Water Pollution

1) Water Cycle

Water Cycle

The different water sources of the earth get their water supply from precipitation, while this precipitation in itself is the evaporation from these sources. Water is lost to the atmosphere as vapour from the earth; it condenses and then precipitates back in the form of rain, snow, hail, dew, frost or sleet. This is the hydrologic cycle that continues forever thereby maintaining a balance between the two.

2) Fresh Water

• Rivers

Rivers

Most ancient civilizations grew along the banks of rivers. Even today, millions of people all over the world live on the banks of rivers and depend on them for their survival.

All of us have seen a river - large or small, either flowing through our town, or somewhere else. Rivers are nothing more than surface water flowing down from a higher altitude to a lower altitude due to the pull of gravity. One river might have its source in a glacier, another in a spring or a lake. Rivers carry dissolved minerals, organic compounds, small grains of sand, gravel, and other material as they flow downstream. Rivers begin as small streams, which grow wider as smaller streams and rivers join them along their course across theland. Eventually they flow into seas or oceans. Most rivers With the exception of the Nile, flow towards the Equator. The flow in most rivers is not uniform, which means that sometimes there are floods and sometimes no water flows in them. Flood control projects attempt to reduce the variation in flow.

Unfortunately most of the world's major rivers are heavily polluted, but two of the world's largest river systems-the Amazon, that drains a vast area of South America and the Congo in sub-Saharan Africa- remain relatively healthy. This is because both have few industries and a small human population in their watersheds.

Some facts about rivers

• The Nile, 6695 km long, and the Amazon 6437 km long, are the world's two longest rivers. Sometimes, measurements of their lengths can vary according to the criteria used for measurement.
• An Arab philosopher and physician Avicenna suggested, nearly 1000 years ago, that landscapes changed largely as a result of the action of running water. His views were largely ignored until the 16th century.
• The longest river in Asia is the Yangtze, which is 5472 km long.
• The world's highest waterfall are the Angel Falls in Venezuela, 979 m high, over 780 m of which is an uninterrupted drop.

Rivers in India

India has a large number of rivers that are lifelines for the millions living along their banks. These rivers can be categorized into four groups:

• Rivers that flow down from the Himalayas and are supplied by melting snow and glaciers. This is why these are perennial, that is, they never dry up during the year.
• The Deccan Plateau rivers, which depend on rainfall for their water .
• The coastal rivers, especially those on the west coast, which are short and do not retain water throughout the year.
• The rivers in the inland drainage basin of west Rajasthan, which depend on the rains. These rivers normally drain towards silt lakes or flow into the sand.

The major rivers in India are described here:

• Ganga

  This is considered the holiest of all the great rivers of India. It has its source at the Gangotri glacier, where it flows from the cave Goumukh, as the Bhagirathi, which then joins the River Alaknanda as it flows towards Devaprayag. The largest tributary of the river is the Ghaghara, which flows from the northern Nepal region and joins it before Patna in Bihar. Another major tributary is the Yamuna originating in the Yamunotri glacier, and flows through Delhi and Agra. Others are the Gomti, Gandak, Son, Kosi, Chambal, Sarda, etc. The Ganga is the lifeline for more than 500 million people living along its banks. The water of the river Ganges is considered so sacred that people keep it in their homes for use in prayers on important occasions such as at the time of death. Most cities along the river do not have sewage treatment plants and those that do have them can handle only part of the waste water. Millions of tonnes of untreated sewage are dumped daily into the river from the cities that lie along its banks. Bathing and washing also contribute to the pollution as most of the soap that is used is made from chemical substances. The river is also polluted by human and animal faeces. Industrial units that lie along the banks of the river discharge all the waste into the river and only a few of them have proper treatment facilities.

• Yamuna

  Rising from the Yamunotri glacier in the Tehri Garhwal District in the Himalayas, the Yamuna flows for about 1380 km almost parallel to the Ganga till they meet at Allahabad. It flows through a number of important towns, Delhi, Mathura, Brindaban, and Agra to name some. Since ancient times, the Doab region, where the Ganga and the Yamuna flow, has been considered one of the most fertile areas in the subcontinent. Today however, this majestic river is polluted with domestic waste, silt, and industrial waste. The 22-km stretch between Wazirabad and the Okhla barrage in Delhi is only 2% of the catchment area, but it contributes about 80% of the river's total pollution load. The Hindon Canal also discharges waste from Uttar Pradesh in this stretch. Among the many casualties are birds and fish. There was a time when bird watchers had identified as many as 30 species of birds near the Yamuna, many of them exotic, such as the red-crested pochard and the godwit.

• Brahmaputra

  This mighty river rises in western Tibet in the Manasarovar region. It flows eastwards through the Himalayas, curves back across Arunachal Pradesh and Assam, then turns south to join the Padma and Ganga in Bangladesh and finally enters the Bay of Bengal. It is known by different names in different regions: as it flows through Tibet it is known as the Tsangpo., In the north-eastern states of Arunachal Pradesh and Assam, it is known as the Siang or Dihang. It is longer and more voluminous than the Ganga, and gushes down with enormous force for most of its course through the mountain regions and the forests of north-east India. A unique feature of this river is that it is navigable even at a height of 10 000 feet. When compared to the other major rivers in India, the Brahmaputra is less polluted but it has its own problems: petroleum refining units contribute most of the industrial pollution load into the basin along with other medium and small industries. The main problem facing the river basin is that of constant flooding. Floods have been occurring more often in recent years with deforestation, and other human activities being the major causes.

• Indus

  Known as the Sindhu in ancient times, the Indus was the cradle of India's great Indus Valley civilization. It has its source near Manasarovar close to southwestern Tibet, at an altitude of 16,000 feet and flows westward, through the Himalayas into Ladakh, and then through Sind and Punjab in Pakistan into the Arabian Sea. After flowing eleven miles beyond Leh, the Indus is joined by its first tributary, the Zanskar. When it enters the plains, its famous five tributaries - the Jhelum, Chenab, Ravi, Beas, and Sutlej - that give Punjab its name (land of the five rivers) join it. The name India is said to have its roots in Sindhu (Indus), the great river that constitutes the most imposing feature of that part of the subcontinent, home to some of the earliest civilizations.The river Sindhu has been invoked numerous times in the Vedic literature together with those of other gods and goddesses.

• Narmada

  This is the largest west-flowing river in India and originates from the Mekhala range in Shahdol district, Madhya Pradesh. It flows 1300 km west through the states of Madhya Pradesh and Gujarat before draining into the Gulf of Khambhat in the Arabian Sea. It is said to be one of the most beautiful rivers in India. In terms of its catchment area it is the seventh largest among the fourteen major river basins in the country. It is stated in the Matsya Purana that the mere sight of the river washes away all sins. With many short tributaries flowing into it from north and south, the Narmada basin forms a very important topographic feature of peninsular India. About 20% of the population along the river lives in the urban areas and the rest in the rural areas: Jabalpur, Hoshangabad, and Khargone in Madhya Pradesh, and Bharuch in Gujarat are some important cities located on the banks. The major cause of pollution is run-off from agricultural activities yet the pollution level is estimated to be lower than in other major rivers.

• Mahanadi

  This river is considered the lifeline of Orissa, through which it flows. It originates in south-eastern Madhya Pradesh near Raipur. In the upper drainage basin of the Mahanadi, which is centred on the Chhattisgarh Plain, periodic droughts contrast with the situation in the delta region where floods may damage the crops in what is known as the rice bowl of Orissa. The Hirakud Dam, constructed in the middle reaches of the Mahanadi, has helped in alleviating these adverse effects by creating a reservoir.

• Godavari

  This river originates in the Sahyadri range to the northeast of Mumbai in Maharashtra. It flows through that state and Andhra Pradesh before entering the Bay of Bengal. Its drainage basin is one of the largest in the country, second in size only to that of the Ganga; its delta on the east coast is also one of the country's main rice-growing areas. Despite the large catchment area the water available is only moderate because of the medium levels of annual rainfall.

• Kaveri

  The Kaveri is worshipped as a jeeva-nadi or perennial river. It has its origin in Talakaveri in the Kanara district of Karnataka and flows sounthwards through Tamil Nadu and Karnataka. The waters of the river have been a source of irrigation since antiquity; in the early 1990s, an estimated 95 percent of the Kaveri was diverted for agricultural use before it emptyied into the Bay of Bengal.
• Ground Water

Ground Water

The importance of groundwater for the existence of human society cannot be overemphasized. Groundwater is the major source of drinking water in both urban and rural India. Besides, it is an important source of water for the agricultural and the industrial sector. Water utilization projections for 2000 put the groundwater usage at about 50%. Being an important and integral part of the hydrological cycle, its availability depends on the rainfall and recharge conditions. Till recently it had been considered a dependable source of uncontaminated water.

The demand for water has increased over the years and this has led to water scarcity in many parts of the world. The situation is aggravated by the problem of water pollution or contamination. India is heading towards a freshwater crisis mainly due to improper management of water resources and environmental degradation, which has lead to a lack of access to safe water supply to millions of people. This freshwater crisis is already evident in many parts of India, varying in scale and intensity depending mainly on the time of the year.

Groundwater crisis is not the result of natural factors; it has been caused by human actions. During the past two decades, the water level in several parts of the country has been falling rapidly due to an increase in extraction. The number of wells drilled for irrigation of both food and cash crops have rapidly and indiscriminately increased. India's rapidly rising population and changing lifestyles has also increased the domestic need for water. The water requirement for the industry also shows an overall increase. Intense competition among users — agriculture, industry, and domestic sectors — is driving the groundwater table lower. The quality of groundwater is getting severely affected because of the widespread pollution of surface water. Besides, discharge of untreated waste water through bores and leachate from unscientific disposal of solid wastes also contaminates groundwater, thereby reducing the quality of fresh water resources.

Nadu, Uttar Pradesh, Karnataka, Madhya Pradesh, Maharastra, Bihar, and Delhi. Nearly half million people in India suffer from ailments due to excess of fluoride in drinking water. In some districts of Assam and Orissa, groundwater has high iron content. About 31% of the total area of Rajasthan comes under saline groundwater. Groundwater is saline in almost all of the Bhakra Canal in Punjab and the lift canal system in south-western Haryana. Similarly high levels of arsenic in groundwater have been reported in the shallow aquifers in some districts of West Bengal. Certain places in Haryana, Gujarat, and Andhra Pradesh were also found to have dangerously high levels of mercury. Causes of groundwater depletion and contamination Groundwater is an integral part of the environment, and hence cannot be looked upon in isolation. There has been a lack of adequate attention to water conservation, efficiency in water use, water re-use, groundwater recharge, and ecosystem sustainability. An uncontrolled use of the borewell technology has led to the extraction of groundwater at such a high rate that often recharge is not sufficient. The causes of low water availability in many regions are also directly linked to the reducing forest cover and soil degradation.

Pollution of groundwater resources has become a major problem today. The pollution of air, water, and land has an affect on the pollution and contamination of groundwater. The solid, liquid, and the gaseous waste that is generated, if not treated properly, results in pollution of the environment; this affects groundwater too due to the hydraulic connectivity in the hydrological cycle. For example, when the air is polluted, rainfall will settle many pollutants on the ground, which can then seep into and contaminate the groundwater resources. Water extraction without proper recharge and leaching of pollutants from pesticides and fertilizers into the aquifers has polluted groundwater supplies. In addition, leachates from agriculture, industrial waste, and the municipal solid waste have also polluted surface- and ground-water. Some 45 million people the world over are affected by water pollution marked by excess fluoride, arsenic, iron, or the ingress of salt water.

What can and should be done

It is important to realize that groundwater is not a resource that could be utilized unmindfully simply because it is available in abundant quantities. Problems and issues such as water logging, salinity, agricultural toxins, and industrial effluents, all need to be properly looked into. Other than legislation and checks to conserve and improve the quality of groundwater, society itself plays a very important role. During the last decade there has been a rising awareness among the common people on the need for conservation and development of groundwater. Water use has to be integrated effectively with water regeneration, as was done in many traditional technologies.

Renovation of forest tanks in drought-prone regions will have a significant impact on wildlife and forest cover. Similarly, in some urban cities there is a need to regenerate groundwater aquifers because of the high degree of dependence on them for drinking water. Rainwater harvesting schemes have been taken up in many cities and even made compulsory in some of them. Temple tanks need to be renovated and urban wetlands protected. All these will contribute to a rise in the groundwater level and a reduction of salt water ingress. Community awareness and management of freshwater resources should be enhanced. The government should implement effective groundwater legislation and regulations through self-regulation by communities and local institutions. External support agencies should support freshwater resource management. Environmental restoration should be promoted along with household water security. No single action whether community based, legislation, traditional water harvesting systems, or reliance on market forces will in itself alleviate the crisis in India. The effective answer to the freshwater crisis is to integrate conservation and development activities – from water extraction to water management – at the local level; making communities aware and involving them fully is therefore critical for success. All this will ultimately pave the way for combining conservation of the environment with the basic needs of people. In India, the Water (Prevention and Control) Act was passed by the Parliament in 1974, and by 1990 all the states adopted the act. In 1986, the Environment Protection Act was passed by the Parliament. Under both these acts, the states and the central government developed environmental norms for air emissions and waste water discharge for different types of sources.

• Glaciers

Glaciers

Glaciers are large sheets of ice that flow down very high mountains and are often the source of snow-fed rivers. Glaciers, found mainly in places such as Antarctica and Greenland, cover almost 10% of the earth's landmass, varying in size. A glacier begins life as snowflakes. As more snow falls and gathers, the weight of the snow on top compresses the lower layers to form ice. The pile of snow and ice becomes thicker and heavier till the point when the layer of ice at the very bottom melts under the pressure. It re-freezes almost at once; but the process is repeated over and over, and as a result the entire mass begins to slide downhill slowly along the rock surface. A glacier has an enormous impact on the topography of the area, pushing aside boulders, cutting through rocks, and denting its path as it moves.

Most of the world's glaciers are found at the Poles, but they exist on all of the world's continents, even Africa. Australia doesn't have any glaciers; however, it is considered part of Oceania, which includes several Pacific island chains and the large islands of Papua New Guinea and New Zealand. Both of these islands have glaciers. Glaciers require very specific geographical and climatic conditions. Most are found in regions of high snowfall in winter and cool temperatures in summer. The amount of precipitation (whether in the form of snowfall, freezing rain, avalanches, or wind-drifted snow) is important to glacier survival. In areas such as Siberia and parts of Antarctica, the lack of adequate precipitation prevents glacier development.

Some facts

• At presently, about 10% of the world's land area is covered with glaciers.
• Glaciers store about 75% of the world's freshwater.
• Glacierized areas cover over 15,000,000 square kilometres.
• In the United States, glaciers cover over 75,000 square kilometres, with most of the glaciers located in Alaska.
• During the last Ice Age, glaciers covered 32% of the total land area.
• If all land ice melted, the sea level would rise approximately 70 metres worldwide.
• North America's longest glacier is the Bering Glacier in Alaska, measuring 204 kilometres long.
• The Malaspina Glacier in Alaska is the world's largest piedmont glacier, covering over 8,000 square kilometres and measuring over 193 kilometers across at its widest point. In India, glaciers are found in the Himalayas. There are about 15,000 glaciers flowing through these mountains, covering about 17% of the mountain area and supporting numerous perennial rivers such as the Ganga, Indus, and Brahmaputra. Some well-known glaciers are described below.

Dokriyani

This glacier is believed to be as old as the Himalayan Mountains. Dokriani 'Bamak' is a well-developed medium sized glacier of the Bhagirathi basin. The glacier is 5 km long and flows in a northwest direction terminating at an elevation of 3,800 m. It originates at an altitude of 13 000 feet in Uttaranchal's Garhwal district. It is one of the most studied glaciers in the world. A recent study says that it has been shrinking by a few metres every year.

Gangotri

This is located in Uttaranchal's Tehri Garhwal. One of the oldest glaciers in the Chaukhamba range, it is where the river Ganga originates. The Gangotri is not a single valley glacier, but a combination of several other glaciers that are fed to it and form a huge mass of ice. The glacier covers 28km and terminates at Gaumukh (4,000m).

Pindari

This is one of the most beautiful glaciers in the Kumaon hills and is known as the Jewel of Kumaon. iIt is located at a height of 13 000 feet above sea level between the Nanda Devi and Nandakot peaks and terminates at an altitude of 3,627 m. It is 5 km long, the snout is about 6 m high and 2.5 m wide and above the snout, the glacier extends for about 3m. The Pinder River that emerges from the Pindari glacier drains the valley.

Zemu

The Zemu glacier is the largest and most famous glacier in the eastern Himalayas, with a length of about 26 km. It is located in northwestern Sikkim in a U-shaped valley at the base of the Kanchenjunga massif. The Teesta river has its source in this glacier. Many tributary glaciers feed the trunk glacier.

Siachen

This is the largest glacier in the world outside the Polar regions, stretching over a length of about 72 km. It lies in the extreme north- central part of Jammu and Kashmir near the border of India and Tibet, on the north-facing slopes of the Karakoram Range, and feeds the Shaksgam river that flows into Tibet. The glacier can be approached from Skardu in Ladakh. To the east of the Siachen lies a group of three glaciers known as the Rimo North, Central, and South. Between them, these glaciers have almost 700 square km of ice, which, at places, is 100 m deep. Altogether, the glaciers contain about 200 cubic kilometres of ice.

• Lakes

Lakes

A lake is a low-lying part of the Earth's surface in which rainwater, surface water run-off, outflow from a river, and water from other sources accumulates. There is a great variety of lakes on Earth: there are freshwater lakes and saltwater lakes, ranging in size from small fish-ponds to huge waterbodies such as Lake Superior in USA which is the world's largest freshwater lake. The Caspian Sea in Europe and the Sambhar lake in Rajasthan are examples of saltwater lakes. India has a large number of lakes spread all over the country, from Kashmir to Kerala and from Rajasthan to Assam. Among the better-known fresh water lakes in India are the Dal lake in Srinagar and the Nainital lake. Whether natural or manmade, all lakes are major sources of water. Lakes are homes to a large variety of aquatic life, with one notable exception: the Dead Sea, a saltwater lake in Israel does not have any form of life. There is too much salt in its water to sustain life.

Almost half of the world's lakes are degraded, depleted, and contaminated mainly by human activities. The main causes are inflow of domestic sewage, agricultural run-off, discharge of industrial effluents, over-fishing, introduction of exotic species and habitat degradation from population growth, expansion of cities. As more water is withdrawn for human use and more of it is returned to lakes and rivers badly polluted there is less available to maintain vital freshwater ecosystems

Some India Lakes

Keoladeo National Park

This is an important habitat for waterfowl. It is the only wintering site in India for the central and western Asian population of Siberian cranes, a highly endangered species. The population of Siberian Cranes has decreased in the last two decades. In a programme now underway, reared Siberian crane chicks are being brought to Keoladeo from USA and Siberia. Loktak Lake. The measures undertaken for the conservation of Loktak Lake so far, include afforestation of indigenous species including fruit trees; control of silt; catchment area treatment; removal of floating lands locally called phumdis in some pockets of the lake; and generating awareness about the values and functions of the wetland. Several measures have been adopted to control the prolific growth of phumdis and water hyacinth. Weevils have been introduced for biological control of water hyacinth.

Wular Lake

This wetland is the source of drinking water for Srinagar, and also acts as an absorption basin for floodwater. It is an important waterfowl habitat. However, Wular Lake is subject to heavy siltation due to loss of vegetal cover in the surrounding area.

Sambhar Lake

Located in the arid zone of Rajasthan, the Sambhar Lake is one of the largest inland saline lakes in India. This wetland is one of the most important wintering areas for flamingoes and pelicans. Salt extraction is one of the major activities in the wetland.

The Bhoj Wetland in Bhopal, Madhya Pradesh

It consists of two man-made lakes (upper and lower lakes). The upper lake was created in the 11th century by constructing an earthen dam across the Kolans river and the lower lake was constructed nearly two centuries ago. The wetland supports a wide variety of flora and fauna. Diverse flora provide ideal habitat for a large number of avifauna. Biotic interaction and natural selection have led to the development of a characteristic relationship between vegetation and the avifauna.

Deepor Beel

This is a permanent freshwater lake, in a former channel of the Brahmaputra river, south-west of Guwahati city. It is a large natural wetland having great biological and environmental importance and is also the only major storm water storage basin for Guwahati. The beel is endowed with rich floral and faunal diversity. In addition to a huge congregation of residential water birds, the Deepor ecosystem harbours a large number of migratory waterfowl each year. It is now threatened with large scale encroachment, brick making factory and soil cutting within the beel ecosystem, and construction of railway line along the southern boundary of the beel.

The Hussain Sagar Lake

This is one of the largest man-made lakes in Asia, located in the heart of Hyderabad, contributing to its immense beauty. It is a sprawling artificial lake that holds water perennially. It was built during the reign of Ibrahim Qutub Shah in 1562, on a tributary of the river Musi.

The Tso Morari Lake

This is one of the largest in the Ladakh region and is almost like an inland sea. Situated at an elevation of about 4,900m, it is about 22km long, with a width varying from 5 to 7km and a depth of more than 30 m at the deepest point. The lake is probably a leftover from the Ice Age, formed by the melt waters of the ice masses left behind by the retreating glaciers. The waters from the surrounding areas drained into the lake. The huge amounts of water present in the beginning evaporated very fast in the desert-like atmosphere and what was fresh water became brackish and finally salty, unfit for human consumption.

One of the most spectacular lakes in Ladakh is the Pangong Tso, which lies across the Changla Pass from Leh. At an altitude of almost 4,500 metres, the Pangong Tso is only 8 km wide at its broadest point, but is an amazing 134km long. The Pangong is considered to be the longest lake in Ladakh. It is a saltwater lake formed in much the same way as the Tso Morari lake during the Ice Age.

3) Water Pollution

• Oil Spills

Oil Spills

Among the most dangerous of all water pollutants is fuel oil. Oil spills from tankers at sea or leaks from underground storage tanks on land are very difficult to control as oil tends to spread very fast, affecting a large area in a very short time. They are a major menace to the environment as they cause severe damage to surrounding ecosystems. Oil spills at sea decrease the oxygen level in the water and cause grave harm to the creatures living in the sea. Since crude oil is lighter than water, it floats on the surface and poses the threat of swift-spreading fire. Oil spills are rather common as oil tankers can meet with accidents either in deep sea or offshore, while waiting to be loaded or unloaded. During the Gulf War, several oil reservoirs were destroyed at sea and the effect on marine life was devastating. Seabirds and fish were washed ashore, their bodies covered with oil. On land crude is transported through pipelines or tankers which can get damaged and spew out crude oil over the land, thereby contaminating it. Bioremediation is a method that is now being use to put a check to the damage done by this oil spill.

• Health Impact

HEALTH IMPACTS OF WATER POLLUTION

It is a well-known fact that clean water is absolutely essential for healthy living. Adequate supply of fresh and clean drinking water is a basic need for all human beings on the earth, yet it has been observed that millions of people worldwide are deprived of this.

Freshwater resources all over the world are threatened not only by over exploitation and poor management but also by ecological degradation. The main source of freshwater pollution can be attributed to discharge of untreated waste, dumping of industrial effluent, and run-off from agricultural fields. Industrial growth, urbanization and the increasing use of synthetic organic substances have serious and adverse impacts on freshwater bodies. It is a generally accepted fact that the developed countries suffer from problems of chemical discharge into the water sources mainly groundwater, while developing countries face problems of agricultural run-off in water sources. Polluted water like chemicals in drinking water causes problem to health and leads to water-borne diseases which can be prevented by taking measures can be taken even at the household level.

Groundwater and its contamination

Many areas of groundwater and surface water are now contaminated with heavy metals, POPs (persistent organic pollutants), and nutrients that have an adverse affect on health. Water-borne diseases and water-caused health problems are mostly due to inadequate and incompetent management of water resources. Safe water for all can only be assured when access, sustainability, and equity can be guaranteed. Access can be defined as the number of people who are guaranteed safe drinking water and sufficient quantities of it. There has to be an effort to sustain it, and there has to be a fair and equal distribution of water to all segments of the society. Urban areas generally have a higher coverage of safe water than the rural areas. Even within an area there is variation: areas that can pay for the services have access to safe water whereas areas that cannot pay for the services have to make do with water from hand pumps and other sources.

In the urban areas water gets contaminated in many different ways, some of the most common reasons being leaky water pipe joints in areas where the water pipe and sewage line pass close together. Sometimes the water gets polluted at source due to various reasons and mainly due to inflow of sewage into the source. Ground water can be contaminated through various sources and some of these are mentioned below.

Pesticides. Run-off from farms, backyards, and golf courses contain pesticides such as DDT that in turn contaminate the water. Leechate from landfill sites is another major contaminating source. Its effects on the ecosystems and health are endocrine and reproductive damage in wildlife. Groundwater is susceptible to contamination, as pesticides are mobile in the soil. It is a matter of concern as these chemicals are persistent in the soil and water.

Sewage. Untreated or inadequately treated municipal sewage is a major source of groundwater and surface water pollution in the developing countries. The organic material that is discharged with municipal waste into the watercourses uses substantial oxygen for biological degradation thereby upsetting the ecological balance of rivers and lakes. Sewage also carries microbial pathogens that are the cause of the spread of disease.

Nutrients. Domestic waste water, agricultural run-off, and industrial effluents contain phosphorus and nitrogen, fertilizer run-off, manure from livestock operations, which increase the level of nutrients in water bodies and can cause eutrophication in the lakes and rivers and continue on to the coastal areas. The nitrates come mainly from the fertilizer that is added to the fields. Excessive use of fertilizers cause nitrate contamination of groundwater, with the result that nitrate levels in drinking water is far above the safety levels recommended. Good agricultural practices can help in reducing the amount of nitrates in the soil and thereby lower its content in the water. Synthetic organics. Many of the 100 000 synthetic compounds in use today are found in the aquatic environment and accumulate in the food chain. POPs or Persistent organic pollutants, represent the most harmful element for the ecosystem and for human health, for example, industrial chemicals and agricultural pesticides. These chemicals can accumulate in fish and cause serious damage to human health. Where pesticides are used on a large-scale, groundwater gets contaminated and this leads to the chemical contamination of drinking water.

Chemicals in drinking water

Chemicals in water can be both naturally occurring or introduced by human interference and can have serious health effects.

Fluoride. Fluoride in the water is essential for protection against dental caries and weakening of the bones, but higher levels can have an adverse effect on health. In India, high fluoride content is found naturally in the waters in Rajasthan. Arsenic. Arsenic occurs naturally or is possibly aggrevated by over powering aquifers and by phosphorus from fertilizers. High concentrations of arsenic in water can have an adverse effect on health. A few years back, high concentrations of this element was found in drinking water in six districts in West Bengal. A majority of people in the area was found suffering from arsenic skin lesions. It was felt that arsenic contamination in the groundwater was due to natural causes. The government is trying to provide an alternative drinking water source and a method through which the arsenic content from water can be removed.

Lead. Pipes, fittings, solder, and the service connections of some household plumbing systems contain lead that contaminates the drinking water source. Recreational use of water. Untreated sewage, industrial effluents, and agricultural waste are often discharged into the water bodies such as the lakes, coastal areas and rivers endangering their use for recreational purposes such as swimming and canoeing. Petrochemicals. Petrochemicals contaminate the groundwater from underground petroleum storage tanks.

Other heavy metals. These contaminants come from mining waste and tailings, landfills, or hazardous waste dumps.

Chlorinated solvents. Metal and plastic effluents, fabric cleaning, electronic and aircraft manufacturing are often discharged and contaminate groundwater.

Disease

Water-borne diseases are infectious diseases spread primarily through contaminated water. Though these diseases are spread either directly or through flies or filth, water is the chief medium for spread of these diseases and hence they are termed as water-borne diseases.

Cause	Water-borne diseases
Bacterial infections	Typhoid Cholera Paratyphoid fever Bacillary dysentery
Viral infections	Infectious Hepatitis (jaundice) Poliomyelitis
Protozoal infections	Amoebic dysentery

Most intestinal (enteric) diseases are infectious and are transmitted through faecal waste. Pathogens – which include virus, bacteria, protozoa, and parasitic worms – are disease-producing agents found in the faeces of infected persons. These diseases are more prevalent in areas with poor sanitary conditions. These pathogens travel through water sources and interfuses directly through persons handling food and water. Since these diseases are highly infectious, extreme care and hygiene should be maintained by people looking after an infected patient. Hepatitis, cholera, dysentery, and typhoid are the more common water-borne diseases that affect large populations in the tropical regions. A large number of chemicals that either exist naturally in the land or are added due to human activity dissolve in the water, thereby contaminating it and leading to various diseases.

Pesticides. The organophosphates and the carbonates present in pesticides affect and damage the nervous system and can cause cancer. Some of the pesticides contain carcinogens that exceed recommended levels. They contain chlorides that cause reproductive and endocrinal damage.

Lead. Lead is hazardous to health as it accumulates in the body and affects the central nervous system. Children and pregnant women are most at risk. Fluoride. Excess fluorides can cause yellowing of the teeth and damage to the spinal cord and other crippling diseases.

Nitrates. Drinking water that gets contaminated with nitrates can prove fatal especially to infants that drink formula milk as it restricts the amount of oxygen that reaches the brain causing the ‘blue baby’ syndrome. It is also linked to digestive tract cancers. It causes algae to bloom resulting in eutrophication in surface water. Petrochemicals. Benzene and other petrochemicals can cause cancer even at low exposure levels.

Chlorinated solvents. These are linked to reproduction disorders and to some cancers. Arsenic. Arsenic poisoning through water can cause liver and nervous system damage, vascular diseases and also skin cancer.

Other heavy metals. –Heavy metals cause damage to the nervous system and the kidney, and other metabolic disruptions.

Salts. It makes the fresh water unusable for drinking and irrigation purposes. Exposure to polluted water can cause diarrhea, skin irritation, respiratory problems, and other diseases, depending on the pollutant that is in the water body. Stagnant water and other untreated water provide a habitat for the mosquito and a host of other parasites and insects that cause a large number of diseases especially in the tropical regions. Among these, malaria is undoubtedly the most widely distributed and causes most damage to human health.

Preventive measures

Water-borne epidemics and health hazards in the aquatic environment are mainly due to improper management of water resources. Proper management of water resources has become the need of the hour as this would ultimately lead to a cleaner and healthier environment.

In order to prevent the spread of water-borne infectious diseases, people should take adequate precautions. The city water supply should be properly checked and necessary steps taken to disinfect it. Water pipes should be regularly checked for leaks and cracks. At home, the water should be boiled, filtered, or other methods and necessary steps taken to ensure that it is free from infection.

Minamata: environmental contamination with methyl mercury

In Minamata, Japan, inorganic mercury was used in the industrial production of acetaldehyde. It was discharged into the nearby bay as waste water and was ingested by organisms in the bottom sediments. Fish and other creatures in the sea were soon contaminated and eventually residents of this area who consumed the fish suffered from MeHg (methyl mercury) intoxication, later known as the Minamata disease. The disease was first detected in 1956 but the mercury emissions continued until 1968. But even after the emission of mercury stopped, the bottom sediment of the polluted water contained high levels of this mercury.

Various measures were taken to deal with this disease. Environmental pollution control, which included cessation of the mercury process; industrial effluent control, environmental restoration of the bay; and restrictions on the intake of fish from the bay. This apart research and investigative activities were promoted assiduously, and compensation and help was offered by the Japanese Government to all those affected by the disease.

The Minamata disease proved a turning point, towards progress in environment protection measures. This experience clearly showed that health and environment considerations must be integrated into the process of economic and industrial development from an early stage.

• Corals

CORALS

Corals are small, sedentary marine animals that occur in dense colonies in warm shallow waters of oceans. Reef-building corals are scattered throughout the tropical and subtropical western Atlantic and Indo-Pacific oceans, generally between 30 degrees North and 30 degrees South latitudes. Coral reefs are formed by the skeleton remains of many generations of stony corals. Massive reef structures are built over thousands of years by tiny coral polyps aided by minute algae (zooxanthellae) that live in their tissues, calcifying algae, and other organisms that secrete calcium carbonate and adhesives. Reef- building corals are generally found at depths of less than 46 m, where there is sunlight and clear water through which the sunlight penetrates better. Reef-building corals, along with the algae, require warm ocean temperatures (20–28° C) and are therefore found along the eastern shores of major land masses where the water is warmer. These reefs are amongst the earth’s oldest living communities of plants and animals. They vary in shape, size and colour.

Coral ecosystem

Coral reefs are sometimes referred to as ‘tropical rainforests of the deep’ since they are one of the most diverse, productive, and beautiful marine ecosystems in the world. The extraordinary diversity of reefs makes them biologically important and, like rainforests, they have provided valuable scientific insights into the nature of underwater ecology. It is a diverse collection of species that interact with each other and the physical environment. The sun is the initial source of energy for this ecosystem. They are considered to be one of the most sensitive to any change. When they are environmentally stressed they lose much of the algae that give them the colour along with other pigments. When this happens the corals appear white in colour and are referred to as bleached.

Excessive growth and accumulation of phytoplankton and seaweed would be detrimental to coral vitality and diversity, and low nutrient conditions are needed to prevent this. Diverse and abundant populations of grazing fish and invertebrates also keep the growth down.

Creatures found on coral reefs

The coral reef ecosystem is a diverse collection of species that interact with each other and the physical environment. The numerous species residing and depending on coral reefs represent a bank containing the genetic diversity necessary for adaptation to changes in the environment. Sponges have been an important part of the coral reef ecosystem. Sea anemones provide shelter to the fish and other creatures in the reefs. Fishes play a vital role in the reef's food web, acting as both predators and prey. Bryozoans are microscopic invertebrates that form branching colonies over coral skeletons and reef debris, cementing the reef structure.

The reef is also home to a variety of worms, shrimps, crabs, lobsters, starfish, sea cucumbers, and sea urchins. Octopuses, squids, clams, scallops, marine snails, and also some species of sharks, skates, and rays live on or near the reef. Some sea turtles frequent reef areas. Green, loggerhead, and hawksbill sea turtles live in the warm waters of the Great Barrier Reef.

The predators

The crown of thorns, a starfish, is a well- known predator of coral. Large numbers of these starfish can devastate reefs, leaving behind only the calcium carbonate skeletons. Parrotfish use chisel-like teeth to nibble on hard corals and eat the algae within the coral. Eels are one of the reef's largest predators and feed on the small fishes, octopuses, shrimps, and crabs.

Types of reefs

There are three types of reefs: the fringing reef, the barrier reef, and the atoll.

• Fringing reefs border shorelines of continents and islands in tropical seas.
• Barrier reefs occur farther offshore. The Great Barrier Reef off northern Australia in the Indo-Pacific is the largest barrier reef in the world. This reef stretches more than 2000 km.
• Atolls are reefs that surround a central lagoon. The result is several low coral islands around a lagoon. Atolls commonly occur in the Indo-Pacific region.

Importance of corals and coral reefs

• Corals remove and recycle carbon dioxide. Excessive amounts of this gas contribute to global warming.
• Reefs shelter land from harsh ocean storms and floods by breaking the force of the waves, thereby allowing mangroves and sea grass to flourish.
• Reefs provide resources for fisheries.
• They attract millions of tourists every year.
• The coral reef is an intricate ecosystem and contains a diverse collection of organisms. Without the reef, these organisms would die.
• Coral skeletons are being used as bone substitutes in reconstructive bone surgery.
• The coral reef provides a living laboratory for both students and scientists.

Major threats to coral reefs

Deforestation, construction, and other activities have led to silt or sand covering the corals, smothering them, and preventing light from passing through.

Mangroves and sea grass that normally act as filters for sediment are being rapidly destroyed.

Prawn harvesters have destroyed large areas of corals to create artificial prawn farms.

Fishing with explosives have reduced nearby coral to lifeless rubble.

• Over fishing makes this problem even worse because the fish that would normally eat the algae have been captured and killed.
• Commercial fishing fleets often use cyanide and other poisons to stun and capture valuable reef fish. This poisons not only the fish but the coral polyps and other creatures in the area as well. In the Philippines, less than 10% of the coral reefs remain healthy due to extensive fishing.
• Trash dumped into the water can also kill coral reef life.
• Fertilizers and sewage dumped into coastal waters encourage rapid algae growth which chokes coral polyps, cutting off their supply of light and oxygen. This appears to be the case in some parts of the Great Barrier Reef.
• Careless boating, diving, fishing, and other recreational uses of coral reef areas can cause damage to coral reefs.
• Coral reefs are also threatened by global warming. There has been an unprecedented increase in the number of coral bleaching events during the past 2 decades (which have had some of the warmest years in history). When ocean temperatures get too high, coral lose the symbiotic algae inside them, causing them to turn white, or ‘bleach’, and eventually die.

While coral reefs are sensitive to environmental changes, they appear to be able to recover effectively from physical disturbance or temporary pollution events provided the water quality is generally high. For example, the corals in Kaneohe Bay, Hawaii, for the most part recovered from severe overgrowth of algae after sewage inputs were diverted away from the Bay.

Conservation measures

The world has woken up to the magnitude of the problem and has taken steps to halt this degradation of one of the richest eco systems. The Convention on International Trade in Endangered Species of Wild Fauna and Flora, or CITES, has classified many corals as threatened species. The establishment of marine sanctuaries or preserves may help ensure the availability of this ecosystem in the years to come. The Great Barrier Reef Marine Park was established in 1975 and is the largest project undertaken to preserve the coral reef in the world. Initiatives for the preservation of coral reefs in India have been undertaken on a large scale in the Wandur Marine National Park in the Andaman Nicobar islands. People on their part can play a role in preventing this depletion. Corals should not be collected, either alive or dead. All waste should be treated before it is released into the sea and no waste is to be dumped directly into the water. Once this awareness is built in the people the well being of these reefs can be ensured