Water is one of the most important substances on the earth. Water generates the hydrosphere, circulates in the atmosphere, and infiltrates deep into the ground and moves through the lithosphere and sustains the biosphere. Fresh water source like lake is a renewable resource following the hydrological cycle, it is not evenly distributed on the earth’s surface. Lakes are large water bodies, which have an important impact on human emotions such as security, happiness and creative aspects of behavior. These are not mere decorative bodies but are biological and psychological necessities. Environmentally lakes are one of the important ecosystems. They play a significant role in recharge and maintenance of ground water table. They have a great recreational potential in the form of water sports, boating etc. in today’s fast and stressful life style. In case of emergency, they can serve as source of water for fire fighting etc. They can also be used for Aquaculture as a source of income. They add to the beauty of the city promoting tourism.
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The lakes and reservoirs, all over the country are facing degradation. The degradation is due to encroachments and eutrophication (from domestic and industrial effluents) and silt accumulation. There has been a considerable increase in urban population especially after industrial revolution. The human settlements have taken place in and around the ponds and lakes to mitigate their demands, resulting in contaminating the water sources. The need of Conservation and Management of Lakes is therefore rightly understood by the world community and the issues relating Conservation of lakes are on the anvil.
In Lentic or lake ecosystems, the aging process is just the reverse of lotic or river systems. Where as streams tend to get wider and deeper as they age, lakes tend to get shallower and the banks extend into what was originally open water. Natural filling is generally due to wind blown materials (soil, leaves, etc.) entering the system, sediment input by terrestrial run off, aquatic plant and animal debris and eutrophication.
When the balance is upset between photosynthesis and decomposition due to enrichment of water by inorganic plant nutrients, either too much organic material accumulates without getting decomposed adequately or too many bacteria are present and an overabundance of decomposition occurs, the lake is classed as Eutrophic. They are considered to be middle aged systems. They are relatively shallow in comparison to Oligotrophic lakes. They have a silty or mud bottom and have sufficient nutrients to support a large population of animals.
The accelerated or cultural eutrophication of several waterbodies is caused by human activity. Large quantities of mineral nutrients and organic matter are added to the waterbodies in the form of sewage effluents, organic wastes, agricultural run-offs, excreta and
The Process of Eutrophication
sewage (liquid domestic & Industrial waste)
minerals esp. nitrates
minerals esp. nitrates
competition for light
consumers canââ‚¬â„¢t consume fast enough
use up oxygen by aerobic respiration (increased BOD)
aerobes die invertebrates, fish etc.
anaerobic bacteria thrive, release NH4,CH4,H2S
exudates of animals and humans etc. These provide plenty of phosphates, nitrates (mostly of fertilizers applied to agricultural lands, domestic sewage etc.) which lead to exuberant growth of algae and other water plants. A rich microbial and animal population also develops. The process of natural Eutrophication which is generally very slow , thus gets accelerated. Silt and organic debris accumulates at the bottom and the system turns into a shallow muddy pond, then to a marsh and finally into a dry land. Thus a waterbody which could have been useful as a reservoir of fresh water and could have helped the growth of fish etc. for hundreds of years becomes totally useless within a span of few years only.
Sources of Lake Pollution:
The sources of Pollution can be classified as fixed point sources and Non-point Sources
EFFECTS OF EUTROPICATION
Undesirable effects of Eutrophication
The decaying algae, fish, planktons and other organisms cause foul smell.
On depletion of oxygen level and on exhausting nitrate oxygen, sulphates are reduced as a last resort to yield hydrogen sulphide which results in bad smell and putrefied taste of water.
The lakes become aesthetically unpleasant.
Plant growth and silt hinder recreation activities.
Rate of sedimentation increases, which shortens the life span of lakes.
Mosquito nuisance increases causing health hazards to nearby residents.
Steps to Control Eutrophication
Effective waster water treatment and removal of nutrients like nitrogen and phosphorous before discharging the sewerage into waterbodies.
Controlling the recycling of nutrients through harvest.
Effective disposal of organic matter as sludge.
Developing phosphate-free detergents for domestic use.
Adopting effective Physico-chemical methods for removal of dissolved nutrients such as nitrogen & phosphorous compounds.
Overcoming the temptation of over-fertilization.
Remedial Measures for Eutrophication:
Controlling eutrophication by applying algaecides such as copper Sulphate, chlorine etc. on susceptible surface waterbodies.
Removal of the algal bloom by dredging & mechanical means..
Underwater weed cutters mounted on boats can be used to remove rooted aquatic plants.
Dredges can be used to remove sediments to prevent recycling of nutrients and also for deepening of the lake.
Sealing of Lake Bottom with polythene sheeting to prevent release of nutrients from sediments.
Providing aeration artificially to increase the DO levels in the lake water.
Diluting and or flushing the lake with water from Oligotrophic source.
Using Bio remediation techniques.
Arresting of nutrients:
Biological removal using the ability of some microorganism to take up phosphorous in excess of their immediate nutritional requirements and store it within the cells in the form of polyphosphates. The sludge thus formed can be removed from the system.
Water Quality Network
Central Pollution Control Board started national water quality monitoring in 1978 under Global Environmental Monitoring System (GEMS), Water Programme. Monitoring, Programme was started with 24 surface water and 11 groundwater stations. Parallel to. GEMS, a National Programme of Monitoring of Indian National Aquatic Resources (MINARS), was started in 1984, with a total of 113 stations spread over 10 river basins. The present network comprises of 870 stations on rivers, lentic water bodies and subsurface waters are elaborated. The number of locations on mainstream of the major river and their tributaries, medium and minor rivers, lakes, ponds, tanks and other water bodies is given in parenthesis. It is estimated that there is about 45,000 riverine length in India out of which about 6500 km length is having BOD higher than 6 mg/1 and can be branded as polluted, another 8500 km length is moderately polluted having BOD in the range of 3 to 6 Mg/l, and remaining about 30,000 km is relatively clean having BOD of 3 or <3 mg/l . Eighty six polluted water bodies were identified, which need to be prioritized in the restoration programme.
Management of lake
Trophic State Index in Conservation of Lake Ecosystems.
When faced with challenges of trying to describe and organize what is known about the many varied diverse waterbodies, scientists have developed the Trophic State Index (TSI) Classification. This requires minimum data and is generally easy to understand. In the Index total chlorophyll indicates algal biomass and biological productivity: and water clarity is determined by Secchi disc, which indicates the level to which light can penetrate; and algae can photosynthesize. TSI is the best and easy method. The range of the index between 40-50 is usually associated with mesotrophy (moderate productivity); values greater than 50 are associated with eutrophy (high productivity), values less than 40 are associated with oligotrophy (low productivity). Thus, the Trophic State Index (TSI) can serve an important tool in conservation of Lakes.
Assessing the Hydrologic Characteristics of Lake Catchment Using GIS
Land use change is a dynamic process and if anthropogenic it has most often adverse effects on ecological & hydrological processes. For better understanding the impacts of changing physical characteristics on the hydrologic process, geospatial tools like remote sensing and GIS have been found useful.
World Lake Vision
The key to sustainable use of our lakes and wetlands lies in finding a balance between the water needs of human beings and the ability of nature to meet same over the long term. The WLV has articulated the basic action plan for sustainable use of lake and wet land resources in the form of seven basic principles. Seven Principles for the sustainable lake management are related with:-
Harmony between Nature & Man.
Preventive approach to problem solving.
Policy based on sound Science.
Stake holderââ‚¬â„¢s involvement.
If future water security is to be achieved, there is an urgent need to initiate steps for protection, conservation and sustainable use of precious water resources in general and lakes in particular.
Powai Lake A Case Study
The Powai Lake of Mumbai Municipal Corporation of Greater Mumbai (MCGM) is located about 27 Km. away in the North East of Mumbai City. It is an artificial reservoir formed by constructing a masonry dam between two hillocks across the Powai basin in the year 1891. The watershed area of the Powai Lake is 661 hectors. The top level of dam is 58.5 Mtrs. THD (Town Hall Datum), length is about 110 mtrs. and height is varying from 3mtrs.(Min.) to 6.00 Mtrs(Max.).The lake deteriorated due to accelerated growth of residential and commercial premises around the lake and quarrying activities in the catchments area. Also there was no proper control on surrounding. Thus, there was an urgent need to evolve the strategy to improve and maintain the Powai lake surroundings. In the year 1995, under the national Lake Conservation Plan of the Ministry of Environment and Forests (MoEF) Government of India, the Powai Lake of MCGM was reviewed and identified for revival and improvements.
The Powai Lake of Mumbai which was deteriorated due to eutrophication is now recovered using bioremediation and aeration technique.
Observations before the start of revival work and after the completion of the same.
Required value for Eco balance
Value before the start of Work (March 2002)
Values after Completion of the work (April 2003)
10 to 30
0.01 to 0.035
0.1 or less
7 to 8.5
Total Kjeldahl Nitrogen
Total Suspended Solids
10.00 or less
Turbidity in NTU
8 to 25
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