9, 10 Lake Ecology and Eutrophication; Wetlands Ecosystem UPSC Notes | EduRev

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Any body of standing water, generally large enough in area and depth, irrespective of its hydrology, ecology, and other characteristics is generally known as lake.

Ageing of Lakes

The nutrient enrichment of the lakes promotes the growth of algae, aquatic plants and various fauna. This process is known as natural eutrophication.

Similar nutrient enrichment of lakes at an accelerated rate is caused by human activities and the consequent ageing phenomenon is known as 'cultural eutrophication'.

In India, natural lakes (relatively few) mostly ile in the Himalayan region, the floodplains of Indus, Ganga and Brahmaputra.

Lake 'Sudarshan' in Gujarat's Girnar area was perhaps the oldest man-made lake in India, dating back to 300 BC.

Lakes are also classified on the basis of their water chemistry. Based-on the levels of salinity, they are known as Freshwater, Brackish or Saline lakes (similar to that of classification of aquatic ecosystem).

On the basis of their nutrient content, they are categorized as Oligotrophic (very low nutrients), Mesotrophic (moderate nutrients) and Eutrophic (highly nutrient rich).

Removal of the nutrients from a lake 

  • Flushing with nutrient-poor waters.
  • Deep water abstraction.
  • On-site P-elimination by flocculation/flotation with water backflow, or floating Plant
  • NESSIE with adsorbents.
  • On-site algae removal by filters and P-absorbers.
  • 0n-site algae skimming and separator thickening.
  • Artificial mixing / Destratification (permanent or intermittent).
  • Harvest of fishes and macrophysics. 
  • Sludge removal



A syndrome of ecosystem, response to the addition of artificial or natural substances such as nitrates and phosphates through fertilizer, sewage, etc. that fertilize the aquatic ecosystem.

The growth of green algae which we see in the lake surface layer is the physical identification of an Eutrophication.

Some algae and blue-green bacteria thrive on the excess ions and a population explosion covers almost entire surface layer is known as algal bloom.  Nitrogen testing is a technique to find the optimum amount of fertilizer required for crop plants. It will reduce the amount of nitrogen lost to the surrounding area.


Algae or phytoplankton are microscopic organisms that can be found naturally in coastal waters. They are major producers of oxygen and food for many of the animals that live in these waters.

Algal blooms can be any colour, but the most common ones are red or brown.

Most algal blooms are not harmful but some produce toxins and do affect fish, birds, marine mammals and humans. 

Use of algae 

Most species of algae or phytoplankton serve as the energy producers at the base of the food web, without which higher life on this planet would not exist.

Why Red Tide is a misnomer?

"Red Tide" is a common name for such a phenomenon where certain Phytoplankton species contain pigments and "bloom" such that the human eye perceives the water to be discoloured. Blooms can appear greenish, brown, and even reddish orange depending upon the type of organism, the type of water, and the concentration of the organisms.

The term "red tide" is thus a misnomer because blooms are not always red, they are not associated with tides, they are usually not harmful, and some species can be harmful or dangerous at low cell concentrations that do not discolour the water.

What are the causes of these blooms? 

Two common causes are nutrient enrichment and warm waters.



Areas of marsh, fen, peat land/water, whether natural (or) artificial, permanent (or) temporary with water that is static (or) flowing, fresh, brackish (or) salt, including areas of marine water the depth of which at low tide does not exceed 6 mitres.

Wetlands Classification- 

1. Inland wetland- 

A) Natural- Lakes / Ponds, Ox-bow Lakes, Waterlogged, Swamp/marsh

B) Manmade- Reservoirs Tank, Ash pond

2. Costal Wetland-

A) Natural- Coral reef, Tidal flat, Mangroves, Salt marsh, Estuary, Lagoon, Creek, Backwater, Bay

B) Manmade -• Salt pans, Aquaculture

Functions of Wetlands-

  • Habitat to aquatic flora and fauna, birds
  • Filtration of sediments and nutrients from surface water,
  • Nutrients recycling, Water purification Floods mitigation, 
  • Ground water recharging, Buffer shorelines against erosion,
  • Genetic reservoir for various species of plants(rice)
  • the National Lake Conservation Programme (NLCP) considers lakes as standing water
  • Bodies which have a minimum water depth of 3 m, generally cover a water spread of more than ten hectares, and have no or very little aquatic vegetation.
  • Wetlands (generally less than 3 m deep over most of their area) are usually rich in nutrients (derived from surroundings and their sediments) and have .abundant growth of aquatic macrophysics

India's Wetland

    Wetlands occupy 18.4% of the country's area of which 70% are under paddy cultivation.

    Inland wetlands >Costal Wetlands

National Wetlands Conservation Programme (NWCP)

  • NWCP was implemented in the year 1985-86. 
  • Under the programme, 115 wetlands have been identified by the Ministry which require urgent conservation and management interventions.


  • Conservation of wetlands to prevent their further degradation and ensuring their wise
  • Use for the benefit of local communities and overall conservation of biodiversity.


  • To lay down policy guidelines for conservation and management of wetlands in the country. 
  • to provide financial assistance for undertaking intensive conservation measures in the identified wetlands
  • The Central Government is responsible for overall coordination of wetland
  • Conservation programmes and initiatives at the international and national levels. It also provides guidelines, financial & technical assistance to state govt. 
  • State Governments/UT Administration are responsible for management of wetlands and implementation of the NWCP for ensuring their wise-use

Criteria for Identification of Wetlands of National Importance 

Criteria for identification of wetlands of national importance under NWCP are same as those prescribed under the 'Ramsar Convention on Wetlands' and are as given below:

1. Sites containing representative, rare or unique wetland types

    Example of a natural or near-natural wetland type' found within the appropriate biogeographic region.      

2. Criteria based on species and ecological communities

  • If it supports vulnerable, endangered, or critically endangered species; or
  • Threatened ecological communities.
  • If it supports populations of plant and/or animal species important for maintaining the biological diversity of a particular biogeographic region.
  • If it supports plant and/or animal species at a critical stage in their life cycles, or provides refuge during adverse conditions.

3. Specific criteria based on water birds

  • If it regularly supports 20,000 or more water birds.
  • If it regularly supports 1% of the individuals in a population of one species or subspecies of water birds.    

4. Specific criteria based on fish

  • If it supports a significant proportion of indigenous fish subspecies, species or families, life-history  stages,  species  interactions  and/or  populations  that  are representative of wetland benefits and/or values and thereby contributes to global biological diversity.
  • If it is an important source of food for fishes, spawning ground, nursery and/or migration path on which fish stocks, either within the wetland or elsewhere, depend.

5. Specific criteria based on water/life and culture

  • If it is an important source of food and water  resource, increased possibilities for recreation  and eco-tourism, improved scenic values, educational opportunities, conservation of cultural heritage (historic or religious sites)
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