For example the pesticide DDT accumulates in the fatty tissues of carnivorous animals, inhibiting cytochrome oxidase and limiting reproductive success (especially thin eggshells in birds of prey). Thus, the overuse of persistent pesticides may lead to accumulation of these compounds in food chains. The top carnivores consume many organisms from lower down the food chain, and so ingest high levels of pesticide. Other organic molecules from the prey are respired, so the relative concentration of the pesticide increases. Hence DDT's ability to spread through the food chain was especially insidious because the chemical was able to bioaccumulate and bio-magnify.
Bio-magnification is a process by which some organisms accumulate chemical residues in higher concentrations that those found in the organism they consume. After application as a pesticide, DDT was found in waterways in low concentrations; but DDT had biomagnified 10 million times by the time it had reached the top of the food chain; the birds.
Because of the problems from using organochlorine pesticides, new pesticides have been developed. These chemicals are not as persistent in the food chain as organochlorines, but some are more immediately toxic to wildlife. Others are extremely toxic to certain non-target species like bees, fish and aquatic invertebrates.
The toxicity of pesticides to wildlife depends on several factors, including the persistence and degree of toxicity of the chemicals. Factors such as dose, time and duration of application play important roles in a pesticide’s toxicity. Wildlife, for example, is more susceptible to pesticides effects during nesting, nursing of young or during times of low food availability.
A pesticide’s degree of toxicity also depends on how it is exposed to wildlife. Primary exposure includes eating, drinking, preening feathers, skin contact or breathing of vapors. Secondary exposure occurs from scavenging on contaminated food, such as exposed carcasses, or feeding upon insects. If pesticide levels are high enough, wildlife often dies suddenly.
Not as readily observed in wildlife are the sub-lethal, or non-fatal, consequences of ingesting pesticides. Behavior changes, weight loss, impaired or unsuccessful reproduction, high offspring mortality or deformed embryos are results of sub-lethal exposure to pesticides. Affected wildlife becomes easy prey for predators, while many loose their ability to adapt to environmental changes.
Pesticides can reduce insects that may be important food sources for young birds and fish, and habitat is similarly reduced when vegetation is destroyed – a critical factor for small wildlife populations already stressed by insufficient habitat. Research continues to find other sub-lethal effects linked to pesticides, which could affect threatened and endangered species as well as humans. As pesticides inadvertently destroy beneficial organisms, pest species often flourish.
The use of machinery to replace manual and animal had begun before the Second World War but rapidly accelerated thereafter. Widespread use of machines offered immediate advantages, and productivity was increased by the use of larger and more effective implements, such as deep-cutting ploughs. Land, which had previously been used to provide fodder for draft animals, could now be sown with crops for direct human consumption.
Jobs such as harvesting could now be done in a fraction of the time that manual labour would take. By making such operations less dependant on the weather, wastage of crops was reduced, further increasing productivity. Mechanisation also led to the increasing use of monoculture – large areas of land devoted to one single crop, species, strain or even genotype. Monocultures increased the risk of pest epidemics, leading to an increase in the use of pesticide or of deficiencies of particular soil nutrients, further intensifying the use of fertilisers. Furthermore, large machines are only efficient when making long straight runs – combine harvesters and huge ploughs cannot work around corners – so huge fields were created by destroying field boundaries, such as hedgerows, walls and ditches. The removal of hedgerows could be an agricultural advantage as more land would be available enabling an easier use of large machinery. There would also be less inter-specific competition for water, light and nutrients close to the hedge. Moreover there would be fewer pests living in the hedge.
However as hedgerows decrease wind speeds, their removal could result in many disadvantages – for instance it may accelerate soil erosion, as there would be no wind barriers to shield exposed fields from strong wind. In addition entire ecosystems (biodiversity) would collapse, including a loss of predators living in the hedge to neutralise pest problems.
Fertile soil is an important physical input into agriculture. 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.
Legumes in the rotation were used to increase the available soil nitrogen. Symbiotic nitrogen-fixing bacteria called rhizobia form nodules on the roots of legume plants and convert or fix atmospheric nitrogen to organic nitrogen. The amount of nitrogen fixed varies with species, available soil nitrogen, and many other factors. Fixed nitrogen not removed from the land by harvest becomes available to succeeding crops as the legume tissues undergo microbial decomposition. When the legume crop was seeded, rhizobia inoculum was applied to the seed to ensure the most productive commercial strains were available to form nodules and that inoculating bacteria were always present.
Hence if crop rotation is done properly, farmers could keep their fields under continuous production, without a need to let them lie fallow or to apply artificial fertilizers. The three major nutrients in fertilizers are nitrogen, phosphorus, and potassium. Of these, nitrogen is the most readily lost because of its high solubility in the nitrate form. Leaching of nitrate from agricultural fields can elevate concentrations in underlying groundwater to levels unacceptable for drinking water quality.
Potassium does not cause water quality problems because it is not hazardous in drinking water and is not a limiting nutrient for growth of aquatic plants. It is tightly held by soil particles and so can be removed from fields by erosion, but generally not by leaching.
Phosphorus, the third major nutrient in fertilizers does not leach as readily as nitrate because it is more tightly bound to soil particles. However, it is carried with eroded soils into surface water bodies, where it may cause eutrophication.
Eutrophication is a condition in an aquatic ecosystem where high nutrient concentrations stimulate blooms of algae e.g., phytoplankton (see Figure 1.4). Although eutrophication is a natural process in the aging of lakes and some estuaries, human activities can greatly accelerate eutrophication by increasing the rate at which nutrients and organic substances enter aquatic ecosystems from their surrounding watersheds. Thus, cultural or anthropogenic "eutrophication" is water pollution caused by excessive plant nutrients. Agricultural runoff, urban runoff, leaking septic systems, sewage discharges, eroded stream banks, and similar sources can increase the flow of nutrients and organic substances into aquatic systems. These substances can over stimulate the growth of algae, creating conditions that interfere with the recreational use of lakes and estuaries, and the health and diversity of indigenous fish, plant, and animal populations.
Algal blooms hurt the system in two ways. First, they cloud the water and block sunlight, causing larger submerged aquatic vegetation (SAV) to dieback. Because these grasses provide food and shelter for aquatic creatures (such as the blue crab and summer flounder), spawning and nursery habitat is destroyed and waterfowl have less to eat when grasses die off. Second, when the algae die and decompose, oxygen is used up. Dissolved oxygen in the water is essential to most organisms living in the water, such as fish and crabs. Increased eutrophication from nutrient enrichment due to human activities is one of the leading problems facing some estuaries in the mid-Atlantic.
Phosphorus, attached to sediments derived from soil erosion, may accumulate in the sediments of lakes and streams. This phosphorus may be recycled slowly or released more rapidly when these sediments are disturbed, for example during a storm or flood. Pollution due to the excessive use of phosphorus (see Figure 1.5) is therefore a long-term problem.
This situation indicates the urgent need for exploring alternative technologies, that although do not achieve fabulous increases in the levels of the production, tend instead to achieve stable yields in the time (sustainability). That is that there should be undertaken the road toward an agriculture that as premise has the sustainability, recovering the ecological dimension of the production, promoting the use, insofar as possible, of inputs and locally available resources, as dung of family livestock, associated cultures, crop rotation and other agro-ecological practices, aspect that by logical consequence, will produce products and wholesome food for benefit of the consumer and without causing health impairments of the producer, of the consumer, nor of the environment, in addition to the contribution of the conservation of the biodiversity
At present modern techniques of farming are focused around genetically modified crops, which are designed to grow at an increased rate and are resistant to certain diseases. Although these are considerable advantages to farming, genetically modified crops are believed to cause unpredictable and pose unexpected problems as well as great risks to the country's biodiversity; however the truth is that the disadvantages are not yet fully understood.
As European countries have huge surpluses of staple foods, they begun to look at ways of decreasing production and making agriculture more environmentally friendly. Meanwhile, many developing countries are still far from sufficient in basic foodstuffs, and thus look set to implement the same environmentally damaging and perhaps unsustainable techniques that the West has used.
In conclusion the dramatic positive effects of rotations, multiple cropping, and biological control on crop health, environmental quality and agricultural productivity have been confirmed repeatedly by scientific research. Biotechnology should be considered as one more tool that can be used, provided the ecological risks are investigated and deemed acceptable, in conjunction with a host of other approaches to move agriculture towards sustainability.
Although modern farming techniques produce higher yields and can enable faster food ‘turn outs’ they are in turn destroying the natural balance of ecosystems. However if countries where to use a traditional agricultural system of high biodiversity and low input, where the use of family labour, the use of locally renewable energies, with strong interaction with livestock production would reflect ecological and economic sustainability. It produces positive energy and economic returns to the system, what it confers is a profound agro-ecological commitment, guaranteeing the production of healthy food and products with different destinations called self-sufficiency and sale, in addition to becoming a microcenter of conservation of biodiversity. As nature is a key element to the existence of the human race, new techniques must be developed to limit damage to ecosystems.
Figure 1.1: Environmental problems caused by agricultural intensification
Figure 1.2: Agricultural Pollution Problems
Figure 1.3: Problems with insecticides
- Direct killing: accidental misuse of toxic chemicals may cause death in humans or in domestic animals.
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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).
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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