Water Pollution

Water pollution is the addition of undesirable materials into aquatic bodies, which may cause physical, chemical or biological changes in water, leading to different harmful effects on organisms or making water sources undesirable for use.

One of the problems caused by water pollution are eutrophication and algal bloom. Eutrophication is the enrichment of water bodies with inorganic nutrients, typically nitrates and phosphates. Resulting algal bloom where water bodies become densely populated with phytoplankton. Eutrophication is mainly caused by human activities. Heavy applications of fertilizers on agricultural land leading to the wash away of excessive fertilizers by rain water into rivers or lakes. Also, the manipulation of soil in ploughing, road building and reclamation may also speed up the leaching of inorganic nutrients into water bodies. The wastes of humans and livestock that are rich in nitrogen-containing compounds will be broken down into ammonia and then nitrate. Further, the phosphate-rich detergents and washing powder in sewage are also the food sources of phytoplankton. However, algal bloom is caused by a combination of various factors such as sunlight intensity, availability of nutrients, salinity, water temperature and water flow. Nutrients are accumulated in winter because the temperature and light intensity is low for photosynthetic organisms to consume. So in spring when the temperature and light intensity increase with the nutrient rich water causes the rapid growth of phytoplankton leading to algal bloom.

Algal bloom leads to a number of environmental problems especially on aquatic life. First of all, large amount of floating phytoplankton produces a great quantity of oxygen during daytime, the amount of dissolved oxygen will be greatly reduced during respiration at night time and on cloudy days. Also, the thick mat of floating phytoplankton diminishes the amount of light penetrating the water. Which affects the photosynthesis of submerged plants, further decreases the oxygen content in water. The massive and sudden death of algae due to the rapid exhaustion of nutrients, leading to decomposition of the large amount of dead phytoplankton by microorganisms consuming large quantity of dissolved oxygen in water. All of the above effects lead to the decrease in the content of dissolved oxygen in water. This will lead the death and suffocation of fish and other aquatic organisms. It also disturbs the food chain of aquatic life affecting the aquatic ecosystem.

Inadequate treatment of sewage will lead to deterioration of water quality and microbial hazards. Inadequate treatment of sewage before disposal to aquatic bodies, results in various physical, chemical and biological changes of water. The discharge of sewage may introduce a high level of organic nutrients and bacterial population into water bodies. The decomposition of organic wastes by microorganisms leads to an increase in biological oxygen demand. The dissolved oxygen in the water bodies will decrease dramatically. Ammonia present in the sewage will be converted to nitrates by the action of nitrifying bacteria. Nitrates cause the growth of phytoplankton in water. The great increase in nitrate contents will lead to an increase in its population to a considerable level. If the discharge of sewage is continuing and persistent, microorganisms will use up almost all the dissolved oxygen for decomposition of organic wastes. The lack of oxygen will thus induce the incomplete decomposition process by anaerobic bacteria may produce gases with unpleasant smells such as ammonia and hydrogen sulphide. The depletion of oxygen also leads to the death of most aquatic organisms due to suffocation. The accumulation of their dead bodies further brings anaerobic decomposition, which makes the condition even worse. The combination of low oxygen content, anaerobic decomposition and poisonous gas production makes water septic and dangerous to health. It also renders the water unsuitable for drinking and other purposes. Therefore, sewage treatment is important in controlling water pollution. Also, detergents are present in some of the sewages. They have a number of harmful effects on aquatic life. Some detergents are biodegradable, and have high phosphate content and can lead to algal bloom. Many detergents are non-biodegradable and persist in water. They mix with water and form foams that blanket the water, preventing light penetrating and therefore reduce the rate of photosynthesis of producers in water. it also prevent the entry of oxygen into the water from the atmosphere and reducing the dissolved oxygen content in water.