Water pollution is the contamination or adverse alteration of the quality of water. Any condition leading to an adverse alteration in water quality is described as water pollution. Water pollution can be effected by a variety of substances such as poisons, sewage, refuse, etc.
Both surface water and ground water can be polluted. Ground water pollution occurs when poisonous substances or contaminants (mainly poisons and sewage) come in contact with aquifer (water table).
Ground water is not exposed, as such sources of its pollution are difficult to categorize. Surface water which is exposed can however be polluted from either point sources or non point sources.
Water is said to be polluted from a point source when contaminants are let into it from one specific inlet. This specific inlet could be a pipe or other flow channel in channels. Chemical effluent from an industry, leakage from a sewage treatment plant or septic tank may constitute point sources of water pollution.
Non point sources
Non point source pollution of water is a diffusion of contaminants into water from no specified individual inlet. It entails leaching of such contaminants into water through relatively larger or spread out surface area. Examples include the herbicides and pesticides carried along in run off to water bodies, leaching of nitrogen compounds from fertilized agricultural land, etc.
Eutrophication is the process by which a body of water acquires a high concentration of nutrients, especially phosphates and nitrates. It promotes excessive algal bloom, which raises the biological oxygen demand in aquatic systems as algae die and decompose. (Art 1993).
Pronounced dissolved oxygen depletion as well as increased concentrations of toxic by products of organic matter decay such as ammonia, hydrogen sulphide may result from eutrophication. “Self shading” is also an aftermath of eutrophication.
Self shading is said to be, when excess phytoplankton in a water body prevents penetration of light to lower depths of the water, such that photosynthesis stops and dissolved oxygen shortage occurs at such depths. This sudden shade of light away from existing phytoplankton at such levels causes more phytoplankton die off.
As plankton die in excess, their decay may cause organic matter pollution in water and result in other chemical changes far from desirable.