1. HUMAN ACTIVITIES AND THE ENVIRONMENT

3. For several thousand years, humans beings have greatly altered the face of the earth more than any other species has ever done. Changes have been done so that human life can be made more comfortable. However, many of these alterations that offer human conveniences have been at the expense of the structure and function of ecosystems.

7. Changes in the landscape One of the ways that man has altered his environment is by physically reshaping the landscape. For example, he may clear away a forest so that he can have a tract of land for planting crops, for buildings, or for roads. Landscape changes also include digging up canals for irrigation or sewage systems, quarrying for mining purposes,

8. constructing underground tunnels for transportation, and erecting dams across rivers. Sometimes, landforms are constructed where they did not use to exist. Examples are artificial hills on golf courses, or dredged-in sand and gravel along riverbanks or shorelines to extend lots for infrastructure. These alterations could have varying effects.

9. Geophysical effects. Among the notable effects of landscape modification are changes in the atmosphere conditions of the region. For example, massive skyscraper may serve as artificial highland barriers in a city plain. They influence the weather by affecting the movement of cold and warm air masses and the frequency and amount of precipitation.

10. Also, concrete pavements and walls of buildings in cities tend to absorbs more heat from the sun, causing air in these areas to be warmer. Human activities related to landscaping can also cause geological hazards, such as landslides, flash floods, or sudden earthquakes in places where they do not typically occur. The removal

11. of trees from slopping mountainsides, deep excavation, or dynamite explosion can trigger these events by hastening large-scale weathering, erosion, or diastrophic movements.

12. Effects on biotic communities Artificial landscaping could also affect the distribution of living things in an ecosystem. Certain land features, such as a deep river or high mountain, serve as natural barriers to the dispersal speed of organisms. Those that cannot surmount these barriers will be confined to a limited area. However, some barriers may serve

13. as avenues of dispersal to other species. Migrating fish, for example, can swim in flowing rivers and travel to favorable spawning sites. Seeds of some plants, such as coconuts that fall to the sea, will be carried off by water currents to other islands where they may more abundantly. When natural barriers or roadway are modified by artificial landscaping, the habitat’s means of dispersal of some

14. species are disrupted. They may no longer suit the needs of affected and sensitive organisms. Their chances of survival in a targeted area are minimized, and their kind may die out in that locality.

16. Environmental pollution The growing number of people, as well as modern technology, has led to the production, usage, and release of more chemicals to the environment at a very rapid rate. The deterioration of the environment resulting from the release of excessive amounts of substances, mostly waste products, into the air, water, and soil is called pollution.

17. Because the quality of life is dependent on the quality of the environment, pollution is also detrimental to living things.

20. kinds of pollutants: Hazardous Nonhazardous

21. 1. Hazardous These materials pose an immediate threat to life even when emitted in relatively low amounts. These include radioactive materials from nuclear plants, highly infective waste products from hospitals or clinics, toxic gases, and heavy metals, such as lead and mercury from some industrial sources.

23. 2. Nonhazardous Such pollutants are not immediately life-threatening, but they may be harmful over a long period of time or in a very large amounts. These includes smoke emission from combustion (especially in motor vehicles), pesticides, house wastes or garbage, sludge, and sewage from water-treatment plants, and synthetic.

24. Spraying pesticides on the fields

25. Dispersal of Pollutants. All materials eventually become part of the geological cycles that circles and spread them all over the world through the movements of wind, water, and soil. Pollutants can be done in the atmosphere, seeped through the ground, or carried off by runoffs and water currents. Even materials buried deep in the earth may be brought out to the open through soil erosion.

26. Because the different physical aspects of the environment are interconnected, any pollutant that contaminates one area will eventually adversely affect another. For example, air pollutants that enter the atmosphere, such as particulates or aerosols from smoke, may be washed out by rain. The pollutants deposited on land may be washed off into bodies of water,

27. including natural reservoirs of drinking water. Thus, even terrestrial or aquatic environments will be exposed to air pollutants. If the rate at which pollutants are released to the environment exceeds the rate in which they are degraded or dissipated (reduced in concentration), they will accumulate in ever-increasing amount.

28. Effects of pollution Health Hazards Effects on biotic communities Oxygen and nutrient depletion

29. 4. Global warming 5. ozone depletion 6. acid rain 7. damage to properties and unsightly surroundings.

30. 1. Health hazards Air pollution inhaled by people can cause respiratory disorders. The intake of contaminated water or exposure to radioactive or infective waste can cause serious illness. In very extreme cases, death may result, especially among the very young or the aged.

31. 2. Effects on biotic communities The entry of pollutants in natural environment retards the growth and threatens the physiological states of plants and animals. Even when health disorders are not yet manifested among humans, large numbers of deaths in biotic communities not targeted by pest control measures are alarming indications of severe pollution.

32. 3. Oxygen and Nutrient depletion Large amounts of non hazardous pollutants, such as sludge or sewage, can increase the rates of algal decay in bodies of water. These result in the rapid depletion of the supply of dissolved oxygen for other organisms in the water.

33. Excessive amounts of fertilizers added to the soil hinder the ability of the bacteria to decompose complex organic materials into simpler nutrients. Thus, the natural production of soil nutrients for plants is reduced.

34. 4. Global warming The warming of the surface of the earth is due to the presence of gases in the atmosphere that prevent heat from escaping into the space. This is called the greenhouse effect. Pollution coming mostly from the burning of fuels in many parts of the world contribute to global warming

35. 5. Ozone depletion Commonly used aerosol sprays and refrigerants contain chlorofluorocarbons ( CFC’s ). These compounds, when released in the atmosphere, can degrade the ozone layer in the stratosphere. Harmful ultraviolet rays from the sun are screened out by the ozone layer.

36. It’s depletion is most evident in the Antartic regions. The depletion of the ozone layer can lead not only to higher incidences of skin cancers and genetic disorders, but also to reduced numbers of light- sensitive phytoplanktons, the primary producers of the aquatic ecosystem.

37. 6. Acid rain The reactions of industrial pollutants, like sulfur dioxide and nitric acids, with water vapor in the air results in a form of precipitation called acid rain. The corrosive properties of the pollutants in acid rain make it a health hazard. It can also increase the acidity of the soil and water where it is deposited.

38. 7. Damages to properties and unsightly surroundings. Pollutants can chemically react with the structural materials of buildings, roads, ornamental statues, and even textiles, causing them to deteriorate rapidly. Dump sites overflow with solid wastes, sewage- filled canals or litter in the streets reduce the aesthetic values of our surroundings.

39. Regulation of living populations Groups of organisms belonging to the same species in a community are called populations. The size of a population increase through immigration, or the entry of individuals into a particular locality. Individuals that give birth to more offspring also increase the size of the population in that place. However, deaths can slow down continuous

40. population growth. A quantitative measure of population size is population density, the number of individuals of the same species that occupy a given amount of space. Organisms migrate and settle in places where food supply and living spaces are abundant. Birth rates in the population that gather in these places tend to be high because the

41. environment may increase geometrically but not indefinitely. Its numbers could fluctuate between high and low levels because of occasional external influences that check its continuous growth. Among these are geological events, such as weather disturbances and natural disasters, like floods, earthquakes or fires; the spread of diseases; and the presence of parasites.

42. Even if outside checks on local population do not exist, population growth will still be limited by the negative interactions of individual among themselves. The often happens when unchecked populations growth results in crowding. When population density is increased, the amount of food and living space that can be alloted to each

43. individual is reduced – some more so than others. Because increasingly large numbers of individuals are crammed in a small area, it may lead to frequent and intense competition for limited space and food supplies among individuals. This kind of interaction produces serious physical and social stresses on the individual.

44. Stunted growth, reduced reproductive potential, and higher susceptibility to sickness and death are some of the effects of crowding stresses. The same stresses also contribute to higher emigration rates. Some individuals are pressured to move out and seek other hospitable habitats. Thus, the population will tend to decrease until such time when crowding stresses are lessened considerably.

45. Nature finds a way to maintain a balance in the numbers of species occupying a community. This natural balance enables biotic communities to recover from the pressures of overpopulation or large population losses. The overall diversity which adds to the richness of an ecosystem is maintained.

46. However, mankind has had a considerable impact on the natural regulation of local populations. Extensive hunting, overfishing, pest control, had clearing and waste emissions are some human actions that have interfered with the way biotic communities maintain stable and diverse populations. Let us suppose a riceplanter who regards snakes as menaces wants to get rid these reptiles

47. Getting rid of the snakes from a ricefield may lead to an increased population of field mice in the same area. Because there are no predators which will check their numbers, too many mice will overgraze the ricefield or eventually invade granaries and storehouses for food. Thus, human interference on the biotic community has one kind of menace for another.

48. A better understanding of how man affects the biosphere is essential for his long-term survival on earth. All of us depend on nature for our basic needs. The harmful effects of human actions should be countered by efforts to improve the quality of the natural environment.