HUMAN IMPACT ON THE NATURAL ENVIRONMENT

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Man’s relation with his natural environment is a complex one. While he is subject to certain natural controls and events, he also acts as the dominant force in many of the Earth’s physical and biological systems. The relationship has changed with time. For thousands of years, the direction and extent of his progress were to a considerable measure dictated by his physical environment, which sometimes presented him with very difficult obstacles. Increasingly, man has become capable of altering his physical environment to suit himself. Although the object of these alterations was to improve his living conditions, in some cases they have created major long-term problems, and in still others they have been catastrophic, both for the natural environment and himself.

In some parts of the world, the environment has been so transformed that few elements of its original nature are detectable. Even extreme habitats such as the tundra or hot deserts only sparsely populated by man have not escaped untouched, since they are often the most sensitive to the slightest interference. Many apparently natural systems are in fact control systems in which man acts as a regulator either consciously or inadvertently. At best, except for large-scale weather phenomena, natural systems are mostly modified systems.

Modification of Landforms. Mining and quarrying, deforestation, the introduction of exotic plants and animals, the use of agricultural machinery, the building and use of tracks and roads, and the overgrazing of pastures, have all, singly and in combination, profoundly altered landforms and caused accelerated erosion and deposition to occur. Where man excavates or piles up material himself, he can be regarded as a direct agent of change; where he causes natural landform processes, such as wind and water action, to accelerate or diminish, he is acting in an indirect manner. Indirect effects are by far the most widespread. Much of this influence occurs accidentally or secondarily to some other purpose; conscious attempts to influence landform processes – for example, by building coastal groynes or by reafforestation – are inevitably expensive and limited in extent.

Direct Alteration of Landforms. Man has a direct effect on the shape of landforms by excavating and pilling up earth, reclaiming land from the sea and causing subsidence through mining. These activities have greatly increased since the Industrial Revolution with the development of enormous machine power and explosives for moving material. Railway and motorway construction provides many familiar examples of man-created slopes, embankments and cuttings. Land scarification is sometimes used as a general term for disturbances created by the extraction of mineral resources; open-pit mines, quarries, sand and gravel pits are among the forms of scarification. Strip-mining is one of the most devastating examples of landform alteration of this kind. Although common in the United States, it does not occur on a widespread scale in Britain, except as a method of mining Jurassic ironstone in Northamptonshire. The effects of subsidence are common in most of the older coal-mining areas of Britain. Switchback roads, perched canals, fractured buildings and flooded depressions or flashes are all visible manifestations of recent changes in the surface form of the ground.

Equally obvious as man-created landforms are coal tips and other waste heaps from mining and quarrying. Many of these features are geomorphologically unstable, allowing various forms of mass movement to generate. When saturated by heavy rain, spoil tips are frequently subject to sliding and flowage, supplying sediment that clogs stream channels. In 1966 at Aberfan in Wales, a major disaster occurred on a spring-saturated coal waste heap which moved as many of its children. Similar problems may arise on other constructed slopes: the large number of earth flows triggered during the building of the Panama Canal is a well-known example. More recently, the building of new trunk roads and motorways in Britain has encountered slope failure in several instances: at Port Talbot, Keele and Sevenoaks, excavation reactivated slope shear planes which were last active under periglacial conditions during the Devensian glaciation. These sites required extensive engineering works to stabilise or avoid the slopes.

Indirect Effects: Slopes and Rivers. By far the most important of all man’s effects on landforms are those connected with his interference with the natural vegetation, in particular with the clearing of forest for agricultural purposes. There is a close relationship between the amount of vegetation cover and erosion rates on hillslopes, and hence with the amount of sediment in streams. A stable vegetation cover acts as an effective regulator of natural erosion, protecting the ground from direct raindrop impact, absorbing some of the run-off, and making the slope more cohesive. With the removal of the vegetation, the surface loses its plant litter, causing a loss of soil structure, cohesion and porosity. Overgrazing has similar effects, and the introduction of animal pests such as the rabbit into Australia has also had a detrimental effect on slope stability.

Multiple shoe-string rills and gullies on hillsides are often a typical manifestation of man’s indirect effect on slopes. They are presently found in many parts of the world, notably in semi-arid regions susceptible to tropical downpours. In an area such as South Australia, the recent date of a great deal of gully and sheet erosion on slopes is testified by the burial of fence-posts and other man-made debris. There is evidence that in some long-settled areas of the world, like western Europe, where gullies are not now a prevalent feature of the landscape, they were more widespread in past times when the natural vegetation cover was first removed. We may note that it is not always easy to distinguish between the effects of man and a changing climate on hillslope erosion. For example, in the Mediterranean area during the latter part of the Roman period, there was an increasing loss of soil fertility, hillslopes became eroded and valley bottoms were heavily silted. This may have been the result of a tendency towards greater aridity, but many experts believe that human overpopulation and overgrazing by goats were important contributory factors.

(Bryant, Richard H. Physical Geography Made Simple)

● Name man-created direct and indirect alteration of landforms. Complete the table.

direct alteration of landforms	indirect alteration of landforms

3. Read the passages and number them in the correct order. Choose the best title to the text.

Soil Conservation / Ecosystem Management / Man’s Impact on the Environment / The Conservation Movement

A) A second element of ecosystem management, one which has come much more to the fore in recent years, is that of maintaining sustained yield from organic resources. This idea was first applied to the maintenance of the breeding stocks of marine animals and to forestry practice. It is also implicit in the principles of soil conservation, the aim of which is to sustain agricultural fertility. Many authorities would maintain that this is by far the most important aspect of ecosystem maintenance, and that in the face of growing pressure on food resources, the protection of wild life for non-productive reasons is a luxury we can ill afford.

B) In summary, there clearly is a need to ensure that environmental management permits the maximum use of biological resources consistent with the maintenance of the greatest diversity of organic life.

C) As applied to organic resources, one aspect of environmental management is the preservation and protection of wild life or of natural habitats from modification and depletion by man. This may be carried out for a combination of ethical, scientific or aesthetic reasons. To this end, nature reserves, wildlife refuges and similar controlled areas have been set up all over the world, designed to protect a particular habitat and its communities. These have not always been entirely successful. A classic example of the lack of understanding of ecological principles occurred with the establishment of National Parks in East Africa: these were designed originally to protect game animals, man being excluded except as a sightseer. But as a result, animals such as elephant, hippo and buffalo, whose populations had formerly been kept in check by hunting, increased to an extent that widespread devastation of their habitat resulted. What has been often overlooked in the past in environmental management is, first, that ecosystems cannot simply be “preserved”, but are dynamic in character, and second, man is an important habitat factor in many cases: the ecological niche occupied by him cannot suddenly be left vacant.

D) The widespread current concern over the status of ecosystems is the product of a movement that has slowly been gathering momentum over the last hundred years or so. Early efforts at the conscious management of biological resources often arose out of economic necessity: the imminent disappearance of the last forests in Britain and central Europe in the eighteenth century prompted landowners to adopt methods designed to save the last remaining forests and to stimulate forest productivity. The conservation movement as such was born in the United States. The ruthless clear-felling of great stands of forest in the western states and the experience of the Kansas dustbowl in the 1930s served to focus attention on the problem. Currently, of course, conservation has become a much wider issue than the maintenance of natural biological systems.

E) Modern environmental management policies attempt to reconcile these apparently conflicting aims – namely, preservation and productivity. Multipurpose schemes are often now attempted. This is most successfully applied to management of forests, which because of their size are often well suited to a variety of uses – for timber, wildlife conservation, water supply and recreation. In Britain, National Reserves are now managed as multiple resource units.

Model: 1 – D

4. Read the text Environmental Protection and correspond the facts with the following numbers: 1815 / 1816 / 1915 / 16, 000, 000 / 500, 000.

ENVIRONMENTAL PROTECTION

Everything has to be learned from nature and history …

In 1815, the Tambora volcano in Indonesia exploded, emitting such a large quantity of dust, smoke and soot into the atmosphere that the average annual temperature of the planet dropped by 1˚ C. This was enough for Europe and America to miss a summer and for the crop there not to ripen in 1816. A hundred years later, in 1915, there was a forest fire in Siberia. The fire, which destroyed 16 million hectares of forest, went on for several weeks, with smoke screening the Earth from the Sun. Grain crops failed and grass didn’t grow over a huge expanse.

Nature has modelled a “nuclear winter”, having made a tiny copy from it for our edification.

The discovery of “nuclear winter” should, by the logic of common sense, make war a thing of the past.

Nature has been suffocating from industrial pollution for a long time. The figures of the Earth’s ecological calamities are distressing. Forests are disappearing at the rate of 20 hectares per minute, or more than 500, 000 hectares a year. The volume of atmospheric oxygen annually decreases by 10 billions tons – a consequence of the destruction of forests and the contamination of water reservoirs.

The planet’s genetic fund has sustained irretrievable losses: hundreds of species of animals, birds, fishes and plants have disappeared forever. All these figures, one being sadder than the other, show our race to ecological catastrophe. And although this doesn’t make things any easier, the understanding of the scale of calamities is one of the factors shaping a new mode of thinking suitable for our time.

5. Read the text Environmental Factors through and make the review of it.

ENVIRONMENTAL FACTORS

Factors which have some effect on the life of an organism at some stage in its development are called environmental factors. These can be divided into groups as follows: first, a climatic group, which includes conditions of light, temperature, water availability and wind; second, topographic influences of slope angle, orientation and altitude; third, edaphic (soil) factors, especially pH and fertility; and fourth, biotic controls, such as a competition between species and the effects of grazing.

These groups are themselves interrelated so that it is extremely difficult to isolate the influence of individual factors. For example, topography and climate will influence soil development; and climate and soil will influence the pattern of biotic controls by determining the species which may inhabit a particular place and compete there for survival.

Light is extremely important environmental factor because it is the vital source of energy for ecosystems and it can also act as a control of functions such as reproduction and migration. Excess light can be a limiting factor in ecosystem development by damaging plant tissues and decreasing productivity.

The influence of light varies with its three main aspects: its quality (that is, wavelength composition), its intensity and its duration (day length).

Temperature is a universally important environmental factor both for its direct effects on organisms and for its indirect effects in modifying other factors such as relative humidity and water availability. Each species has its own minimum, maximum and optimum temperatures for life but the actual limits at any time vary with such things as the age of the individual and water balances in the body. Generally, aquatic plants and animals have narrower tolerance ranges for temperature than those which live on land. This is mainly because there is far more temperature variation in terrestrial ecosystems.

Water availability may often restrict ecosystem development because most organisms need large amounts of water to survive. It not only forms a large percentage of the tissues in plant and animal bodies but it is also essential for transport and cooling. In plants, water provides support and is essential for photosynthesis.

Distributions of plants may largely depend on the effectiveness of precipitation; this will be a function of the kind of precipitation, the type of vegetation present and the rate of evaporation. In many areas fog or dew is important in providing essential moisture for plant growth and thus extending the distribution ranges of species.

In the case of animals, water usually only acts as a limiting factor when it is in short supply. There is a great variation in the amounts of water needed different species but usually cold-blooded animals require less than warm-blooded ones, which use it for heat regulation. Some animals display specific adaptations for survival in arid habitats. Desert animals may avoid the hottest and driest season by becoming inactive – that is, aestivating.

Wind can act as an environmental factor either directly by causing mechanical damage to plants or indirectly by affecting relative humidity and evaporation rates. High wind velocities can cause an appreciable increase in the rate of transpiration and limit plant growth. In very exposed situations such as mountain summits, coasts and open plains vegetation may be dwarfed as a result of wind action.

Topography can influence ecosystem development in three major ways. First, by the direct effects of altitude on temperature. Temperature decreases as altitude increases either at the dry adiabatic lapse rate (10°C/km) or, more usually, at a lower rate than this, approximately 6°C/km. Second, topography can act indirectly, since temperature changes affect relative humidity. The combination of changes in temperature and relative humidity leads to the development of an altitudinal zonation of ecosystems. At a low level, desert merges into pine forests, which are succeeded by fir and spruce, and then by alpine communities at the highest altitude.

The third way in which topography can influence ecosystem development is by local variation in slope orientation and angle. South-facing sides of valleys receive strong incident light (in the northern hemisphere) and are therefore warmer and drier than north-facing slopes which are in the shadow for a lot of the time. This leads to great contrasts in species structure and productivity between sides of valleys. Angle of slope will be a critical factor in soil formation and drainage.

The soil is a vital component of terrestrial ecosystems, particularly in cycling nutrients without which all life would cease. Soil and the rest of the ecosystem are closely related; one will influence the workings of the other. Particular attributes of soils, such as texture, pH, soil climate and organic content operate in a closely interrelated fashion to exert control on rates of decomposition, nutrient cycling and plant distribution and productivity.

Soil texture is very important in determining the soil climate, since it affects aeration, drainage and ease of root penetration.

Biotic factors are the interactions that occur between living things. Biotic factors are usually far more diverse and intricate than other environmental controls because they rely on the activities of a wide variety of organisms.

Most habitats can be occupied by many different types of plants and animals. The success of a particular species will depend on its ability to obtain its requirements for life. Competition arises if the resources of a habitat are insufficient to meet the demands of all the organisms living there. Generally competition is most intense between individuals of the same species or of different species that have similar ecological niches, especially at young stages in the life cycle.

Man is by far the most important biotic factor. He has caused fundamental modifications of ecosystems by fire, hunting and agriculture, man has obliterated large areas of natural systems and caused pollution of both terrestrial and aquatic habitats.

6. Read the text Modification of the Atmosphere through and make the review.

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