Global Water Pollution

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Hydrological cycle and an Overview of Global Water Pollution

R. NagendranCentre for Environmental studiesAnna University, Chennai 600025

[email protected]

Introduction

The water cycle , also known as the hydrologic cycle , describes the continuous

movement of water on, above and below the surface of the Earth. Since the water

cycle is truly a "cycle," there is no beginning or end. Water can change states among

liquid, vapor, and ice at various places in the water cycle. Although the balance of

water on Earth remains fairly constant over time, individual water molecules can

come and go.

Where is all the Earths water?

Water is the most widespread substance to be found in the natural

environment and it is the source of all life on earth. Water covers 70% of the

earths surface but it is difficult to comprehend the total amount of water whenwe only see a small portion of it. The distribution of water throughout the earth

is not uniform. Some places have far more rainfall than others.

There are many reasons for this, such as where the mountains are and where

the prevailing winds blow. This rainfall distribution partly explains the differences in

vegetation and why some areas are deserts and some are rainforests.


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Water exists in three states: liquid, solid and invisible vapour . It forms the

oceans, seas, lakes, rivers and the underground waters found in the top layers of the

earths crust and soil cover. In a solid state, it exists as ice and snow cover in polar and

alpine regions. A certain amount of water is contained in the air as water vapour,water droplets and ice crystals, as well as in the biosphere. Huge amounts of water are

bound up in the composition of the different minerals of the earths crust and core.

To assess the total water storage on the earth reliably is a complicated problem

because water is so very dynamic. It is in permanent motion, constantly changing

from liquid to solid or gaseous phase, and back again. The quantity of water found in

the hydrosphere is the usual way of estimating the earths water. This is all the free

water existing in liquid, solid or gaseous state in the atmosphere, on the Earths

surface and in the crust down to a depth of 2000 metres. Current estimates are that the

earths hydrosphere contains a huge amount of water - about 1386 million cubic

kilometres. However, 97.5% of this amount exists as saline waters and only 2.5% as

fresh water.

The greatest portion of the fresh water (68.7%) is in the form of ice and

permanent snow cover in the Antarctic, the Arctic and in the mountainous regions.

29.9% exists as fresh groundwaters . Only 0.26% of the total amount of fresh water on

the earth is concentrated in lakes, reservoirs and river system, where it is most easily

accessible for our economic needs and absolutely vital for water ecosystems.

Different Processes connected with water cycle

Precipitation

Condensed water vapor that falls to the Earth's surface. Most precipitationoccurs as rain, but also includes snow, hail, fog drip, and sleet.


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Approximately 505,000 km 3 (121,000 cu mi) of water fall as precipitation each

year, 398,000 km 3 (95,000 cu mi) of it over the oceans.

Canopy interception

The precipitation that is intercepted by plant foliage and eventually evaporates

back to the atmosphere rather than falling to the ground.

Snowmelt

The runoff produced by melting snow.

Runoff

The variety of ways by which water moves across the land. This includes both

surface runoff and channel runoff. As it flows, the water may infiltrate into the

ground, evaporate into the air, become stored in lakes or reservoirs, or be

extracted for agricultural or other human uses.

Infiltration

The flow of water from the ground surface into the ground. Once infiltrated,

the water becomes soil moisture or groundwater.

Subsurface Flow

The flow of water underground, in the vadose zone and aquifers. Subsurface

water may return to the surface (eg. as a spring or by being pumped) or

eventually seep into the oceans. Water returns to the land surface at lower

elevation than where it infiltrated, under the force of gravity or gravity induced

pressures. Groundwater tends to move slowly, and is replenished slowly, so it

can remain in aquifers for thousands of years.
http://en.wikipedia.org/wiki/Vadose_zonehttp://en.wikipedia.org/wiki/Vadose_zone


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Evaporation

The transformation of water from liquid to gas phases as it moves from the

ground or bodies of water into the overlying atmosphere.

The source of energyfor evaporation is primarily solar radiation. Evaporation often implicitly

includes transpiration from plants, though together they are specifically

referred to as evapotranspiration . Total annual evapotranspiration amounts to

approximately 505,000 km 3 (121,000 cu mi) of water, 434,000 km 3

(104,000 cu mi) of which evaporates from the oceans.

Sublimation

The state change directly from solid water (snow or ice) to water vapor.

Advection

The movement of water in solid, liquid, or vapor states through theatmosphere. Without advection, water that evaporated over the oceans could

not precipitate over land.

Condensation

The transformation of water vapor to liquid water droplets in the air, producingclouds and fog .

Transpiration

The release of water vapor from plants into the air. Water vapor is a gas that

cannot be seen.
http://en.wikipedia.org/wiki/Evapotranspirationhttp://en.wikipedia.org/wiki/Evapotranspirationhttp://en.wikipedia.org/wiki/Cloudhttp://en.wikipedia.org/wiki/Foghttp://en.wikipedia.org/wiki/Evapotranspirationhttp://en.wikipedia.org/wiki/Cloudhttp://en.wikipedia.org/wiki/Fog


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What is the Hydrological Cycle?

The values for stored water given above are for natural, static, water storage in

the hydrosphere. It is the amount of water contained simultaneously, on average, over

a long period of time, in water bodies, aquifers and the atmosphere. For shorter time

intervals such as a single year, a couple of seasons or a few months, the volume of

water stored in the hydrosphere will vary as water exchanges take place between the

oceans, land and the atmosphere.

The total amount of water on the earth and in its atmosphere does not change

but show that rain and flowing rivers must be a motion that transfers water in a never-

ending cycle. Oceans, rivers, clouds and rain, all of which contain water, are in a

frequent state of change. This circulation and conservation of earths water as it

circulates from the land to the sky and back again is called the hydrological cycle or

water cycle.

How does the Hydrological Cycle work?

The stages of the cycle are:

Evaporation

Transport

Condensation

Precipitation

Groundwater

Run-off


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Evaporation

Water is transferred from the surface to the atmosphere through evaporation ,

the process by which water changes from a liquid to a gas. The suns heat provides

energy to evaporate water from the earths surface.

Land, lakes, rivers and oceans send up a steady stream of water vapour and

plants also lose water to the air (transpiration).

Transport

The movement of water through the atmosphere, specifically from over the

oceans to over land, is called transport . Some of the earths moisture transport is

visible as clouds, which themselves consist of ice crystals and/or tiny water droplets.

Clouds are propelled from one place to another by the jet stream, surface-based

circulations like land and sea breezes or other mechanisms. However, a typical cloud

1 km thick contains only enough water for a millimetre of rainfall, whereas the

amount of moisture in the atmosphere is usually 10-50 times greater than this.

Condensation

The transported water vapour eventually condenses , forming tiny droplets in clouds.

Precipitation

The primary mechanism for transporting water from the atmosphere to the

surface of the earth is precipitation .

When the clouds meet cool air over land, precipitation, in the form of rain, sleet

or snow, is triggered and water returns to the land (or sea). A proportion of

atmospheric precipitation evaporates.

Groundwater


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Some of the precipitation soaks into the ground and this is the main source of

the formation of the waters found on land - rivers, lakes, groundwater and glaciers.

Some of the underground water is trapped between rock or clay layers - this is

called groundwater . Water that infiltrates the soil flows downward until it encounters

impermeable rock and then travels laterally. The locations where water moves

laterally are called aquifers. Groundwater returns to the surface through these

aquifers , which empty into lakes, rivers and the oceans.

Under special circumstances, groundwater can even flow upward in artesianwells. The flow of groundwater is much slower than run-off with speeds usually

measured in centimetres per day, metres per year or even centimetres per year.

Run-off

Most of the water which returns to land flows downhill as run-off . Some of it

penetrates and charges groundwater while the rest, as river flow, returns to the oceans

where it evaporates. As the amount of groundwater increases or decreases, the water

table rises or falls accordingly. When the entire area below the ground is saturated,

flooding occurs because all subsequent precipitation is forced to remain on the

surface.

Different surfaces hold different amounts of water and absorb water at different

rates. As a surface becomes less permeable, an increasing amount of water remains on

the surface, creating a greater potential for flooding. Flooding is very common during

winter and early spring because frozen ground has no permeability, causing most

rainwater and melt water to become run-off.

This entire process repeats as illustrated in Figure 1.


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Figure 1 Stages of Hydrological cycle

Water Balance

A considerable portion of river flow does not reach the ocean, having

evaporated those areas with no natural surface run-off channels. On the other hand,

some groundwater bypasses river systems altogether and goes directly to the ocean or

evaporates.

Every year, the turnover of water on Earth involves 577,000 km 3 of water. This

is water that evaporates from the ocean surface (502,800 km 3) and from land (74,200

km 3). The same amount of water falls as atmospheric precipitation, 458,000 km 3 on

the ocean and 119,000 km 3 on land. The difference between precipitation and

evaporation from the land surface (119,000 74,200 = 44,800 km 3/year) represents

the total run-off of the Earths rivers (42,700 km 3/year) and direct groundwater run-

off.


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Surface Waters

Rain water searches for the quickest route to the sea and flows into rivers,

streams, lakes and underground stores. The water in the surface waters is clean

enough to support a variety of wildlife. Although it is clean, it is not safe to drink and

needs to be treated in a water treatment works to remove any substances that may be

harmful.

Water Treatment Works

Water is abstracted from underground sources via boreholes or alternatively is

pumped from rivers and stored in reservoirs before being passed through sand filter

beds which trap any dirt and organisms. It is then treated using the most up to date

advanced water treatment (AWT) technology such as ozonation and carbon filtration

(granular activated carbon) which remove the substances that we cannot see.

Water Distribution

Clean, fresh drinking water is pumped into an underground network of pipes

and storage reservoirs and is not seen again until it reaches your tap. This guarantees

that the water you drink remains clean and fresh.

Water Use

On average, in European countries, each person uses around 55,000 litres of water

every year. Baths, showers, washing up, washing clothes and toilet flushing all use

large amounts of water.


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These activities transform clean tap water into dirty wastewater. The water utility not

only supplies clean drinking water but also collects, transports and disposes of the

dirty water after it has been used.

Sewerage

Dirty water or sewage is collected firstly in drains and then in underground sewers and

is transported via a sewerage system (a network of pipes and tunnels) to a sewage

treatment works.

Sewage Treatment Works

These works use natural micro-organisms to remove harmful substances from dirty

water. The solid material (sludge) is separated from the liquid (effluent) and both are

treated to produce clean effluent that can be released back to the river and bio-solids

that can be used in agriculture as a fertilizer or incinerated to produce energy.

Completing the Cycle

The river continues its journey back to the sea where the cycle starts again. Water

evaporates to form clouds, condenses to droplets and eventually falls as rain on to the

ground.


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Water Pollution

Although we as humans recognize the fact that water is essential for everything on our

planet to grow and prosper, we disregard it by polluting our rivers, lakes, and oceans.

Subsequently, we are slowly but surely harming our planet to the point where

organisms are dying at a very alarming rate. In addition to innocent organisms dying

off, our drinking water has become greatly affected as is our ability to use water for

recreational purposes. In order to combat water pollution, we must understand the

problems and become part of the solution.

Point and nonpoint sources of water pollution

According to the American College Dictionary, pollution is defined as: to make foul

or unclean; dirty. Water pollution occurs when a body of water is adversely affected

due to the addition of large amounts of materials to the water. When it is unfit for its

intended use, water is considered polluted. Two types of water pollutants exist; point

source and nonpoint source. Point sources of pollution occur when harmful

substances are emitted directly into a body of water. The major oil spills (E.g., Exxon

Valdez oil spill) best illustrates point source water pollution. A nonpoint source

delivers pollutants indirectly through environmental changes. An example of this type

of water pollution is when fertilizer from a field is carried into a stream by rain, in theform of run-off which in turn affects aquatic life. The technology exists for point

sources of pollution to be monitored and regulated, although political factors may

complicate matters. Nonpoint sources are much more difficult to control. Pollution

arising from nonpoint sources accounts for a majority of the contaminants in streams

and lakes.


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Causes of water pollution

Many causes of pollution including sewage and fertilizers contain nutrients such as

nitrates and phosphates. In excess levels, nutrients over stimulate the growth of aquatic plants and algae. Excessive growth of these types of organisms consequently

clogs our waterways, use up dissolved oxygen as they decompose, and block light to

deeper waters. This, in turn, proves very harmful to aquatic organisms as it affects the

respiration ability or fish and other invertebrates that reside in water.

Pollution is also caused when silt and other suspended solids, such as soil, wash off

plowed fields, construction and logging sites, urban areas, and eroded river banks

when it rains. Under natural conditions, lakes, rivers, and other water bodies undergo

Eutrophication, an aging process that slowly fills in the water body with sediment and

organic matter. When these sediments enter various bodies of water, fish respiration

becomes impaired, plant productivity and water depth become reduced, and aquatic

organisms and their environments become suffocated. Pollution in the form of

organic material enters waterways in many different forms as sewage, as leaves and

grass clippings, or as runoff from livestock feedlots and pastures. When natural

bacteria and protozoan in the water break down this organic material, they begin to

use up the oxygen dissolved in the water. Many types of fish and bottom-dwelling

animals cannot survive when levels of dissolved oxygen drop below two to five parts

per million.

When this occurs, it kills aquatic organisms in large numbers which leads to

disruptions in the food chain.

Pathogens are another type of pollution that proves very harmful. They can cause

many illnesses that range from typhoid and dysentery to minor respiratory and skin

diseases. Pathogens include such organisms as bacteria, viruses, and protozoan.


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These pollutants enter waterways through untreated sewage, storm drains, septic

tanks, runoff from farms, and particularly boats that dump sewage. Though

microscopic, these pollutants have a tremendous effect evidenced by their ability to

cause sickness. The pathways of water contamination are indicated in Figure 3.

Figure 3 The pathways of water contamination

Additional forms of water pollution

Three last forms of water pollution exist in the forms of petroleum, radioactive

substances, and heat. Petroleum often pollutes water bodies in the form of oil,

resulting from oil spills. The previously mentioned Exxon Valdez is an example of

this type of water pollution.


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These large-scale accidental discharges of petroleum are an important cause of

pollution along shore lines. Besides the supertankers, off-shore drilling operations

contribute a large share of pollution. One estimate is that one ton of oil is spilled for every million tons of oil transported. This is equal to about 0.0001 percent.

Radioactive substances are produced in the form of waste from nuclear power plants,

and from the industrial, medical, and scientific use of radioactive materials. Specific

forms of waste are uranium and thorium mining and refining. The last form of water

pollution is heat. Heat is a pollutant because increased temperatures result in the

deaths of many aquatic organisms. These decreases in temperatures are caused when

a discharge of cooling water by factories and power plants occurs.

Classifying water pollution

The major sources of water pollution can be classified as municipal, industrial, and

agricultural. Municipal water pollution consists of waste water from homes and

commercial establishments. For many years, the main goal of treating municipalwastewater was simply to reduce its content of suspended solids, oxygen-demanding

materials, dissolved inorganic compounds, and harmful bacteria. In recent years,

however, more stress has been placed on improving means of disposal of the solid

residues from the municipal treatment processes. The basic methods of treating

municipal wastewater fall into three stages: primary treatment, including grit removal,

screening, grinding, and sedimentation; secondary treatment, which entails oxidation

of dissolved organic matter by means of using biologically active sludge, which is

then filtered off; and tertiary treatment, in which advanced biological methods of

nitrogen removal and chemical and physical methods such as granular filtration and

activated carbon absorption are employed. The handling and disposal of solid

residues can account for 25 to 50 percent of the capital and operational costs of a

treatment plant (Figure 4).


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Figure 4 A schematic of wastewater treatment

The characteristics of industrial waste waters can differ considerably both within

and among industries. The impact of industrial discharges depends not only on their collective characteristics, such as biochemical oxygen demand and the amount of

suspended solids, but also on their content of specific inorganic and organic

substances. Three options are available in controlling industrial wastewater. Control

can take place at the point of generation in the plant; wastewater can be pretreated for

discharge to municipal treatment sources; or wastewater can be treated completely at

the plant and either reused or discharged directly into receiving waters.

Agriculture, including commercial livestock and poultry farming, is the source of

many organic and inorganic pollutants in surface waters and groundwater. These

contaminants include both sediment from erosion cropland and compounds of

phosphorus and nitrogen that partly originate in animal wastes and commercial

fertilizers. Animal wastes are high in oxygen demanding material, nitrogen and

phosphorus, and they often harbor pathogenic organisms.


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Wastes from commercial feeders are contained and disposed of on land; their

main threat to natural waters, therefore, is from runoff and leaching. Control may

involve settling basins for liquids, limited biological treatment in aerobic or anaerobic

lagoons and a variety of other methods.

Global water pollution

Estimates suggest that nearly 1.5 billion people lack safe drinking water and that at

least 5 million deaths per year can be attributed to waterborne diseases. With over 70

percent of the planet covered by oceans, people have long acted as if these very bodies

of water could serve as a limitless dumping ground for wastes. Raw sewage, garbage,

and oil spills have begun to overwhelm the diluting capabilities of the oceans, and

most coastal waters are now polluted. Beaches around the world are closed regularly,

often because of high amounts of bacteria from sewage disposal, and marine wildlife

is beginning to suffer. Perhaps the biggest reason for developing a worldwide effort to

monitor and restrict global pollution is the fact that most forms of pollution do not

respect national boundaries.

The first major international conference on environmental issues was held in

Stockholm, Sweden, in 1972 and was sponsored by the United Nations (UN). This

meeting, at which the United States took a leading role, was controversial because

many developing countries were fearful that a focus on environmental protection was

a means for the developed world to keep the undeveloped world in an economically

subservient position. The most important outcome of the conference was the creation

of the United Nations Environmental Program (UNEP).

Water quality

Water quality is closely linked to water use and to the state of economic

development. In industrialized countries, bacterial contamination of surface water

caused serious health problems in major cities throughout the mid 1800s.


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By the turn of the century, cities in Europe and North America began building sewer

networks to route domestic wastes downstream of water intakes. Development of

these sewage networks and waste treatment facilities in urban areas has expanded

tremendously in the past two decades. However, the rapid growth of the urban population (especially in Latin America and Asia) has outpaced the ability of

governments to expand sewage and water infrastructure. While waterborne diseases

have been eliminated in the developed world, outbreaks of cholera and other similar

diseases still occur with alarming frequency in the developing countries. Since World

War II and the birth of the chemical age, water quality has been heavily impacted

worldwide by industrial and agricultural chemicals. Eutrophication of surface waters

from human and agricultural wastes and nitrification of groundwater from agricultural

practices has greatly affected large parts of the world. Acidification of surface waters

by air pollution is a recent phenomenon and threatens aquatic life in many area of the

world. In developed countries, these general types of pollution have occurred

sequentially with the result that most developed countries have successfully dealt with

major surface water pollution. In contrast, however, newly industrialized countries

such as China, India, Thailand, Brazil, and Mexico are now facing all these issues

simultaneously.

Conclusion

Clearly, the problems associated with water pollution have the capabilities to disrupt

life on our planet to a great extent. Congress has passed laws to try to combat water pollution thus acknowledging the fact that water pollution is, indeed, a serious issue.

But the government alone cannot solve the entire problem. It is ultimately up to us, to

be informed, responsible and involved when it comes to the problems we face with

our water. We must become familiar with our local water resources and learn about

ways for disposing harmful household wastes so they dont end up in sewage

treatment plants that cant handle them or landfills not designed to receive hazardous

materials.


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In our yards, we must determine whether additional nutrients are needed before

fertilizers are applied, and look for alternatives where fertilizers might run off into

surface waters. We have to preserve existing trees and plant new trees and shrubs to

help prevent soil erosion and promote infiltration of water into the soil. Around our houses, we must keep litter, pet waste, leaves, and grass clippings out of gutters and

storm drains. These are just a few of the many ways in which we, as humans, have

the ability to combat water pollution. As we head into the 21st century, awareness

and education will most assuredly continue to be the two most important ways to

prevent water pollution. If these measures are not taken and water pollution

continues, life on earth will suffer severely.

Global environmental collapse is not inevitable. But the developed world must

work with the developing world to ensure that new industrialized economies do not

add to the world's environmental problems. Politicians must think of sustainable

development rather than economic expansion. Conservation strategies have to become

more widely accepted, and people must learn that energy use can be dramatically

diminished without sacrificing comfort. In short, with the technology that currently

exists, the years of global environmental mistreatment can begin to be reversed.

Acknowledgement

This article is based the information sourced from the publications of severalexperts in the field. I wish to acknowledge all the authors.

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Global Water Pollution