Some modern farming practices are damaging the environment and the destruction of habitats reduces the diversity of ecosystems, making them less stable and farming less sustainable. A balance is needed between increasing food production and the need for conserving the environment. Alternative strategies need to be used in order to achieve this. If organic fertilizers are used too much little humus is added to the soil, they damage communities of microorganisms involved in decomposition and the nitrogen cycle, it damages soil structure leading to increased erosion and it increases the risk of eutrophication due to run off. Organic fertilizers such as manure avoid these problems and release nutrients gradually as they are decomposed. Erosion results from monocultures, which leave fields without plant cover after ploughing and allows run off from rain to carry away soil, large fields with few hedges increase the wind blow of soil and the use of inorganic fertilizers which destroys soil structure making it easier to erode. This can be avoided by using crop rotation and winter plantings to keep soil covered, planting hedges as wind breaks and use of organic fertilizers to improve soil structure. Pesticides should be biodegradable, pest-specific as possible to avoid killing other species, used at appropriate times when a pest outbreak is forecast, used when climatic factors are appropriate, e.g. low wind to avoid spray drift, applied appropriately e.g. spot spraying, rather than aerial spraying and alternatives should be considered e.g. biological control. Habitat variety can be maintained by, planting hedges and trees in the corners of fields and leaving ‘headlands’ strips around the edges of fields unsprayed with fertilizer or pesticides where wild species of plants and animals grow with the crop.
A number of domestic, agricultural and industrial processes contribute to water pollution. These processes occur firstly due to heavy metal ions from industrial outflows entering the water system accidentally. An example of this was in Minimata, Japan where a mercury compound was discharged into seawater. Shellfish absorbed this and they did not die from it. However humans consumed the shellfish, where the toxin had built up (bio-accumulation). The humans consequently suffered severe problems with their nervous system. Oil spillages are another source of water pollution. These occur as a result of tankers accidentally spilling crude oil into the sea. This is catastrophic as oil floats and Oxygen diffusion from in the air is inhibited by the resultant oil slick. The aquatic organisms often die due to lack of oxygen and plants can’t achieve light for photosynthesis. Below the oil putrefaction can take place and bacterial action leads to the highly toxic gas, hydrogen sulphide been produced. Additionally oil affects the feathers of water birds and contamination can result in their inability to fly and they lose their buoyancy. Another cause of water pollution is suspended solids, which can cause many problems for organisms. The suspended particles intercept light, reducing photosynthetic productivity, which has an adverse effect on the consumers in food chains. The pottery industry has contributed to this problem in the past, because fine particles such as waste china clay are particularly harmful. The particles are so small bivalves such as mussels take them in. These filter feeders cannot cope with the sheer volume of particles and perish as their feeding and gaseous exchange mechanisms are inhibited. If particles continue to silt up the bottom of the water habitat then many more organisms are harmed by the continued coverage, e.g. bloodworms (Tubifex). Excess mineral ions such as phosphates and nitrates in sewage are another cause of water pollution. This is because even though low amounts of nitrates and phosphates would be beneficial to aquatic plants, in excess amounts they are harmful and cause algal blooms, which result in eutrophication, which is when the minerals ions/nutrients in water increase above normal levels removing limiting factors on the exponential growth of the algae. The algae cover other species of water plants in the community, preventing them from getting light and killing them. This reduces oxygen in the water and producers in the food chain. Exponential growth of algae produces more dead algae providing food for growth of decomposing bacteria and higher Biochemical Oxygen Demand. Decomposition of organic effluent releases nitrate and phosphate ions. Excessive use of nitrate/phosphate based fertilizers leads to the ions been washed into streams, rivers, lakes after rain. Pesticides are another contributory factor in water pollution. These include insecticides, fungicides and molluscicides. The main role of these is to kill only the target pests but they can also affect other organisms. Run off and leaching transports them to the rivers. Persistent pesticides such as DDT remain in the ecosystem for long periods. Insects affected by the DDT enter the food chain and the DDT accumulates in the fatty tissues of these insects. The DDT passes through rivers and seas all over the world, even where it isn’t used. It was banned in the UK many years ago but it still remains in the soil and can still be detected in some animal tissues. Organophosphates have been used to replace the organochlorines, being less persistent. However they are toxic to humans as well as insects. In humans they inhibit the action of acetylchlorine esterase at synapses. Also if these chemicals reach water habitats they may be accumulated along food chains quickly. Thermal pollution occurs as coolant water is returned to rivers from power stations.
A number of strategies have been introduced in order to control water pollution. These are, using biological control to target specific pests rather than using pesticides. Composition of organic waste reduces the use of organic fertilizers. This means that there will be a slow release of ions and better holding capacity, which ensures that less ions reach the rivers by run-off and leaching. A new technique has also been introduced to see whether insecticides are in the environment. This is Lethal Dose50, which is given orally and kills about 50% of the population in the laboratory. Some people have ethical objections to LD50 testing and alternative tests using laboratory-cultured tissues are also used.
Gases reach the atmosphere in the number of ways including combustion of fossil fuels, industrial emissions and microbial processes. Gases reaching the air include sulphur dioxide, carbon dioxide, carbon monoxide, nitrogen oxides, chlorofluorocarbons (CFC’s), and methane and smoke particles. Large amounts of these gases can have very serious effects. The greenhouse effect is caused by a number of gases, but water vapour and carbon dioxide have the most effect due to their high volume in the troposphere. CFC’s have a stronger potential contribution to the greenhouse effect but are found in smaller quantities. Industries have traditionally been very defensive about admitting to the production of harmful waste gases. Polychlorinated biphenyls (PCB’s) are good examples of known dangerous emissions. These are used in plastics manufacture, and they are released during this manufacture. However more is given off during incineration of plastics waste. They can build up in animal tissues and have been found in fat cells in seals. PCBs are also considered to be carcinogenic. Air pollution is a threat to the Ozone layer because chlorine, nitrogen oxides and CFCs react to break down it down by a variety of mechanisms. This Ozone layer (O3) is high up in the stratosphere at about 20-30km and is important because it absorbs UV radiation. This therefore prevents humans from getting skin cancer, cataracts and problems with their immune systems.
Air pollution will be decreased if there is a legislation and international agreement to limit or ban toxic emissions, such as, sulphur dioxide reduction. Cars could use low sulphur fuel and catalytic converters to prevent too many toxic emissions. Methane gas is produced from organic waste and is an excellent alternative to fossil fuels. Also scrubbing of waste gases at coal-fired power stations reduces SO2 emission.
In conclusion it is clear that humans are having a major impact on the environment in terms of water, air and farming pollution. This is mainly due to the fact that alternative strategies (i.e. pollution controls and recycling) are not been put into practice as effectively as they could be. There needs to be government legislation and national agreements if these strategies are to be effective in reducing the effects of pollution over time.
