Balance of Food Production and Conservation
Conservation aims to maintain biological diversity for the benefit of mankind. It involves formulating policies and regulations to protect and maintain populations of wild plants and animals, identifying and preserving habitats in which wildlife can flourish, controlling pollution of the environment and setting up agencies to promote and monitor conservation strategies.
However, due to many human activities biodiversity is reducing. Changes in land use, (in agriculture, road building and building of homes) which destroy or fragment habitats, tourism, commercial uses of particular species and pollution are all reducing biodiversity. As human populations increase, these effects increase.
The huge increases in human population over the last few hundred years has been possible due to the development of intensive farming, including monoculture, selective breeding, huge farms, mechanisation. However, it is apparent that this intensive farming is damaging the environment and is becoming increasingly difficult to sustain.
Monoculture has a major impact on the environment as it involves using a single variety of a crop, and this reduces genetic diversity and renders all crops in a region susceptible to disease. Reduced species diversity has many knock-on effects such as allowing a pest species to get out of control, fewer plants due to the lack of pollinating insects and a loss of species that may be useful to humans. Intensive farming often uses powerful chemicals such as insecticides, rodenticides, fungicides which are used to fight pests and diseases and also unwanted weeds are killed by applying herbicides.
Unfortunately, most of these chemicals are passed onto other plants and animals in food chains. Some fish can be killed by only tiny quantities of herbicides and birds have suffered in a similarly as a result of the use of insecticides. Since nitrate and ammonium ions are very soluble, they do not remain in the soil for long and are quickly leached out, ending up in local rivers and lakes and causing eutrophication.
Eutrophication refers to the effects of nutrients on aquatic ecosystems. The main causes of fertilisers include leaching off farm fields into the surrounding water course, sewage (liquid waste from houses and factories), increased soil erosion as a result of deforestation and drainage of washings from intensive livestock units. Eutrophication causes an increase in the Algae growth (algal-blooms) due to the increased nitrate and phosphate loading. Although the algae do release some oxygen from photosynthesis their dense surface growth cuts down light penetration to the lower depths, reducing the numbers of large rooted plants. There is a general decrease sink to the in the diversity of species not only the plant community but also the animals that rely on them for food and shelter. Dead algae sink to the bottom and are decomposed by aerobic bacteria.
This uses up a lot of dissolved oxygen (producing a high BOD). Oxygen depletion means that many species of invertebrates and fish die. Many food chains collapse. Turbidity increases, the rate of sedimentation increases and also less light penetrates for photosynthesis. These effects can create many problems for humans such as: the water removed for drinking may have an unacceptable taste or odour; the water may be harmful to our health, its value as a conservation area may decrease resulting in the area being less appealing to tourists and also important fisheries may be lost. The diagram below illustrates eutrophication.
Biochemical Oxygen Demand (BOD) measures the rate of oxygen consumption by a sample of water, and therefore gives a good indication of eutrophication. A high BOD means lots of organic material and aerobic microbes, i.e. eutrophication. The method is simple: a sample of water is taken and its O2 concentration is measured using an oxygen meter. The sample is then left in the dark for 5 days at 20C, and the O2 is measured again. The BOD is then calculated by doing the following: original O2 concentration – final O2 concentration. The more oxygen used up over the 5 days (in mg.dm-3) the higher the BOD, and the higher the BOD the more polluted the water is. This table shows some typical BOD values.
Aquatic ecosystems can slowly recover from a high BOD as oxygen dissolves from the air, but long-term solutions depend on reducing the amount of minerals leaching into the water. This can be achieved by applying inorganic fertilisers more carefully, by using organic fertilisers, by using low-phosphate detergents, and by removing soluble minerals by precipitation in modern sewage plants. As a last resort eutrophic lakes can be dredged to remove mineral-rich sediment, but this is expensive and it takes a long time for the ecosystem to recover.
These are chemicals that are applied to soil to provide crops with nutrients; nitrogen in the available form of nitrates is an example of a nutrient essential for plants that can be provided by fertilisers. They are totally different to pesticides. As they are really just a source of nutrients they do not normally have any negative effects on plants and animals. However, some plants can utilise the extra nutrients more effectively than others and therefore out compete the other plants. In this way fertilisers can be responsible for a reduction in species diversity
Inorganic fertilisers are very effective but also have undesirable effects on the environment. Since nitrate and ammonium ions are very soluble, they do not remain in the soil for long and are quickly leached out, ending up in local rivers and lakes and causing eutrophication. They are also expensive.
An alternative solution, which does less harm to the environment, is the use of organic fertilisers, such as animal manure (farmyard manure or FYM), composted vegetable matter, crop residues, and sewage sludge. These contain the main elements found in inorganic fertilisers (NPK), but in organic compounds such as urea, cellulose, lipids and organic acids. Of course plants cannot make use of these organic materials in the soil: their roots can only take up inorganic mineral ions such as nitrate, phosphate and potassium. But the organic compounds can be digested by soil organisms such as animals, fungi and bacteria, who then release inorganic ions that the plants can use. There are many advantages of organic fertilisers such as;
Since the compounds in organic fertilisers are less soluble than those in inorganic fertilisers, the inorganic minerals are released more slowly as they are decomposed. This prevents leaching and means they last longer. The organic wastes need to be disposed of anyway, so they are cheap. Furthermore, spreading on to fields means they will not be dumped in landfill sites, where they may have caused uncontrolled leaching. The organic material improves soil structure by binding soil particles together and provides food for soil organisms such as earthworms. This improves drainage and aeration.
Some disadvantages are that they are bulky and less concentrated in minerals than inorganic fertilisers, so more needs to be spread on a filed to have a similar effect. They may contain unwanted substances such as weed seeds, fungal spores, heavy metals.
Pesticides are used in agriculture to reduce wastage of crops from damage by insects and fungi, and also to kill pests which harm animals, such as the mite which causes sheep scab. Herbicides are used to kill weeds, reducing competition with crop plants and so increasing yields. Like fertilisers, pesticides and herbicides can wash off land on which they are used and can enter water courses, causing problems there as well as on land. Pesticides have to be effective against the pest, but have no effect on the crop. They may kill the pests, or just reduce their population by slowing growth or preventing reproduction. Intensive farming depends completely on the use of pesticides, and some wheat crops are treated with 18 different chemicals to combat a variety of weeds, fungi and insects. In addition, by controlling pests that carry human disease, they have saved millions of human lives. However, with their widespread use and success there are problems, the mains ones being persistence and bioaccumulation.
Both of these are illustrated by DDT (Dichlorodiphenyltrichloroethane), an insecticide used against the malaria mosquito in the 1950s and 60s very successfully, eradicating malaria from southern Europe. However the population of certain birds fell dramatically while it was being used and high concentrations of DDT were found in their bodies, affecting calcium metabolism and causing their egg shells to be too thin and fragile. DDT was banned in developed countries in 1970, and the bird populations have fully recovered. Alternative pesticides are now used instead, but they are not as effective, and continued use of DDT may have eradicated malaria in many more places.
Persistence. This refers to how long a pesticide remains active in the environment. Some chemicals are broken down by decomposers in the soil (they’re biodegradable) and so are not persistent, while others cannot be broken down by microbes (they’re non biodegradable) and so continue to act for many years, and are classed as persistent pesticides. The early pesticides (such DTT) were persistent and did a great deal of damage to the environment, and these have now largely been replaced with biodegradable insecticides such as carbamates and pyrethroids.
Bioaccumulation (or Biomagnification). This refers to the built-up of a chemical through a food chain. DDT is not soluble in water and is not excreted easily, so it remains in the fat tissue of animals. As each consumer eats a large mass of the trophic level below it, DTT accumulates in the fat tissue of animals at the top of the food chain. This food chain shows typical concentrations of DDT found in a food chain (in parts per million, ppm):
The high concentration of DDT in birds explains why the toxic effects of DDT were first noticed in birds.
So why should we maintain diversity? For many ecologists, there is no need to answer this question at all – it is simply obvious that the variety of habitats and living organisms on Earth is not only a delight but also a responsibility, and that we have a moral obligation to care for them. But also there are some practical arguments for maintaining biodiversity. For example, there is evidence that a reduction in biodiversity may reduce climatic stability. Loss in biodiversity in ecosystems may result in drought or flooding in particular areas. Loss of genetic diversity in populations may result in their extinction. Species that we don’t know very much about could be very useful to humans.
Food production is uneven because some parts of the world have a climate more suited to growing crops than others. In countries where crops can be grown, farmers are usually efficient, making use of the latest agricultural techniques. Many of the developing countries cannot finance modern methods of crop production. Crops sometimes fail to climatic reasons such as drought. In other instances crops have been grown only to be eaten by pests such as locusts or ravaged by diseases. For these reasons most people in developed countries are well fed where as malnutrition and starvation are common in the third world.
There must be a balance between food production and food production as the human population is continuously increasing more land is becoming intensively cultivated for food. More and more plants and animals are threatened by reduction in umbers or possible extinction because their natural habitats vanish. It is now estimated that about 25000 different plant species are threatened with extinction. Many ecologists now realise that conservation is essential for the continued survival of the human race.