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Soil

Soil is the ultimate life support system. Every land based and some water based living organisms rely on soil for sustenance and general survival on the planet. Like most things on earth though soil is scarce and in recent times has been mistreated and degraded and the way in which we react to this critical issue may have a big bearing on our future on the planet. This article will take a brief look at the background and composition of soil, the problems it has faced and is currently facing, hazardous waste and contamination and possible remediation and mitigation strategies that could be applied going forward into the future.

Soil Formation

Soil contains a mix of particles which is made up from organic materials, air and water. This thin layer of soil on the surface of the planet is vital to support organisms and living creatures, and the top layer, which is called 'solum' is the life supporting layer, which is only around two metres in depth on average. Below this level is the subsoil, which is non organic and can range in depth from 1 metre to over 100 metres and is found above the bedrock. The solum and subsoil together is known as the soil mantle, and is capable of supporting terrestrial objects such as forests, lakes, roads or buildings. Soil is created by the weathering of the bedrock, and occurs extremely slowly at a rate of a fraction of a millimetre per year. The common inorganic mineral matrix of the soil is just one part of soil, as it also contains water, air, dissolved minerals (nutrients), organic matter and bacteria 1).

The bacteria that is present in soil breaks down organic matter and produces carbon dioxide, water and some types of acids. As organic matter is introduced to the soil mainly at the surface, and then broken down at many various depths, soils tend to have less organic matter contents the deeper you go. A soil that is good and can promote the healthy growth of plants has lots of air spaces in it so that the roots can breathe, and is also relatively easily deformable so that they can spread through the soil. A good soil also has abundant supplies of water and nutrients. Extremes of acidity can cause various nutrients to become tightly bound to the surface of inorganic soil particles, thereby making them hard or impossible to access. The pH of soil should be neutral to slightly acidic in order to achieve optimal conditions for plant growth. Aeration and the capacity to hold water are directly enhanced by the organic matter that is present in the soil, and polysaccharides and humic acids which are produced by bacteria when they break down organic matter cause fine particles in the soil to adhere to each other, thus increasing the coarseness and aeration capacity of the soil. The humic acids are effective buffers and tend to help to stabilise and moderate the pH levels. As plants are made of the nutrients which plants need to grow, decomposing plant material returns to the soil the nutrients which are needed to help support further plant growth. 2).

Taking all of this into consideration, organic materials are key for good soils. If the soil does not receive a return of nutrients in the form of organic matter, the soil will simply be incapable of supporting any type of plants, trees or other forms of life. This becomes critical in the topsoil, as this is were these nutrients are mainly located. Different types of soil are classified by three main characteristics, and they are composition, soil water and soil texture.

Composition

Composition is usually classed as either mineral or organic. In environments where decomposition is slow, such as in areas where water levels are very high such as swamps, marshes or wetlands, soil may consist of large amounts of particles that are organic in nature. Generally organic matter is a good source of nutrients for plants and the other important chemicals that are released from plant tissue as it decomposes. Where plant cover is reduced or completely lost from a site, the organic system of the can become unbalanced and may have a negative impact by creating a loss in soil fertility and interfering with nutrient recycling which is highly important to the ecosystem that originally was present at the site.

Soil Water

Soil water is critical to nearly all facets of soil. The water movement that occurs in the soil and the relevant processes of a chemical nature are responsible for the dissolution and precipitation of minerals and the weathering of the bedrock which is located beneath the soil. The amount of moisture in the soil can help to determine the organic make up of the topsoil, thus creating an ideal base from which plants, trees and other soil dependent living organisms can grow and thrive.

Soil Texture

The texture of soil is determined by the size of the particles of the soil. This can be done by taking the measurements of the average sizes in the soil samples, and these are usually divided into three different categories: Sand, silt and clay, with sand having the largest particles and clay having the smallest.

Erosion

Erosion is the process where soil, and in particular topsoil is lost due to movements by wind and water. Soil erosion is one of the biggest issues that is faced worldwide and poses a great threat to food stability and supply. The topsoil that is moved by water is called alluvium and this is responsible for much of the soil erosion that occurs worldwide. The soil that is moved by wind is called colluvium and this generally occurs in inland areas or areas close to deserts or arid locations. Whilst erosion has always existed on the planet, like most other things it has been increased and magnified by human activities and it is estimated that we lose 25 billion tonnes of topsoil per year globally 3).

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Soil Erosion in Peru 4)

Water erosion, or alluvium, usually occurs in three different ways: Gully erosion, sheet erosion and rill erosion. Gully erosion occurs mainly in farming areas and fields where deep gullies are formed after a major rain event and this creates a gravity assisted loss of soil, as more water causes the soil on the edge of the gully to fall in, expanding the size of the gully and this can keep going on whilst there is a flow of water present. Sheet erosion occurs when water flows down a hill in a uniform fashion, stripping the topsoil and all of the organic matter and moving it downhill, creating a large deposit at the bottom of the slope and depletion in the areas which it passed. Rill erosion occurs when water flow creates several small gully type formations and is generally seen in farms and crop fields. This works in a similar fashion to gully erosion, but on a smaller scale 5).

The reason we encounter higher levels of erosion is due to the removal of protective plants, trees and vegetation from soils that are at high risk of erosion. Generally soils with low clay contents are considered to be at high risk of erosion, due to the fact that they are not as tightly bound as clay rich soils. The presence of large rocks is also a good defence against erosion, as this can help to limit the movement of the topsoil to far areas. When the topsoil is lost, the soil loses the ability to harvest nutrients and also loses it's water holding capacity, which is vital for life. The movement of this topsoil and organic matter also plays a large part in water pollution, as the particles that are moved can settle in lakes, dams, rivers or out to sea which can severely affect the balance of these water bodies, potentially creating problems such as algal blooms 6)

Even though it is possible to renew topsoil, we must remember that the formation of topsoil has taken many millions of years, and to replace the soil it may take may thousands of years. Farming is not the only culprits in the loss of topsoils, mining, forestry and land development processes are also just as responsible for the loss. The most critical aspect is the removal of vegetation, and in order to combat this the vegetation that is removed must be kept at an absolute minimum.

Desertification

When large amounts of topsoil are lost, generally over 50 percent, it causes a condition called desertification. This is caused by erosion, overgrazing, over irrigating, mining, forestry or land development. Around 850 million hectares (approximately the size of Australia) has been lost to desertification in the past 60 years worldwide. The land is rendered useless and cannot grow anything, hence the title given. This figure increases by around 6 million hectares per year and is most prevalent in Sub-Saharan Africa, China, Pakistan, India and parts of the USA. The increase in population and the rise in demand for food, coupled with less farming land possibly spells out a recipe for disaster 7)

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Desertification in Brazil 8)

Contamination

Another factor that has a detrimental effect on soil is contamination. This contamination is usually caused by chemicals created by large industrial projects, herbicides and pesticides, atmospheric fallout or mining practices. Atmospheric fallout can occur in areas near where fossil fuels such as coal is burnt, increasing the amount of acidity, radioactivity and sulphur dioxide in the rain and cause it to settle on the topsoil. Mining activities can cause heavy metals which are usually locked up deep under the surface to be extracted and then mixed with water, which can cause deposits of these contaminants further upstream. Herbicides and pesticides that do not break down over a short period of time can also cause a buildup in the soil and eventually making it too contaminated to grow any type of crop, or causing the presence of the chemicals in the crops that are produced making it unfit for human or animal consumption 9)

Salinization

Salinization occurs due to over irrigation of the topsoil. More water that usual is pumped down channels which can help increase the yield of crops, however as per usual this also has a negative effect. When this water evaporates, it leaves deposits of whatever chemicals that it contains on top of the soil, such as salts like sodium, chloride, magnesium, sulphate and carbonate). As these salts continue to build up in the soil, this changes the pH balance and then hinders or completely stops the growth of any type of plant on the soil. If more water is used to flush the salt away, the excess water can be absorbed by the water table which causes it to rise and this in turn brings the salty water in the table to the surface, causing the area to be terminally salty and unusable. The amounts of land lost to salinization per year is staggering, with 500,000 hectares per year lost due to this process. The flushing process can also affect other things and areas, and can cause water pollution in lakes, rivers and waterways due to the excessive levels of salt. Salinization is not a new phenomenon, with evidence that it caused massive crop losses in 3,000bc in Mesopotamia, which is now known as the southern area of Iraq. This land is still unusable in most of this area even after thousands of years 10).

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Salinization in California

Hazardous Waste

Hazardous waste can be defined as any discarded liquid, solid or gas that causes a risk of harm to human health, animal health or the environment. There are a multitude of things that can be classified as hazardous waste, such as heavy metals, solvents, acids, CFC's, infectious wastes, herbicide, pesticides, batteries or radioactive material to name a few. Traditionally hazardous waste has been put into drums or other storage devices and buried deep in the ground. Unfortunately this process has been found to be unsuccessful, with many hazardous waste storage methods failing and causing massive contamination to the soils and the area in which is it located. There are two major problems that are being faced by authorities at present, firstly what to do with current contaminated sites and secondly what to do with future hazardous wastes. The currently contaminated sites are a big concern, as the previous methods that were used may be highly inadequate, requiring complete digging up, cleaning and replacement of the soil and also adding clay and water sources to keep the contaminants bound in the clay. Where possible bioremediation is used to break down the contaminants by using bacteria that breaks down the different chemicals into harmless micro organisms.

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Hazardous Waste

For future hazardous waste, there is now a greater knowledge of the contents and known half lives, however this does not make the solutions any easier. The burial method is still being used, but with containers that are stronger and more resistant over time. This unfortunately costs a great deal of money, and some less economically developed nations still burying hazardous waste using methods that are outdated and ineffective. What compounds this problem also is that first world countries will pay these countries to take their hazardous waste, hence concentrating these problems in one area, potentially creating a huge risk of an environmental catastrophe 11).

We are very limited in the ways in which we can get rid of hazardous waste or render it harmless. This can vary depending on the type of waste, but there has been progress in some areas by extracting certain contents of the waste which can then be used by other industries, finding substitute products that are less hazardous, incineration or by placing limits on the amounts of waste that can be produced by each company. All of these solutions are not without their problems however, and they can be very energy intensive and highly costly. Recently a high combustion incinerator has been invented that burns at temperatures in excess of 10,000 degrees Celsius and can incinerate 99.99% of all toxins. This process however costs around $100 per kilogram of material burnt, and is ineffective against hazardous wastes such as heavy metals and radioactive waste, which we simply cannot get rid of 12). Unfortunately economists and governments do not calculate the real economic price of land use and hazardous waste, and we continue to spiral towards a critical point at which it no longer becomes possible to grow food or store waste.

Conclusion

Soil is critical for most life on this planet. We are currently depleting our soil at alarming rates and whilst there is some progress being made in the means of new techniques, we are still losing far too much of our topsoils and contaminating our land that is unsustainable. More effort needs to be made in order to alter farming and agricultural methods to stop the loss and erosion of vital life giving soil, and ensuring that we have viable, long term food security. The continued contamination of soils also reduces the amount of land on which we can grow food, and this only compounds the problem. Every effort should me made in order to find substitutes for hazardous materials, or we may simply need to make a decision that we do not want to use or cannot use that material any more. Increasing population combined with less available farming land will only accelerate this problem, and may lead to widespread famine, disease and economic instability.

Agriculture

1) Graham, I, 2004, 'Soil: A Resource Our World Depends On', Heinemann Publishing, ISBN: 1403456267
2) Huxta, B, 2007, 'SOIL', Organic Gardening, vol.54, no.5, p.22
3) Montgomery, D. R, 2007, 'Soil Erosion and Agricultural Sustainability', Proceedings of the National Academy of Sciences of the United States of America, vol.104, no.33, pp.13268-13272
4) Soil erosion by Maurice Chedel, licence CC 3.0, Available: http://commons.wikimedia.org/wiki/File:Soil_erosion_near_Huancabamba.jpg
5) Rulli, M. C., Offeddu, L., & Santini, M, 2012, Modeling Postfire Water Erosion Mitigation Strategies', Hydrology and Earth System Sciences Discussions, vol.9, no.9, pp.10877-10916
6) Bertol, I., Mello, E. L., Guadagnin, J. C., Zaparolli, A. L. V., & Carrafa, M. R, 2003, 'Nutrient Losses by Water Erosion',Scientia Agricola, vol.60, no.3, pp.581-586
7) Edwards, C, 2005, 'Desertification', Geographical, vol.77, no.2, p.44
8) Desertifacio by Leo Nunes, licence CC 3.0, Available: http://commons.wikimedia.org/wiki/File:Desertificacao.jpg
9) Reeve, P, 2003, 'Protecting Land From Contamination', The Safety & Health Practitioner, vol.21, no.11, p.18
10) AlMaarofi, S., Douabul, A., & Al-Saad, H, 2012, 'Mesopotamian Marshlands: Salinization Problem', Journal of Environmental Protection, vol.3, no.10, pp.1295-1301
11) Harjula, H, 2006, 'Hazardous Waste',Annals of the New York Academy of Sciences, vol.1076, no.1, pp.462-47
12) Buckland, J, 2002, 'Hazardous Waste Disposal', Nature Reviews Immunology, vol.2, no.4, p.220

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