pollution occurs when a body of water is adversely affected due to the
addition of large amounts of materials to the water. The sources of water
pollution are categorized as being a point source or a non-source point
of pollution. Point sources of pollution occur when the polluting substance
is emitted directly into the waterway. A pipe spewing toxic chemicals directly
into a river is an example. A non-point source occurs when there is runoff
of pollutants into a waterway, for instance when fertilizer from a field
is carried into a stream by surface runoff.
Types of Water Pollution
-- A toxic substance is a chemical pollutant that is not a naturally occurring
substance in aquatic ecosystems. The greatest contributors to toxic pollution
are herbicides, pesticides and industrial compounds.
-- Organic pollution occurs when an excess of organic matter, such as manure
or sewage, enters the water. When organic matter increases in a pond, the
number of decomposers will increase. These decomposers grow rapidly and
use a great deal of oxygen during their growth. This leads to a depletion
of oxygen as the decomposition process occurs. A lack of oxygen can kill
aquatic organisms. As the aquatic organisms die, they are broken down by
decomposers which leads to further depletion of the oxygen levels.
A type of organic pollution can
occur when inorganic pollutants such as nitrogen and phosphates accumulate
in aquatic ecosystems. High levels of these nutrients cause an overgrowth
of plants and algae. As the plants and algae die, they become organic material
in the water. The enormous decay of this plant matter, in turn, lowers
the oxygen level. The process of rapid plant growth followed by increased
activity by decomposers and a depletion of the oxygen level is called eutrophication.
-- Thermal pollution can occur when water is used as a coolant near a power
or industrial plant and then is returned to the aquatic environment at
a higher temperature than it was originally. Thermal pollution can lead
to a decrease in the dissolved oxygen level in the water while also increasing
the biological demand of aquatic organisms for oxygen.
-- Ecological pollution takes place when chemical pollution, organic pollution
or thermal pollution are caused by nature rather than by human activity.
An example of ecological pollution would be an increased rate of siltation
of a waterway after a landslide which would increase the amount of sediments
in runoff water. Another example would be when a large animal, such as
a deer, drowns in a flood and a large amount of organic material is added
to the water as a result. Major geological events such as a volcano eruption
might also be sources of ecological pollution.
Specific Sources of Water Pollution
Farms often use large amounts of herbicides
and pesticides, both of which are toxic pollutants. These substances are
particularly dangerous to life in rivers, streams and lakes, where toxic
substances can build up over a period of time.
Farms also frequently use large amounts
of chemical fertilizers that are washed into the waterways and damage the
water supply and the life within it. Fertilizers can increase the amounts
of nitrates and phosphates in the water, which can lead to the process
Allowing livestock to graze near water
sources often results in organic waste products being washed into the waterways.
This sudden introduction of organic material increaces the amount of nitrogen
in the water, and can also lead to eutrophication.
Four hundred million tons of soil are
carried by the Mississippi River to the Gulf of Mexico each year. A great
deal of this siltation is due to runoff from the exposed soil of agricultural
fields. Excessive amounts of sediment in waterways can block sunlight,
preventing aquatic plants from photosynthesizing, and can suffocate fish
by clogging their gills.
Clearing of land can lead to erosion
of soil into the river.
Waste and sewage generated by industry
can get into the water supply, introducing large organic pollutants into
Many industrial and power plants use
rivers, streams and lakes to despose of waste heat. The resulting hot water
can cause thermal pollution. Thermal pollution can have a disasterous effect
on life in an aquatic ecosystem as temperature increaces decreace the amount
of oxygen in the water, thereby reducing the number of animals that can
Water can become contaminated with
toxic or radioactive materials from industry, mine sites and abandoned
hazardous waste sites.
Acid precipitation is caused when the
burning of fossil fuels emits sulfur dioxide into the atmosphere. The sulfur
dioxide reacts with the water in the atmosphere, creating rainfall which
contains sulfuric acid. As acid precipitation falls into lakes, streams
and ponds it can lower the overall pH of the waterway, killing vital plant
life, thereby affecting the whole food chain. It can also leach heavy metals
from the soil into the water, killing fish and other aquatic organisms.
Because of this, air pollution is potentially one of the most threatening
forms of pollution to aquatic ecosystems.
Sewage generated by houses or runoff
from septic tanks into nearby waterways, introduce organic pollutants that
can cause eutrophication.
Fertilizers, herbicides and pesticides
used for lawn care can runoff and contaminate the waterway. As with agriculteral
fertilizers, home fertilizers can lead to the eutrophication of lakes and
Improper disposal of hazardous chemicals
down the drain itroduce toxic materials into to the ecosystem, contaminating
the water supplies in a way that can harm aquatic organisms.
Leaks of oil and antifreeze from a
car on a driveway can be washed off by the rain into nearby waterways,