Главная Экология Введение в оценку экологических рисков
4 Soil Pollution: Classification and Effects
Lead-in Comment upon the statements. Express your opinion.
As soils are depleted, human health, vitality and intelligence go with them.
Bromfield Louis. Writer (1896-1956) When the soil disappears, the soul disappears.
Exercise 1. Read and remember the pronunciation
[i:] seep, leach, beneath, release
[o:] cause, course, enormous, fauna
[э:] herbicide, fertilizer, disturb, fertile
[Л] crux, ultimate, consumption, reduction
[u:] improve, remove, include
[ai] hydro, bio, biology, biodegrable, virus, fiber
[k] chloride, chronic, chemical, biochemical
 measure, erosion, regime
With rapidly advancing technology man’s impact upon the world of natural resources is beginning to prove overwhelming. Rapid urbanization with the consequent increase in population and building has resulted in the reduction of lands for the wastes to be disposed. Every year solid wastes are increasing tremendously all over the world depending on living standards of people. Moreover, several hazardous chemicals and mountains of wastes are ultimately dumped on the land. Dumping of industrial and municipal wastes causes toxic substances to be leached and seep into the soil and affects the ground water course (Fig. 4).
The crux of the waste problems in land lies in the leachates and great amount of wastes. Such leachates percolate out of garbage heap are known to move slowly through the layers of soil beneath and contaminate the water resources deep down the land. However, the problem of soil pollution differs from air and water pollution in the respect that the pollutants remain in direct contact with the soil for relatively longer periods. The wide-spread industrialization and increasing consumption have changed the very complexion of soil. Thus, soil is getting heavily polluted day by day by toxic materials and dangerous microorganisms released into air, water, and food chain. For all this man is the original and basic pollutant responsible for pollution hazards and toxic effects.
Fig. 4. Process of soil pollution
Soil pollution results mainly from the following sources: industrial wastes, urban wastes, radioactive pollutants, agricultural practices, chemical and metallic pollutants, biological agents, mining, resistant objects, soil sediments.
Disposal of industrial waste is the major problem responsible for soil pollution. Industrial pollutants are mainly discharged from pulp and paper mills, chemical plants, oil refineries, sugar factories, tanneries, textiles, etc. Many industrial effluents are either discharged into streams or dumped into surrounding area. Industrial wastes mainly consist of organic compounds along with inorganic complexes and non-biodegradable materials. These pollutants affect and alter chemical and biological properties of soil. As a result, hazardous chemicals can enter human food chain from soil or water; disturb the biochemical processes finally leading to serious effects on living organisms.
Urban wastes (Fig. 5) comprise both commercial and domestic wastes consisting of dried sludge of sewage. All urban solid wastes are commonly referred to as refuse. Solid waste or refuse contribute to soil pollution. They contain garbage (or rubbish) materials like plastics, glasses, metallic cans, fibers, paper; street sweepings, fuel residues, leaves, containers, abandoned vehicles and other discharged products. Soil gets enormous quantities of waste products each year. Much of sulphur dioxide evolved during burning of sulphur containing fuel ends up on soil as sulphates which react with soil water to form sulphuric acid.
Fig. 5. Urban wastes
Modem agricultural practices pollute soil to a large extent. Today with advancing agro-technology huge quantities of fertilizers, pesticides, herbicides and soil conditioning agents are employed to increase the crop yield. Many agricultural lands have now excessive amounts of plants and animal wastes which pose soil pollution problem. Apart from farm wastes manure slurry, debris, soil erosion containing mostly inorganic chemicals are reported to cause soil pollution.
Nowadays the most commonly anticipated problem is soil contamination with toxic chemicals. Well documented constituents include mercury, chloride, nitrite, zinc, iron and cadmium which have adverse effects on crop productivity. Toxic metals may be absorbed by plants grown in contaminated soil and then accumulate in animals eating the plants reaching the chronic toxic levels. However pollution control methods significantly reduce indiscriminate dumping into sewer lines. Sewerage sludge could become a product with lesser extents of potential hazards.
But soil gets also large amount of human, animal and birds excreta constituting the major source of land pollution by biological agents. Digested sewage sludge as well as heavy application of manures to soil without periodic leaching could cause chronic salt hazard to plants within a few years. Besides, faulty sanitation, municipal garbage, waste water and wrong methods of agricultural practices also induce heavy soil pollution. Sludge contains harmful viruses and viable intestinal worms. In developing countries intestinal parasites constitute the most serious soil pollution problems.
Another source of pollution is mining activity. In surface and strip mining the top and sub soil is removed. So, soil damage and environmental degradation during mining is inevitable as vegetation has to be removed too, and huge amount of top soil and waste rocks are to be shifted to a new location. That’s why mining leads to loss of grazing and fertile lands, soil erosion from waste dumps, sedimentation and siltation, danger to aquatic life, damage to flora and fauna as well as soil pollution.
To solve these problems the rehabilitation strategy needs to be broad based and made interdisciplinary. Appropriate cost effective measure includes storage of top soil, selection of ecologically and socio-economically suitable species, improvements in hydrological regime, support in afforestation, fuel wood conservation etc.
Exercise 2. Translate the words paying attention to the word formation
To degrade - degradation - degradable - biodegradable - non- biodegradable
Forest - forestation - afforestation - deforestation
To produce - product - production - productivity
Sewer - sewage - sewerage
To sanitate - sanitary - sanitation
Exercise 3. Match the synonyms from A to В
Exercise 4. Fill in the necessary preposition where necessary
Exercise 5. Complete the sentences translating the Russian words
Exercise 6. Answer the following questions
Exercise 6. Match the beginning of the sentences with their ending.
Exercise 7. Read an article about ways of reduction in soil erosion in the process of farming. Six paragraphs have been removed from the article. Choose from the paragraphs A-H the one which fits each gap (1-6). There is an extra paragraph which you do not need to use.
There is an example at the beginning (0).
Soil erosion and soil sustainability
Soil eroded from one location has to go somewhere else. A lot of it travels down streams and rivers and is deposited at their mouths. U.S. rivers carry about 3.6 billion metric tons per year of sediment, 75 % of it from agricultural lands. That’s more than 25 000 pounds of sediment for each person in the United States. 0_- (A) _ Of this total, 2.7 billion metric tons per year are deposited in reservoirs, rivers, and lakes. Eventually, these sediments fill in these bodies of water, destroying some fisheries. In tropical waters, sediments entering the ocean can destroy coral reefs near a shore. The sediment deposits on the reefs block out the sunlight that photosynthetic reef organisms need, and can also cause other damage to the reefs, especially if the sediments contain toxic chemicals.
Soil eroded from farms carries chemicals that affect the environment. Nitrates, ammonia, and other fertilizers carried by sediments increase the growth of algae in water downstream (a process called eutrophication) just as they boost the growth of crops, but people generally do not want algae in their water. 1_.
It’s not enough for crops to be sustainable - the ecosystem must be, too. At this point in our discussion we have arrived at a partial answer to the question: How could farming be sustained for thousands of years, while the soil has been degraded? However there is a difference between the sustainability of a product (in this case crops) and that of the ecosystem. 2_.
Soil forms continuously. In ideal farming the amount of soil lost would never be greater than the amount of new soil produced. Production of new soil is slow - on good lands the formation of a layer of soil 1 millimeter deep (thinner than a piece of paper) may take 10^10 years. 3_.
Plowing creates furrows and if they go downhill, then the water pours down these paths carrying a lot of soil with it. In contour plowing the land is plowed not up and down but as horizontally as possible across the slopes. Contour plowing has been the only most effective way to reduce soil erosion. 4_.
An even more efficient way to slow erosion is to avoid plowing altogether. No-till agriculture (also called conservation tillage) involves not plowing the land, using herbicides and integrated pest management to keep down weeds, and allowing some weeds to grow. Stems and roots that are not part of the commercial crop are left in the fields and allowed to decay in place. In contrast to standard modem approaches, the goal in no-till agriculture is to suppress and control weeds but not to
estimate them if doing so would harm the soil. 5_.
A. Of this total, 2.7 billion metric tons per year are deposited in reservoirs, rivers, and lakes. Eventually, these sediments fill in these bodies of water, destroying some fisheries. In tropical waters, sediments entering the ocean can destroy coral reefs near a shore. The sediment deposits on the reefs block out the sunlight that photosynthetic reef organisms need, and can also cause other damage to the reefs, especially if the sediments contain toxic chemicals.
B. In agriculture, crop production can be sustained while the ecosystem may not be. And if the ecosystem is not sustained, then people must provide additional input of energy and chemical elements to replace what is lost.
C. The water develops a thick, greenish-brown mat, unpleasant for recreation and for drinking. In addition, because the dead algae are decomposed by bacteria that remove oxygen from water, fish can no longer live in that water. Sediments also can carry toxic chemical pesticides. Efforts to limit soil erosion have reduced the amount of agricultural sedimentation since the 1930’s. Even so, taking into account the costs of dredging and the decline in the useful life of reservoir, sediment damage costs the United States about $ 500 million a year.
D. Sustainability of soils can be aided by fall plowing and no-till agriculture - that is, planting without plowing. More than 250 acres of farmland are treated one way or another to improve soil conservation.
E. Worldwide no-till agriculture is increasing. Of course, like so many things are done, no-till involves trade-offs - for example, it requires greater use of pesticides. But decreased erosion means that a small percentage of these pesticides will be transported off the agricultural fields, and the pesticides will have a longer time to decompose in place.
F. The physical aspects of sustainability are partly understood. Practices that can cause long-term damage to soil include excessive tillage and irrigation without adequate drainage. Long-term experiments have provided some of the best data on how various practices affect soil properties essential to sustainability. The most important factors for an individual site are sun, air, soil and water. Of the four, water and soil quality and quantity are most amenable to human intervention through time and labour.
G. This was demonstrated by an experiment on sloping land planted in potatoes. Part of the land was plowed in rows running downhill, and part was contour-plowed. The up-and-down section lost 32 metric tons of soil per hectare (14.4 tons per acre). The contour-plowed section lost only 0.22 metric ton per hectare (0.1 ton per acre) as shown in Figure. It would take almost 150 years for the contour-plowed land to erode as much as the traditionally plowed land eroded in a single year!
Fig. 6. Plowing
Fig. 7. Comparison of conventional and по-till agriculture
Fig. 8. No-till agriculture