Human impact on ecosystems

 

                                            HUMAN IMPACTS ON ECOSYSTEM

Now the world is in the computer age. Man has conquered every aspect of life by developing technology, medicine, and agriculture. Today man has reached the maximum height he can go by damaging the environment. Without thinking he is also a part of it man has done great damage to the environment for the sake of development. If he damages the environment he also has to suffer the effect of it.

The impacts of man on the ecosystem can be discussed under the following aspect

Commercialization of agriculture

·     Industrialization

·     Urban expansion

  War

  Exploiting of natural resources

 Pollution of soil, water, and atmosphere

Growing population

 When we think about the commercialization of agriculture every country has to give some percentage of their forests to clear out. When we think about our country the forest coverage is 44% in 1956 but in 1992 it has declined up to 22%. This clearing of forests had done after introducing large-scale projects like Mahaveli. To supply the needs of the grown population of a country like food, fuel, timber, shelter, and other resources many forest, woodland, and scrub were cleared.

Due to this deforestation, many serious problems have arisen. Loss of traditionally harvested products such as timber, fuelwood, honey, fruit, and herbs. Forests catch a large amount of rain. An intact forest canopy softens the impact of heavy tropical rainfall in many ways. It releases a large amount of water back into the atmosphere in evaporation and transpiration and channels water gently through the vegetation to the soil. If the forest canopy is removed tropical soil surface bakes hard in the intense heat. Rainfall cannot easily penetrate and is rapidly lost from the area in surface run-off. And at the same time, flood hazard is created in the plains below. Furthermore rapid run-off of rainwater results in soil erosion. This can remove topsoil and make ground unsuitable for growing crops. It can also lead to silting of reservoirs which reduces their usage time; dams must be continuously dredged to keep them open. In Sri Lanka, to cultivate cash crop cardamom, 2400 hectares were cleared in the Knuckles range. Being hilly areas with a steep slope and also having high rainfall these places are especially susceptible to soil erosion.

The effects of deforestation are very hazardous. Some of them are as follows.

1.  Deforestation increases global carbon dioxide concentration which may have long    term effects on the global climate

2.  Forests have diverse wildlife communities. Their destruction will lead to innumerable extinction of little known forms of life

3. Competition between native and invasive species may occur.

Areas in the Ratnapura district were mined for precious stones. The rainwater collected in these pits makes good breeding places for mosquitoes.

                              When we consider industrialization, we can see that it alters the gaseous content of the atmosphere, and adds harmful things like soot, heat to the air, chemicals to the soil and water. Therefore, industrialization causes pollution of the environment in every way. Now let me define what pollution is?

Pollution: Is the release into the environment of substances or energy in such quantities and for such duration that they cause harm to people or other organisms or their environment.

Pollution can affect all the aspects of the environment that is natural (living and non-living) or man m, made environment.

• Pollution of the atmosphere
• Pollution of water
• Pollution of soil
• Pollution of the atmosphere: The earth’s atmosphere is a mixture of gasses. The lowermost layer of the atmosphere, 10km thick, is the layer that gas exchange occurs between the atmosphere and the living organisms. Above this layer, there is the stratosphere layer which contains the ozone layer. This layer absorbs UV and IR from the sun. Therefore organisms protect from harmful radiations by the Ozone layer. Chlorofluorocarbon (CFC) is one of the harmful gases that destroy the ozone canopy. There are many naturally found gases in the atmosphere and they are incorrect proportions. Industrialization alters this proportion of natural constituents. When we consider the gas carbon dioxide its natural percentage is 0.03% in the atmosphere. But many human activities such as the burning of fuel (coal, oil, and gas) farming of animals will change this proportion by adding carbon dioxide. The earth reflects some of the heat it gained from the sun and cools the atmosphere. When the air has more carbon dioxide than the normal percentage in the atmosphere the reflection of heat will not occur properly because carbon dioxide absorbs some of the heat. So, the part of the heat is not reflected in the space. Due to this heat, global warming may happen and ice caps of the poles will melt out, and rising up of sea levels will occur. One of the consequences of this would be the flooding of large areas of the lowlands where many modern cities are built. For example city of Bangkok.

The other air pollutant gases such as oxides of nitrogen and sulfur dioxide may cause great harm. Bronchitis, pneumonia, and heart failure may cause by inhaling sulfur dioxide with soot and ash. These gas pollutants are released into the atmosphere when fossil fuels are burnt. When raining, sulfur dioxide in the air will dissolve in the water and be converted to sulfate ions. Then “acid rain” occurs and it changes the pH value of the inland water masses like rivers and ponds. This will lead to the death of living things in it. Sulfates can be absorbed by plant roots and plants may be affected by them. On the other hand, small apertures of the plant leaves (stomata) can absorb sulfur dioxide in the air. In Sri Lanka, forests are dying back in Horton plains due to acid rains. Lichens that are sensitive to aerial pollutants can be considered as bio-indicators of aerial pollution.

As a country, we can try to minimize air pollution but we can’t escape from it because air pollutants can be transported in the air to a long-distance through wind currents. So, pollutants can be found in places that are far away from the place where emissions of the pollutant occur. At present, heavy metal lead is considered to be the most serious pollutant in the atmosphere. There is lead in the air we breathe, in the water we drink, and in the food we eat.

Lead in the air: Combustion of petrol in motor vehicles accounts for 80% lead in the air. People who work close to motor vehicles have a higher concentration of lead in their blood. To avoid this now lead-free petrol has been introduced.

Lead in water: Lead in the air is washed by falling rain. Aquatic plant roots absorb lead from their roots. Aquatic animals who are feeding on plants get lead into their bodies. People who feed on these will ingest lead.

Lead in humans: Whether inhaled or ingested lead is absorbed into the bloodstream and accumulates in the liver. When canning food they use lead to seal the containers. This may be added to the food

Water pollution: In Sri Lanka, there is recent evidence for water pollution. The main causes for water pollution are:

• Sewage disposal into the water masses
• Industrial activities
• Commercial agriculture

Sewage is the biggest pollutant of freshwater masses like lakes, ponds, and estuaries. This led to an immediate drop in the amount of oxygen dissolved in the water mass. Organic matter in the sewage will stimulate the microbial population in the water mass, especially bacteria. As they respire they use up oxygen. Further, they use oxygen to the breakdown of organic matter. If the water masses are not flowing (stagnate) this will affect adversely. In polluted lakes, mineral content is higher than that of polluted lakes. Therefore, the polluted water is enriched with minerals and now it is eutrophic and the growth of the phytoplankton is stimulated. Blooms of algae, especially blue-greens quickly appear. Some of the released toxins will kill fish. After some time anaerobic bacteria release gases ammonia, methane, and hydrogen sulfide giving a bad smell and making the water unfit for most forms of aquatic life. Sometimes nitrogen and phosphorus run-offs from fertilizers used in agriculture also will increase the mineral content hence the algal blooms.

Industrial activities may cause chemical pollution and thermal pollution. Major industries in Sri Lanka are

 Milk and food processing

Textile and rubber

Paper and pulp

Tanneries

Formulation of fertilizers and pesticide

Formulation of fertilizers and pesticides

                                      When hot industrial wastes are released into the water masses it will increase the temperature of the water and living creatures could not tolerate that increased temperature. Some heavy metals such as mercury, copper, lead, and zinc may be added to the water masses as by-products of the above industries. These chemicals will give hazardous effects on the living creatures of those water masses as well as on human health.

Commercial agriculture depends on agrochemicals. Agro-chemicals are not naturally found substances and they add to our soil and water bodies then gradually into our bodies causing many unidentifiable diseases. Further, chemical fertilizers, not like organic manure, decrease the quality of the soil such as its texture, microbial content, etc. When we consider agrochemicals pesticides perform a major role in killing pests as well as other natural species which are very important in biological control. Pesticides include insecticides, fungicides, and herbicides. Pesticides have some characteristics that harm the living organisms in the environment. They are as follows,

• Toxicity
• Persistence
• Specificity.

  Toxicity tells about a dose that kills half of an experimental laboratory population of the pest. So, it is very important to apply the correct dosage.

 Persistence is the length of time that pesticide remains in the environment including within the organisms without being broken down.

Specificity: This indicates the most susceptible pests to the pesticide. In our country, most of the farmers are not aware of these things and they use pesticides as they like. The only thing they need is the eradication of the pest population as soon as possible. On the other hand, they should know about the life cycles of the pest. It is much needed to choose the right time to apply the pesticide. Further, they do not take preventive measures to avoid inhaling, ingesting or contacting with pesticides. The farmers when they are spraying pesticides do not wear masks and sometimes do not even cover their bodies. They spray the pesticides on hot and windy days. Wind causes to bring the pesticide all over their bodies. Sweating causes to bring the pesticide in through pores of the skin.

   After spraying the pesticides to the paddy fields they used to wash the spraying tanks in nearby water streams. This causes great harm to the aquatic life of the paddy fields as well as the streams. For example, in those days there were many fish, tadpoles, crabs, snails, and insects like pond skaters, water scorpion unicellular animals like an amoeba, and paramecium as for animals. (That is almost all the animal phyla has represented) Mosses and algae, like Spirogyra, aquatic ferns like Azolla, aquatic flowering plants like aponegetum, pistia also were there in the water streams and in the paddy fields in our village. But alas! Today we can’t see any creature. The same thing has happened to the plant life also that is mosses and algae in the streams and “Gotu kola” and “mukunuvenna” in the fields all are disappeared due to these agrochemicals. 

Effect of pesticides:  1. Directly the species can be affected by eating food with pesticides. 2. When they ate primary or secondary consumers they will be affected secondarily.

This is caused the extinction of some species hence the diversity of species. Among these extinction species, there may be predators of the pests. It prevents the biological control of pests. When we consider decomposers like bacteria and fungi they also may be affected and this reduces the soil fertility. On the other hand nutritious food species also extinct and it is affected the nutrition of village people.

 To avoid the hazardous effect of pesticides can use two main alternatives.                                                              

  1. Biological control: Biological control can be done by introducing natural enemies such as predators, pathogens, and parasites. Sometimes predators of a pest may harm the other important non-pest species. For example, the mongoose which was introduced to Jamaica to control black rats severely reduced some bird populations and caused the extinction of several reptiles.                                                             

2. Integrated control: This method combines and sensitively integrates biological and chemical control. In this method, all the pest controlling methods can be used such as Cultural methods which include crop rotation, mixed cropping, removal of crop residues, using naturally found pesticides such as the juice of Khomba seeds. This will not eradicate the entire pest population but it will keep the pest population below the level of economic in agriculture.