigation strategy. Investigating the historic desertification plays a special role since it allows better distinguishing of human and natural factors. In this context, recent research about historic desertification in Jordan questions the dominant role of man. It seems possible that current measures like reforestation projects cannot achieve their goals if global warming continues. Forests may die when it gets drier, and more frequent extreme events as testified in sediments from earlier periods could become a threat for agriculture, water supply, and infrastructure.
Prehistoric patterns
Desertification is a historic phenomenon; the world's great deserts were formed by natural processes interacting over long intervals of time. During most of these times, deserts have grown and shrunk independent of human activities. Paleodeserts are large sand seas now inactive because they are stabilized by vegetation, some extending beyond the present margins of core deserts, such as the Sahara. Many deserts in western Asia arose because of an overpopulation of prehistoric species and subspecies during the late Cretaceous era.
Dated fossil pollen indicates that today's Sahara desert has been changing between desert and fertile savanna. Studies also show that prehistorically the advance and retreat of deserts tracked yearly rainfall, whereas a pattern of increasing amounts of desert began with human-driven activities of overgrazing and deforestation.
A chief difference of prehistoric versus present desertification is the much greater rate of desertification than in prehistoric and geologic time scales, due to anthropogenic influences.
Historical and current desertification
Overgrazing and to a lesser extent drought in the 1930s transformed parts of the Great Plains in the United States into the "Dust Bowl". During that time, a considerable fraction of the plains population abandoned their homes to escape the unproductive lands. Improved agricultural and water management have prevented a disaster of the earlier magnitude from recurring, but desertification presently affects tens of millions of people with primary occurrence in the lesser developed countries.
Lake Chad in a 2001 satellite image, with the actual lake in blue. The lake has shrunk by 95% since the 1960s.
Lake Chad in a 2001 satellite image, with the actual lake in blue. The lake has shrunk by 95% since the 1960s.
Desertification is widespread in many areas of the People's Republic of China. The populations of rural areas have increased since 1949 for political reasons as more people have settled there. While there has been an increase in livestock, the land available for grazing has decreased. Also the importing of European cattle such as Friesian and Simmental, which have higher food intakes, has made things worse.
Human overpopulation is leading to destruction of tropical wet forests and tropical dry forests, due to widening practices of slash-and-burn and other methods of subsistence farming necessitated by famines in lesser developed countries. A sequel to the deforestation is typically large scale erosion, loss of soil nutrients and sometimes total desertification. Examples of this extreme outcome can be seen on Madagascar's central highland plateau, where about seven percent of the country's total land mass has become barren, sterile land.
Overgrazing has made the Rio Puerco Basin of central New Mexico one of the most eroded river basins of the western United States and has increased the high sediment content of the river. Overgrazing is also an issue with some regions of South Africa such as the Waterberg Massif, although restoration of native habitat and game has been pursued vigorously since about 1980.
Another example of desertification occurring is in the Sahel. The chief cause of desertification in the Sahel is slash-and-burn farming practised by an expanding human population. The Sahara is expanding south at an average rate of 30 miles per year.
The Desert of Maine is a 40 acre dune of glacial silt near Freeport, Maine. Overgrazing and soil erosion exposed the cap of the dune, revealing the desert as a small patch that continued to grow, overtaking the land. The site is maintained as a tourist attraction.
Ghana and Nigeria currently experience desertification; in the latter, desertification overtakes about 1,355 square miles (3,510 km2) of land per year. The Central Asian countries, Kazakhstan, Kyrgyzstan, Mongolia, Tajikistan, Turkmenistan, and Uzbekistan, are also affected. More than 80% of Afghanistan's and Pakistan's land could be subject to soil erosion and desertification. In Kazakhstan, nearly half of the cropland has been abandoned since 1980. In Iran, sand storms were said to have buried 124 villages in Sistan and Baluchestan Province in 2002, and they had to be abandoned. In Latin America, Mexico and Brazil are affected by desertification.
Countering desertification
Desertification has been recognized as a major threat to biodiversity. Numerous countries have developed Biodiversity Action Plans to counter its effects, particularly in relation to the protection of endangered flora and fauna.
A number of solutions have been tried in order to reduce the rate of desertification and regain lost land; however, most measures treat symptoms of sand movement and do not address the root causes of land modification such as overgrazing and unsustainable farming. Leguminous plants, which extracts nitrogen from the air and fixes it in the soil, can be planted to restore fertility. Stones stacked around the base of trees collect morning dew and help retain soil moisture. Artificial grooves can be dug in the ground to retain rainfall and trap wind-blown seeds. In Iran, petroleum is being sprayed over semi-arid cropland. This coats seedlings to prevent moisture loss and stop them being blown away. Windbreaks made from trees and bushes to reduce soil erosion and evapotranspiration were widely encouraged by development agencies from the middle of the 1980s in the Sahel area of Africa.
In developing countries, with many local people using trees for firewood and cooking the problem has become acute. In order to gain further supplies of fuel the local population add more pressure to the depleted forests; adding to the desertification process. Solar ovens and efficient wood burning cook stoves are being advocated as a means to relieving some of this pressure upon the environment.
While desertification has received some publicity by the news media, most people are unaware of the extent of environmental degradation of productive lands and the expansion of deserts. In 1988 Ridley Nelson pointed out that desertification is a subtle and complex process of deterioration.
At the local level, individuals and governments can partially or temporarily forestall desertification. Sand fences are used throughout the Middle East and the US, in the same way snow fences are used in the north. Placement of straw grids, each up to a square meter in area, will also decrease the surface wind velocity. Shrubs and trees planted within the grids are protected by the straw until they take root. However, some studies suggest that planting of trees depletes water supplies in the area. In areas where some water is available for irrigation, shrubs planted on the lower one-third of a dune's windward side will stabilize the dune. This vegetation decreases the wind velocity near the base of the dune and prevents much of the sand from moving. Higher velocity winds at the top of the dune level it off and trees can be planted atop these flattened surfaces.
Oases and farmlands in windy regions can be protected by planting tree fences or grass belts. Sand that manages to pass through the grass belts can be caught in strips of trees planted as wind breaks 50 to 100 meters apart adjacent to the belts. Small plots of trees may also be scattered inside oases to stabilize the area. On a much larger scale, a "Green Wall of China", which will eventually stretch more than 5,700 kilometers in length, nearly as long as the Great Wall of China, is being planted in north-eastern China to protect "sandy lands" – deserts created by human activity.
Africa, with coordination from Senegal, has launched its own "green wall" project. Trees will be planted on a 15 km wide land strip from Senegal to Djibouti. Aside from countering desert progression, the project is also aimed at creating new economic activities, especially thanks to tree products such as gum arabic
More efficient use of existing water resources and control of salinization are other effective tools for improving arid lands. New ways are being sought to use surface-water resources such as rain water harvesting or irrigating with seasonal runoff from adjacent highlands. New ways are also being sought to find groundwater resources and to develop more effective ways of irrigating arid and semiarid lands. Research on the reclamation of deserts is also focusing on discovering proper crop rotation to protect the fragile soil, on understanding how sand-fixing plants can be adapted to local environments, and on how grazing lands and water resources can be developed effectively without being overused.
Causes
Landsat image of sand dunes advancing on Nouakchott, the capital of Mauritania.
Landsat image of sand dunes advancing on Nouakchott, the capital of Mauritania.
Desertification is induced by several factors, primarily anthropogenic beginning in the Holocene era. The primary reasons for desertification are overgrazing, over cultivation, increased fire frequency, water impoundment, deforestation, overdrafting of groundwater, increased soil salinity, and global climate change.
Deserts may be separated from surrounding, less arid areas by mountains and other contrasting landforms that reflect fundamental structural differences in the terrain. In other areas, desert fringes form a gradual transition from a dry to a more humid environment, making it more subtle to determine the desert border. These transition zones can have fragile, delicately balanced ecosystems. Desert fringes often are a mosaic of microclimates. Small hollows support vegetation that picks up heat from the hot winds and protects the land from the prevailing winds. After rainfall the vegetated areas are distinctly cooler than the surroundings.
In these marginal areas human activity may stress the ecosystem beyond its tolerance limit, resulting in degradation of the land. By pounding the soil with their hooves, livestock compact the substrate, increase the proportion of fine material, and reduce the percolation rate of the soil, thus encouraging erosion by wind and water. Grazing and collection of firewood reduce or eliminate plants that bind the soil and prevent erosion. All these come about due to the trend towards settling in one area instead of a nomadic culture.
Sand dunes can encroach on human habitats. Sand dunes move through a few different means, all of them assisted by wind. One way that dunes can move is through saltation, where sand particles skip along the ground like a rock thrown across a pond might skip across the water's surface. When these skipping particles land, they may knock into other particles and cause them to skip as well. With slightly stronger winds, particles collide in mid-air, causing sheet flows. In a major dust storm, dunes may move tens of meters through such sheet flows. And like snow, sand avalanches, falling down the steep slopes of the dunes that face away from the winds, also moving the dunes forward.
It is a common misconception that droughts by themselves cause desertification. While drought is a contributing factor, the root causes are all related to man's overexploitation of the environment.[citation needed] There is no geological evidence that deserts expanded significantly before the advent of civilization. Droughts are common in arid and semiarid lands, and well-managed lands can recover from drought when the rains return. Continued land abuse during droughts, however, increases land degradation. Increased population and livestock pressure on marginal lands has accelerated desertification. In some areas, nomads moving to less arid areas disrupt the local ecosystem and increase the rate of erosion of the land. Nomads typically try to escape the desert, but because of their land-use practices, they are bringing the desert with them.
Some arid and semi-arid lands can support crops, but additional pressure from greater populations or decreases in rainfall can lead to the few plants present disappearing. The soil becomes exposed to wind, causing soil particles to be deposited elsewhere. The top layer becomes eroded. With the removal of shade, rates of evaporation increase and salts become drawn up to the surface. This increases soil salinity which inhibits plant growth. The loss of plants causes less moisture to be retained in the area, which may change the climate pattern leading to lower rainfall.
This degradation of formerly productive land is a complex process. It involves multiple causes, and it proceeds at varying rates in different climates. Desertification may intensify a general climatic trend toward greater aridity, or it may initiate a change in local climate. Desertification does not occur in linear, easily mappable patterns. Deserts advance erratically, forming patches on their borders. Areas far from natural deserts can degrade quickly to barren soil, rock, or sand through poor land management. The presence of a nearby desert has no direct relationship to desertification. Unfortunately, an area undergoing desertification is brought to public attention only after the process is well under way. Often little data are available to indicate the previous state of the ecosystem or the rate of degradation.
Combating desertification is complex and difficult, usually impossible without alteration of land management practises that led to the desertification. Over-exploitation of the land and climate variations can have identical impacts and be connected in feedbacks, which makes it very difficult to choose the right mitigation strategy. Investigating the historic desertification plays a special role since it allows better distinguishing of human and natural factors. In this context, recent research about historic desertification in Jordan questions the dominant role of man. It seems possible that current measures like reforestation projects cannot achieve their goals if global warming continues. Forests may die when it gets drier, and more frequent extreme events as testified in sediments from earlier periods could become a threat for agriculture, water supply, and infrastructure.
Prehistoric patterns
Desertification is a historic phenomenon; the world's great deserts were formed by natural processes interacting over long intervals of time. During most of these times, deserts have grown and shrunk independent of human activities. Paleodeserts are large sand seas now inactive because they are stabilized by vegetation, some extending beyond the present margins of core deserts, such as the Sahara. Many deserts in western Asia arose because of an overpopulation of prehistoric species and subspecies during the late Cretaceous era.
Dated fossil pollen indicates that today's Sahara desert has been changing between desert and fertile savanna. Studies also show that prehistorically the advance and retreat of deserts tracked yearly rainfall, whereas a pattern of increasing amounts of desert began with human-driven activities of overgrazing and deforestation.
A chief difference of prehistoric versus present desertification is the much greater rate of desertification than in prehistoric and geologic time scales, due to anthropogenic influences.
Historical and current desertification
Overgrazing and to a lesser extent drought in the 1930s transformed parts of the Great Plains in the United States into the "Dust Bowl". During that time, a considerable fraction of the plains population abandoned their homes to escape the unproductive lands. Improved agricultural and water management have prevented a disaster of the earlier magnitude from recurring, but desertification presently affects tens of millions of people with primary occurrence in the lesser developed countries.
Lake Chad in a 2001 satellite image, with the actual lake in blue. The lake has shrunk by 95% since the 1960s.
Lake Chad in a 2001 satellite image, with the actual lake in blue. The lake has shrunk by 95% since the 1960s.
Desertification is widespread in many areas of the People's Republic of China. The populations of rural areas have increased since 1949 for political reasons as more people have settled there. While there has been an increase in livestock, the land available for grazing has decreased. Also the importing of European cattle such as Friesian and Simmental, which have higher food intakes, has made things worse.
Human overpopulation is leading to destruction of tropical wet forests and tropical dry forests, due to widening practices of slash-and-burn and other methods of subsistence farming necessitated by famines in lesser developed countries. A sequel to the deforestation is typically large scale erosion, loss of soil nutrients and sometimes total desertification. Examples of this extreme outcome can be seen on Madagascar's central highland plateau, where about seven percent of the country's total land mass has become barren, sterile land.
Overgrazing has made the Rio Puerco Basin of central New Mexico one of the most eroded river basins of the western United States and has increased the high sediment content of the river. Overgrazing is also an issue with some regions of South Africa such as the Waterberg Massif, although restoration of native habitat and game has been pursued vigorously since about 1980.
Another example of desertification occurring is in the Sahel. The chief cause of desertification in the Sahel is slash-and-burn farming practised by an expanding human population. The Sahara is expanding south at an average rate of 30 miles per year.
The Desert of Maine is a 40 acre dune of glacial silt near Freeport, Maine. Overgrazing and soil erosion exposed the cap of the dune, revealing the desert as a small patch that continued to grow, overtaking the land. The site is maintained as a tourist attraction.
Ghana and Nigeria currently experience desertification; in the latter, desertification overtakes about 1,355 square miles (3,510 km2) of land per year. The Central Asian countries, Kazakhstan, Kyrgyzstan, Mongolia, Tajikistan, Turkmenistan, and Uzbekistan, are also affected. More than 80% of Afghanistan's and Pakistan's land could be subject to soil erosion and desertification. In Kazakhstan, nearly half of the cropland has been abandoned since 1980. In Iran, sand storms were said to have buried 124 villages in Sistan and Baluchestan Province in 2002, and they had to be abandoned. In Latin America, Mexico and Brazil are affected by desertification.
Countering desertification
Desertification has been recognized as a major threat to biodiversity. Numerous countries have developed Biodiversity Action Plans to counter its effects, particularly in relation to the protection of endangered flora and fauna.
A number of solutions have been tried in order to reduce the rate of desertification and regain lost land; however, most measures treat symptoms of sand movement and do not address the root causes of land modification such as overgrazing and unsustainable farming. Leguminous plants, which extracts nitrogen from the air and fixes it in the soil, can be planted to restore fertility. Stones stacked around the base of trees collect morning dew and help retain soil moisture. Artificial grooves can be dug in the ground to retain rainfall and trap wind-blown seeds. In Iran, petroleum is being sprayed over semi-arid cropland. This coats seedlings to prevent moisture loss and stop them being blown away. Windbreaks made from trees and bushes to reduce soil erosion and evapotranspiration were widely encouraged by development agencies from the middle of the 1980s in the Sahel area of Africa.
In developing countries, with many local people using trees for firewood and cooking the problem has become acute. In order to gain further supplies of fuel the local population add more pressure to the depleted forests; adding to the desertification process. Solar ovens and efficient wood burning cook stoves are being advocated as a means to relieving some of this pressure upon the environment.
While desertification has received some publicity by the news media, most people are unaware of the extent of environmental degradation of productive lands and the expansion of deserts. In 1988 Ridley Nelson pointed out that desertification is a subtle and complex process of deterioration.
At the local level, individuals and governments can partially or temporarily forestall desertification. Sand fences are used throughout the Middle East and the US, in the same way snow fences are used in the north. Placement of straw grids, each up to a square meter in area, will also decrease the surface wind velocity. Shrubs and trees planted within the grids are protected by the straw until they take root. However, some studies suggest that planting of trees depletes water supplies in the area. In areas where some water is available for irrigation, shrubs planted on the lower one-third of a dune's windward side will stabilize the dune. This vegetation decreases the wind velocity near the base of the dune and prevents much of the sand from moving. Higher velocity winds at the top of the dune level it off and trees can be planted atop these flattened surfaces.
Oases and farmlands in windy regions can be protected by planting tree fences or grass belts. Sand that manages to pass through the grass belts can be caught in strips of trees planted as wind breaks 50 to 100 meters apart adjacent to the belts. Small plots of trees may also be scattered inside oases to stabilize the area. On a much larger scale, a "Green Wall of China", which will eventually stretch more than 5,700 kilometers in length, nearly as long as the Great Wall of China, is being planted in north-eastern China to protect "sandy lands" – deserts created by human activity.
Africa, with coordination from Senegal, has launched its own "green wall" project. Trees will be planted on a 15 km wide land strip from Senegal to Djibouti. Aside from countering desert progression, the project is also aimed at creating new economic activities, especially thanks to tree products such as gum arabic
More efficient use of existing water resources and control of salinization are other effective tools for improving arid lands. New ways are being sought to use surface-water resources such as rain water harvesting or irrigating with seasonal runoff from adjacent highlands. New ways are also being sought to find groundwater resources and to develop more effective ways of irrigating arid and semiarid lands. Research on the reclamation of deserts is also focusing on discovering proper crop rotation to protect the fragile soil, on understanding how sand-fixing plants can be adapted to local environments, and on how grazing lands and water resources can be developed effectively without being overused.
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