INTRODUCTION:

Earth is the only planet in the solar system where life exists. Several conditions of this planet help it to retain life. One among them is the presence of water. The mass and size of earth are quite large enough to retain water. Water is the most important need of all living things.

Water is useful to humans for generation of hydroelectric power, irrigation, industry, household purposes, fish culture, recreation, dilution of harmful pollutants and other purposes. Although, 75% of earth's surface is covered by water only a small portion of it (about 0.5%) is soft water (i.e., the drinking water).

Lakes, rivers, wetlands and watershed areas are some of the reservoirs of useful drinking water on land. Many processes maintain the ecosystem and quality of water in lakes. Some of them are: nutrient retention by riparian forests, foodweb structures which provide nutrients to phytoplanktons and other primary producers, and biogeochemical cycles help to restore vital substances in lakes.

CHARACTERISTICS OF LAKES:

1. Resilience: This system is the one, which helps to maintain a certain environment when it is subjected to disturbance or in other words, it is the capability of an environment to retain its original position when it is disturbed. Lakes are disturbed in many ways. It can be either by the input of solar radiation or by extreme changes in climatic condition or even due to changes in riparian vegetation (vegetation that grows on the banks of lakes and rivers). But their retention rates depend on the intensity of disturbance.
The physico-chemical and biological characteristics of lake water depend on several factors including location of water body, type of sewage and domestic waste disposal, localized human population in surroundings and their activities. As a result, large quantity of organic and inorganic nutrients is added.

2. Return time: It is related to nutrient turn over rate in lakes. eg. nitrogen, phosphorus, carbon and such other nutrients consumed by producer, in the food chain are returned to same environment by decomposers.

From this table it can be noticed that phosphorus enrichment (eutrophication) in the lakes reduced the return rate in that specific lake.

CURRENT STATUS OF LAKES:

Due to indiscriminate meddling of man, lakes are on the verge of extinction. Harmful activities of man have resulted in degradation of lakes. Agricultural wastes, sewage and drainage water from urban areas, absence of wetlands and riparian vegetation near the lakes, etc., are some of the causes that lead to degradation of lakes. Sometimes recreational activities of man also lead to degradation. For eg. weeds are throttling the famous Dal and Nagin lakes of Srinagar. The culprits are the hordes of tourists who throw the leftovers of meals into the lakes. Weeds feed on these and multiply, choking the lakes to death. Many other activities of man also lead to degradation of lakes.

WHAT IS EUTROPHICATION? HOW DOES IT AFFECT A LAKE?

Eutrophication is the main cause of lake degradation. High nitrate and phosphate content in water leading to extreme growth of producers, causing degradation of water resources is referred to as eutrophication.

Enrichment of nutrients also occurs due to disposal of domestic and industrial effluents from surrounding areas, which support the growth of a variety of macrophytes and microbes. It is caused due to phosphorus runoff from agricultural lands and urban areas. Eutrophication is also caused due to the loss of wetlands and riparian vegetation.

Nowadays, farmers use more and more fertilizers for better yields. Farms import phosphorus, in the form of animal feeds to grow livestock and as fertilizers to grow crops. But the excess phosphorus is eroded and is brought to lakes. Thus underdevelopment near wetlands and lack of riparian vegetation also contribute to eutrophication. Sewage and drainage waters find their way to rivers and lakes. Like decomposed manure they too help in building up the concentration of phosphorous at an alarming rate.

As such, humic inputs decrease, but at the same time phosphorus inputs increase leading to abundance of phytoplanktons, planktivorous fishes and bottom feeding fishes. But piscivorous fishes (fishes that feed on smaller fishes) decrease due to intense fishing. This disturbs the food web. More and more incoming phosphorus gets accumulated in blue green algae resulting in dense algal blooms. So macrophytes decrease because of low water clarity and there is increase in bottom feeding fishes. From all these perturbations toxic pollutants begin to accumulate further. Old useful species are exterminated and new species make their appearance leading to total breakdown in food web structures, degrading the lakes and leading to loss of a habitat. Transparency of water will be destroyed by eutrophication and the lake water becomes turbid.

WET LANDS AND RIPARIAN VEGETATION (AND THEIR DEPLETION):

Wet lands act as water storing systems that delay the water from reaching the lakes and thus prevent them from floods. They also provide nutrients and humic substances to the lake.

Vegetation, which grows near the rivers and the lakes, is known as riparian vegetation. They are a source of fallen trees that provide food mainly for consumers in lakes. In fact, riparian vegetation prevents the collection of silt. Depletion of these valuable resources will result in the eutrophication of lakes.

Organochlorine chemicals (eg. DDT) are harmful to lakes and vegetation, the excess of which can wipe out the entire riparian vegetation. In the absence of riparian vegetation, toxic pollutants enter the lakes directly and may lead to death of aquatic organisms. They can also reduce the quality of wetlands.

Nowadays, due to extreme use of fossil fuels and firewood, oxides of sulphur are being released in to the atmosphere. They combine with atmospheric moisture to form acids. Rainwater dissolves them and brings them down to earth. Acid rains can deplete wetlands and riparian areas, affecting the lakes adversely.

One of the main problems faced by man in these days is ozone depletion. It is mainly due to CFC's (Chloroflurocarbons) which are used in refrigerators and air conditioners. Aerosol sprays also result in the depletion of ozone layer. The resultant problem is irradiation of UV rays, which are entering directly in to the earth in very high doses. As such, it may lead to mutations and other dangerous diseases. It causes adverse effects on aquatic organisms and the lake water becomes more transparent to UV rays resulting in the decline of humic production.

According to a survey, 2/3rd of all illnesses in India are related to water-borne diseases. These might also assume epidemic proportions.

Water pollution also has several adverse effects on aquatic biota. Occurrence of massive fish kills and destruction of lower aquatic life forms due to pollutants of various kinds have become a regular feature in various parts of the country. Granite operations near lakes and wetlands also degrade them.

ROLE OF INDUSTRIES IN WATER POLLUTION:

Even though industries are very essential for the development of a country, they are the main depletors of the environment. By-products formed during industrial processes are often passed into water resources, degrading them.

In the figure below, it can be noticed that waste chemicals, which are toxic, are being released to nearby water resources, which affect the life of organisms.

Mercury is a classic example of a water pollutant. It is a by-product of power-plants. It sometimes gets methylated (e.g. methyl mercury) and moves in food chains through bio-magnification. It can cause physical retardation in aquatic organisms. It can also degrade the water quality and clarity.

Nuclear power reactors discharge radioactive wastes and radionuclides in to lakes, rivers and seas. These toxic radioactive pollutants are more harmful to biota.

Superheated water from thermal power stations and nuclear reactors are often fed into waterbodies. It may have adverse affects on water resources and the organisms. It prevents humic production and the diffusion of oxygen in them. Thus, deposition of phosphorus increases rapidly leading to eutrophication.

RESTORATION OF LAKES AND WETLANDS:

Economically, degraded lakes are less valuable than the normal lakes and represent loss of economic benefits. As such, restoration of lakes would be of great use. The main point regarding this objective is efficient management. But the main problem is that the degraded state is resilient, which has to be overcome to restore the lakes. Effective remedial measures can restore the lakes to a considerable extent.

Manipulating the natural foodwebs using certain predominantly herbivorous fishes, will save the cost of other treatments for reclamation, and fishes capable of cleaning algal blooms can control eutrophication.

To prevent eutrophication, excessive use of fertilizers has to be controlled and sewage and industrial effluents should be suitably treated. Mixed cropping and rotation of crops can prevent excessive use of inorganic fertilizers.

Sewage treatment includes three steps:

Suspended materials are removed.

Wastewater is aerated to promote bacterial decomposition of organic compounds. This is followed by chlorination.

Nitrates and phosphates are removed and the water is purified. The nitrates and phosphates removed from the wastewater can be used as fertilizers in the farms and fields.

Toxic industrial effluents can be treated to eliminate the pollutants. The steps involved are:

In this treatment, metallic compounds and metals that are precipitated can be reused and recycled. Water so obtained from these treatments is used for various purposes (i.e., fulfilling human needs and services).

Use of organochlorine chemicals like DDT must be abandoned and natural materials should be used instead. It is very important to maintain the water quality. Neem can be an alternative for DDT. It increases the yield without affecting the fertility of the land.

In order to prevent acid precipitation, use of fossil fuels has to be controlled and alternate sources of energy can be used. Solar energy a freely available and pollution free form of energy can be an alternative. Likewise, electricity is also a pollution free energy that can be used as an alternative. Control of acid precipitation will restore the wetlands as well as the riparian vegetation.

Self-regulating feed back mechanisms would bring the metal polluted ecosystem back to a homeostatic state. Addition and deletion of metallic compounds can be readily equilibrated or compensated (metal ion homeostasis).

Apart from these, USA has launched W.R.P. (Wetlands Reserve Programme) in order to restore wetlands, thereby indirectly restoring the lakes. Its objectives include:

On similar lines, many organisations exist in India to prevent the degradation of lakes and to control water pollution. For eg. Central Ganga Authority has been established by the Government of India to prevent the pollution of the river Ganga that protect water shed vegetation and facilitates proper land use.

Water Act (Prevention and Control of pollution) promulgated and passed in parliament in 1974, could be an effective legal measure in the control of pollution provided concerned agencies implement it.

CONCLUSION:

Nowadays, lakes are degraded rapidly, but their restoration programmes are only a few. This is because polluters have not been penalised, and the general public and stakeholders have not been included in the decision making process and are not getting sufficient economic benefits from restoration. Restoration programmes are not the work of a single person, but the responsibility of whole mankind. Awareness generated among the people regarding the pollution of lakes will be more effective. People must also be aware of their duties and services in this direction.

As the proverb goes "Prevention is better than cure", it is much more efficient to avoid degradation of lakes than restoring their quality after their pollution. Prevention at the source appears to be more and more effective than the latter rectification of pollution. 'Development without destruction' can be of great use.

ADDRESS:

1.) Udaya English Medium High School,
Vijayanagar,
Bangalore - 40,
Karnataka,
India.