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Human activities can impose far-reaching effects on the environment

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Over the last two hundred years, the human population has grown exponentially. In the process of trying to satisfy the needs of these growing numbers, we have changed our planet; for example, millions of hectares of forests have been cleared to supply timber and land for homes and agriculture, deserts have grown, some rivers have dried up, and the air and oceans have been polluted. The Second World War reminded many countries of the importance maintaining self-sufficiency in basic foods, In the UK, between 1945 and the mid-1980s; the overriding aim of agricultural policy was to increase production. Food production is the oldest industry of all. Without a source of food and energy, there can be no life, and it is perhaps not surprising that humans have drastically altered the natural environment in order to grow more food. The nature of agriculture in the UK changed more during these 50 years than it had done in the previous two centuries. Such changes had profound environmental effects (Figure 1.1 and 1.2) The result of all these changes has been that agriculture has become more intensive, producing higher yields per acre by relying on greater chemicals use and technological inputs. It also has become more expensive, relying on purchase of machinery and chemicals to replace the heavy labour requirements of the past. To remain competitive, farmers have been forced to become more efficient, farming ever-larger acreages with bigger equipment and more fertilizers and pesticides. Much larger farms consisting of extensive fields of a single crop have in large part replaced small farms growing a wide variety of crops. Farmers manipulate the natural environment so that they get as much food as possible from their land. In doing so, they create new ecosystems - agroecosystems, which are very different from natural unmanaged ecosystems. Agroecosystems are simpler than wilder ecosystems - they have less plant and animal genetic diversity and a less complex spatial structure. ...read more.


Many modern agricultural practices have led to increased soil erosion (the loss of vital topsoil by agents of erosion such as wind and water). Organic matter is vital to soil structure. Unlike organic fertilisers, inorganic fertilisers, which are now more commonly used, add no organic matter to the soil. Reliance on such fertilisers may mean that the soil is not bound together by humus and this can lead to soil erosion. Any vegetation that covers the soil will tend to reduce soil erosion, so agricultural soils are most vulnerable when the crop has been harvested and the soil is left bare. Finally, the use of heavy machinery will lead to soil compaction and loss of structure, which may speed up soil loss. Erosion affects productivity because it removes the surface soils, containing most of the organic matter, plant nutrients, and fine soil particles, which help to retain water and nutrients in the root zone where they are available to plants. The sub-soils that remain tend to be less fertile, less absorbent, and less able to retain pesticides, fertilizers, and other plant nutrients. The effects of erosion are also felt elsewhere in the environment. Eroded soil clogs streams, rivers, lakes, and reservoirs, resulting in increased flooding, decreased reservoir capacity, and destruction of habitats for many species of fish and other aquatic life. The eroded soils contain nutrients and other chemicals that are beneficial on farm fields, but can impair water quality when carried away by erosion. As a result, drinking water supplies may contain nitrate or organic chemicals in concentrations that exceed public health standards, or surface waters may become clogged with excessive plant growth from the added nutrients. Traditionally, farmers that grew the same crop repeatedly in the same place eventually removed various nutrients from the soil. One way that farmers avoided a decrease in soil fertility was to practice crop rotation, by which different crops were planted in a regular sequence so that a crop that leaches the soil of one kind of nutrient is followed during the next growing season by a crop that returns that nutrient to the soil. ...read more.


Methane from livestock Principal greenhouse gas. Nitrogen I oxide from breakdown of nitrogen fertilisers Principal greenhouse gas and contributor to stratospheric ozone depletion. Figure 1.3: Problems with insecticides * Direct killing: accidental misuse of toxic chemicals may cause death in humans or in domestic animals. * Non-specificity: non-target species, particularly natural predators of the pest species, may be killed by some wide-spectrum insecticides, e.g. large doses of dieldrin killed many birds as well as the Japanese beetle pest which was the intended target organism. * Pest resistance: genetic variation means that each pest population contains a few resistant individuals. The pesticide eliminates the non-resistant forms and thus a resistant population is selected for and may quickly develop (since many pests reproduce rapidly). * Pest replacement: most crops are susceptible to attack by more than one species - a pest complex and the use of a pesticide to eliminate one species may simply allow another species to assume major pest proportions (since a pesticide may be more deadly to one species than another). * Pest resurgence: non-specific pesticides may kill natural predators as well as pests - a small residual pest population may now multiply without check, creating a worse problem than initially was present. * Bioaccumulation of toxins: pesticides or their products may be toxic a) they may seriously affect micro-organisms and thus alter decomposition in soils; b) they may pass along food chains, becoming more concentrated in organisms further up the chain. Figure 1.4: Presently, large phytoplankton blooms during spring and summer are a characteristic feature of the Baltic, where approximately 30 different species of phytoplankton could be harmful. Blue-green algae form extensive, often toxic, blooms nearly every summer in the Baltic proper and the Gulf of Finland. Satellite imagery demonstrates that areas up to 60,000 km2 (~ 1/6 of Baltic Sea) are covered with blue-green algal blooms during the summer, most prominently in the Baltic Proper and the Gulf of Finland: Figure 1.5: Agriculture is the leading source of water pollution in rivers and lakes Christopher Magee Monday 6th October 2003 1 ...read more.

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