WATER POLLUTION AND ITS MAJOR SOURCES, ITS

EFFECT ON VEGETATION

DEFINITION OF WATER POLLUTION:-

Water pollution can be defined as “ presence of solid, liquid and
gaseous contaminants in such concentration that may alter the quality of water”.
Actually water pollution is the contamination of water bodies usually as a result of human
activities. Water bodies include for example lakes, rivers, oceans, aquifers and groundwater.
Water pollution results when contaminants are introduced into the natural environment. Water is
one of the renewable resources essential for sustaining all forms of life, food production,
economic development, and for general well being. It is impossible to substitute for most of its
uses, difficult to de pollute, expensive to transport, and it is truly a unique gift to mankind from
nature. Water is also one of the most manageable natural resources as it is capable of diversion,
transport, storage, and recycling. All these properties impart to water its great utility for human
beings. The surface water and groundwater resources of the country play a major role in
agriculture, hydropower generation, livestock production, industrial activities, forestry, fisheries,
navigation, recreational activities etc.

SOURCES OF WATER POLLUTION:-

Water pollution can occur from two sources. 1. Point source and 2. Non-point source . Point
sources of pollution are those which have direct identifiable source. Example includes pipe
attached to a factory, oil spill from a tanker, effluents coming out from industries. Point sources
of pollution include wastewater effluent (both municipal and industrial) and storm sewer
discharge and affect mostly the area near it. Whereas non-point sources of pollution are those
which arrive from different sources of origin and number of ways by which contaminants enter
into groundwater or surface water and arrive in the environment from different non identifiable
sources. Examples are runoff from agricultural fields, urban waste etc. Sometimes pollution that
enters the environment in one place has an effect hundreds or even thousands of miles away.
This is known as transboundary pollution. One example is the radioactive waste that travels
through the oceans from nuclear reprocessing plants to nearby countries. Water pollutants may
be i)Organic and ii)Inorganic water pollutant.
1. Organic water pollutants: They comprise of insecticides and herbicides, organohalides and
other forms of chemicals; bacteria from sewage and livestocks farming; food processing wastes;
pathogens; volatile organic compounds etc.
2. Inorganic water pollutants: They may arise from heavy metals from acid mine drainage; silt
from surface run-off, logging, slash and burning practices and land filling; fertilizers from
agricultural run-off which include nitrates and phosphates etc. and chemical waste from
industrial effluents.
The principle sources of water pollution resulting from exploration and production
operations are:
 Domestic waste
 Sewage waste
 Solid waste
 Industrial waste
 Acid rain
 Oil industry
 Aquatic plants
 Hazardous waste
 Agricultural waste

Sewage and other oxygen demanding waste:-

Management of solid waste is not successful due to huge volumes of organic and non-
biodegradable wastes generated daily. As a consequence, garbage in most parts of India is
unscientifically disposed and ultimately leads to increase in the pollutant load of surface and
groundwater courses. Sewage can be a fertilizer as it releases important nutrients to the
environment such as nitrogen and phosphorus which plants and animals need for growth.
Chemical fertilizers used by farmers also add nutrients to the soil, which drain into rivers and
seas and add to the fertilizing effect of the sewage. Together, sewage and fertilizers can cause a
massive increase in the growth of algae or plankton that facilitate huge areas of oceans, lakes, or
rivers creating a condition known as algal bloom thereby reducing the dissolved oxygen content
of water and killing other forms of life like fish.

Industrial Wastes:
Many of the industries are situated along the banks of river such as steel and paper industries for
their requirement of huge amounts of water in manufacturing processes and finally their wastes
containing acids, alkalies, dyes and other chemicals are dumped and poured down into rivers as
effluents. Chemical industries concerning with manufacture of Aluminium release large amount
of fluoride through their emissions to air and effluents to water bodies. Fertilizer industries
generate huge amount of ammonia whereas steel plants generate cyanide. Chromium salts are
used in industrial process for the production of sodium dichromate and other compounds
containing chromium. All such discharges finally arrive at water bodies in the form of effluents
affecting human health and the organism living there.

Agro-chemical Wastes: In the agricultural sector, water and electricity for irrigation are
subsidized for political reasons. This leads to wasteful flood irrigation rather than adoption of
more optimal practices such as sprinkler and drip irrigation. Cropping patterns and farming
practices also do not necessarily encourage the judicious use of water. There are losses of water
due to breaches and seepage resulting in water logging and salinity. Agro-chemical wastes
include fertilizers, pesticides which may be herbicides and insecticides widely used in crop fields
to enhance productivity. Improper disposal of pesticides from field farms and agricultural
activities contributes a lot of pollutants to water bodies and soils. Some of the pesticides are:
DDT, Aldrin, Dieldrin, Malathion, Hexachloro Benzene etc. Pesticides reach water bodies
through surface runoff from agricultural fields, drifting from spraying, washing down of
precipitation and direct dusting and spraying of pesticides in low lying areas polluting the water
quality. Most of them are non-biodegradable and persistent in the environment for long period of
time. These chemicals may reach human through food chain leading to biomagnification.
Nutrient enrichment:
The sources of nutrients in surface water can be divided broadly into natural and anthropogenic
types. Contribution to pollution by natural source is low due to balance established by the natural
system between the production and consumption of nutrients over the course of time.
Anthropogenic sources of contaminants are contributed from agriculture, domestic and industrial
wastes. Nutrient concentrations in streams and rivers have been strongly correlated with human
land use and disturbance gradients. Both N and P enrichment have links with the agricultural
and urban land uses in the watershed

Oil spillage: Oil discharge into the surface of sea by way of accident or leakage from cargo
tankers carrying petrol, diesel and their derivatives pollute sea water to a great extent.
Exploration of oil from offshore also lead to oil pollution in water. The residual oil spreads over
the water surface forming a thin layer of water-in-oil emulsion.

Acid rain pollution:

Water pollution that alters a plant’s surrounding pH level, such as due to acid rain, can harm or
kill the plant. Atmospheric Sulfur dioxide and nitrogen dioxide emitted from natural and human-
made sources like volcanic activity and burning fossil fuels\interact with atmospheric chemicals,
including hydrogen and oxygen, to form sulfuric and nitric acids in the air. These acids fall down
to earth through precipitation in the form of rain or snow. Once acid rain reaches the ground, it
flows into waterways that carry its acidic compounds into water bodies. Acid rain that collects in
aquatic environments lowers water pH levels and affects the aquatic biota.

. Radioactive waste:
Radioactive pollution is caused by the presence of radioactive materials in water. They are
classified as small doses which temporary stimulate the metabolism and large Doses which
gradually damage the organism causing genetic mutation. Source may be from radioactive
sediment, waters used in nuclear atomic plants, radioactive minerals exploitation, nuclear power
plants and use of radioisotopes in medical and research purposes.

Introduction of Alien species

In some parts of the world, alien species also known as invasive species are a major problem of
water pollution. Outside their normal environment, they have no natural predators, so they
rapidly spread and dominate the animals or plants that thrive there. Common examples of alien
species include zebra mussels in the Great Lakes of the USA, which were carried there from
Europe by ballast water (waste water flushed from ships). The Mediterranean Sea has been
invaded by a kind of alien algae called Caulerpa taxifolia.

Effect of water pollution on plants

The following are the effects of water pollution on plants:

i. Effects of acid deposition:

Many of the gases from acid, aerosols and other acidic substances released into the atmosphere
from industrial or domestic sources of combustion from fossil fuels finally fall down to ground
and reach the water bodies along with run-off rainwater from polluted soil surfaces thereby
causing acidification of water bodies by lowering its pH . In many countries chemical substances
like sulphates, nitrates and chloride have been reported to make water bodies such as lakes, river
and ponds acidic.

ii. Nutrient deficiency in aquatic ecosystem: Population of decomposing

microorganisms like bacteria and fungi decline in acidified water which in turn reduces the rate
of decomposition of organic matter affecting the nutrient cycling. The critical pH for most of the
aquatic species is 6.0. The diversity of species decline below this pH whereas the number and
abundance of acid tolerant species increases. Proliferation of filamentous algae rapidly forms a
thick mat at the initial phase of the acidification of water. Diatoms and green algae disappear
below pH 5.8. Cladophora is highly acid tolerant species and is
abundant in acidic freshwater bodies. Macrophytes are generally absent in acidic water as their
roots are generally affected in such water resulting in poor plant growth. Potamogeton pectinalis
is found in acidified water. It is observed that plants with deep roots and rhizomes are less
affected while plants with short root systems are severely affected in acidic water.

iii. Effects of organic matter deposition: Organic matter from dead and
decaying materials of plants and animals is deposited directly from sewage discharges and
washed along with rainwater into water bodies causing increase in decomposers / microbes such
as aerobic and anaerobic bacteria. Rapid decomposition of organic matter increase nutrient
availability in water favouring the luxuriant growth of planktonic green and blue-green algal
bloom. In addition many of the macrophytes like Salvinia, Azolla, Eicchhornia etc. grow rapidly
causing reduced penetration of light into deeper layer of water body with gradual decline of the
submerged flora . This condition results in reducing the dissolved Oxygen and increase in the
biological oxygen demand (B.O.D). The B.O.D of unpolluted fresh water is usually below 1mg/l
while that of organic matter polluted water is more than 400 mg/l.
 iv. Effects of detergent deposition: Detergents from domestic and industrial uses
wash down into water bodies causing serious effects on plants. Detergents contain high
phosphates which results in phosphate-enrichment of water. Phosphates enter the plants through
roots or surface absorption causing retarded growth of plants, elongation of roots, carbon
dioxide fixation, photosynthesis, cation uptake, pollen germination and growth of pollen tubes,
destruction of chlorophylls and cell membranes and denaturation of proteins causing enzyme
inhibition in various metabolic processes.

v. Effects of agricultural chemicals: Chemicals from fertilizers, pesticides,

insecticides, herbicides etc. applied to crops in excess are washed away with rainwater as runoff,
then enter into soil and finally arrive at the water bodies. Chemicals from fertilizers result in
eutrophication by enrichments of nutrients. Ammonium from fertilizers is acidic in nature
causing acidification of water. Similarly pesticides, herbicides and insecticides also cause change
in pH of the water bodies. Most common effect of these substances is the reduction in
photosynthetic rate. Some may uncouple oxidative phosphorylation or inhibit
nitrate reductase enzyme. The uptake and bioaccumulation capacities of these substances are
great in macrophytic plants due to their low solubility in water.

vi. Effects of industrial wastes: Effluents from industries contain various organic and
inorganic waste products. Fly ash form thick floating cover over the water thereby reducing the
penetration of light into deeper layers of water bodies. Fly ash increases the alkalinity of water
and cause reduced uptake of essential bases leading to death of aquatic plants. Liquid organic
effluents change the pH of water and the specific toxicity effects on the aquatic plants vary
depending on their chemical composition. There may be synergistic, additive or antagonistic
interactions between metals with respect to their effects on plants however these effects are
reduced in hard and buffered freshwater bodies.

vii. Effects of silt deposition: Deposition of silt in water bodies occurs as a result of
erosion carrying silt laden water and due to flood. It increases the turbidity of water and
reduces light penetration in deep water causing decline in abundance of submerged plants.
Siltation inhibits the growth of aquatic plants. Abundance of phytoplankton is affected due to
reduction in surface exchange of gases and nutrients. Plants that are tolerant to turbidity are
abundant followed by those that are intermediate and the least tolerant species. Plants such as
Polygonum, Sagittaria etc. are found to grow in dominance.

viii. Effects of oil spillage: Oil pollution due to spillage of oil tankers and storage
containers prevents oxygenation of water and depletes the oxygen content of the water body by
reducing light transmission inhibiting the growth of planktons and photosynthesis in
macrophytes.

ix. Effects of thermal pollution: The release of heated water into water bodies from
the thermal power plants has an adverse effect on the aquatic life. It reduces the activity of
aerobic decomposers due to oxygen depletion because of high temperature. With decreased
organic matter decomposition , the availability of nutrients in the water bodies is jeopardised.
Aquatic plants show reduced photosynthesis rate due to inhibition of enzyme activity with
increased temperature. Primary productivity and diversity of aquatic plant species decline
because of increased temperature of water bodies as a result of thermal pollution.

x. Effect of nutrient enrinchement: Nutrient enrichment in aquatic water bodies

leads to eutrophication which is a process whereby water bodies receive excess inorganic
nutrients, especially N and P, stimulating excessive growth of plants and algae. Eutrophication
can happen naturally in the course of normal succession of some freshwater ecosystems.
However, when the nutrient enrichment is due to the activities of humans, it is referred to as
“cultural eutrophication”, where the rate of nutrient enrichment is greatly intensified.
Eutrophication was recognized as a pollution problem in North American lakes and reservoirs in
the mid 20th century (Rohde, 1969). Plants must take in nutrients from the surrounding
environment inorder to grow. Nitrogen and phosphorous, in particular, encourage growth
because they stimulate photosynthesis. This is why they are common ingredients in plant
fertilizers. When agricultural runoff pollutes waterways with nitrogen and phosphorous rich
fertilizers, the nutrient-enriched waters often paves way to algal bloom leading to
eutrophication.The result is oxygen depletion and dying of fishes due to suffocation.

xi. Phytotoxicity effects on plants: When chemical pollutants build up in aquatic

or terrestrial environments, plants can absorb these chemicals through their roots. Phytotoxicity
occurs when toxic chemicals poison plants. The symptoms of phytotoxicity on plants include
poor growth, dying seedlings and dead spots on leaves. For example, mercury poisoning which
many people associate with fish can also affect aquatic plants, as mercury compounds build up in
plant roots and bodies result in bioaccumulation.As animals feed on polluted food the
increasing levels of mercury is built up through food chain