• An ecosystem in a water body is called aquatic ecosystem.


Classification of aquatic ecosystems based on salt content (parts per thousand – ppt)
Fresh water ecosystems Marine ecosystems Brackish water ecosystems
Less than 5 ppt 35 ppt or above 5 to 35 ppt
Eg. Lakes, ponds, springs, rivers Eg. Seas, oceans Eg. Estuaries, mangroves



Classified on the basis of their zone of occurrence & ability to cross these zones.


Neuston Periphyton Plankton Nekton Benthos
Unattached Attached to stems Locomotive power Swimmers Attached to bottom
Live at air-water interface Live submerged in water Live submerged in water Live under water. Large & powerful Live at bottom of water mass
Eg. Floating plants Eg. Sessile algae Eg. Algae, crustaceans Eg. All sea animals


Factors limiting productivity of Aquatic Habitats:


4 main factors are:


  • Photic zone:
    1. Light penetrates Photosysthesis takes place.
  • Aphotic zone:
    1. Light does not penetrate so plant growth restricted. Only respiratory activity takes place. Known as Profundal zone.

Dissolved Oxygen

  • Escapes water body through air-water interface & respiration of organisms.
  • Oxygen less soluble in warm water. When dissolved oxygen falls below 3-5 ppm, many organisms die.



  • Water temperatures are less subject to change, the aquatic organisms have narrow temperature tolerance limit.



Lake – A large water body with huge area and depth.

  • Lake born from geological or geomorphic process
  • Receive surface run off water or ground discharge
  • Chemicals & minerals mix up
  • Lake begins to age



Snow cover of ice on water body can effectively cut off light, plunging the waters into darkness. Hence photosynthesis stops but respiration continues. Thus, in shallow lakes, the oxygen gets depleted. Fish die, but we won’t know it until the ice melts and we find floating fish. This condition is known as winterkill.



Artificial lakes more than natural lakes.

  • Natural lakes – in Himalayan regions, floodplains of Indus, Ganga and Brahmaputra.
  • Lakes also classified on the basis of salt content.
  • On nutrient content basis they are classified as: – Oligotrophic (very low), Mesotrophic (moderate) and Eurotrophic (high rich).

CLEANING OF LAKES/REMOVAL OF NUTRIENTS TECHNIQUE: Deep water abstraction + Flushing + Algae skimming + Plants to suck nutrients + Harvest fish & macrophytes + Sludge removal + Filters for algae removal.


  • Ameenpur Lake – First Biodiversity Heritage Site: Ameenpur Lake gets the status of the first Biodiversity Heritage Site in the country under the biodiversity act, 2002. it is an ancient man-made lake in a western part of Telangana.
  • Lake ‘Sudarshan’ in Gujarat’s Girnar area was perhaps the oldest man-made lake in India, dating back to 300 BC.
  • Note: Majority of lakes in India are Eurotrophic or Mesotrophic.


  • Water body overly enriched with nutrients, leading to plant life growth.
  • Nitrates and phosphates leached into water bodies from fertilizers, industrial waste, sewage, etc. resulting in algal bloom.
  • The nutrient enrichment of the lakes promotes the growth of algae, aquatic plants and various fauna. This process is known as natural eutrophication.


  • Agricultural runoff, untreated sewage, etc
  • Transportation to the aquatic ecosystem
  • Nutrient accumulation and enrichment
  • Overgrowth of Algae
  • Algal Bloom
  • Algae covering the aquatic surface layer
  • Restricts the sunlight penetration, Diffusion of D.O.
  • Underground aquatic Algae, plant’s die
  • Bacterial Decomposition consumes the available oxygen in the aquatic ecosystem
  • Anoxia condition (Devoid of oxygen)
  • All aquatic organism die due to lack of D.0
  • Degradation of aquatic ecosystem


  • Attributable to one influence
  • Travels directly from source to water
  • Easy to regulate
  • Multiple unknown sources
  • Difficult to regulate



EFFECTS – Toxicity, new species invasion, decreased biodiversity, decrease in species richness and diversity, Toxic Aerosols in micro environment.


  • Restoration and preservation of ecosystems + Create buffer zones for sediments to collect + Nitrogen testing + Industrial waste treatment and efficiency + Reduce livestock densities + Reduce non-point


  • Algal bloom – Excessive multiplying of algae or phytoplankton due to favourable environmental conditions.
  • Harmful algal bloom – When such algal bloom produces toxins, it affects marine organisms thus making it difficult to breathe. Produces – diatoms, cyanobacteria, dinoflagellates, filamentous algae.
  • Blooms can be due to a number of reasons. Two common causes are nutrient enrichment and warm waters.


  • Mechanical disturbance
  • Shading
  • Clogging water & overgrowth
  • Mucus & foam formation
  • Shellfish poisoning
  • Direct lethal toxicity
  • Ambush predation


Are HABs dangerous to fish and humans?

  • Oxygen levels drop, fish suffocate and die.
  • O2 level drops due to decomposition of dead algae.
  • Potent neurotoxins that are produced can enter food web thus reaching animals, fish and even humans.
  • Some toxins become airborne.
  • People tend to breathe aerosolized HAB toxins near the beach.
  • Changes in climate can change severity and impact of HAB events.


  • Transition zones between deep-water and terrestrial habitats
  • g. Lake littorals, marshy or swampy areas.
  • World Wetland Day – 2nd February


Ramsar Convention defines wetland as – “areas of marsh, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water, depth of which at low tides, does not exceed 6 meters.

Recent alterations in Wetland rules 2017:

  • States can alter activities prohibited in wetlands.
  • Delineate wetlands, development of integrated plans.
  • All wetlands except river channels, paddy fields, human-made waterbodies for drinking water, aquaculture, salt production etc. can be notified.


  • NPCA is a single conservation programme for both wetlands and lakes.
  • Centrally sponsored scheme, currently being implemented by the Union Ministry of Environment and Forests and Climate Change.
  • Formulated in 2015 by merging of the National Lake Conservation Plan and the National Wetlands Conservation Programme.
  • NPCA seeks to promote better synergy and avoid overlap of administrative functions.


Functions of wetlands

Habitat to various species, sediment filtration, water purification, pollution control, disaster management, nutrients recycling, ground water recharge, prevents erosion, species diversity, stabilize local climate, natural heritage.
Reasons for depletion

Land use changed for agriculture, sand removal from beds, overgrazing, deforestation, pollution, domestic waste, climate change, agricultural runoff, hazardous industrial waste, aqua culture.

Eutrophication abatement, environmental awareness, afforestation, soil conservation, weed control, artificial regeneration, wildlife conservation, heritage management.


Acc. to NLCP – minimum depth 3 mts Acc. To NLCP – minimum depth < 3 mts
Origin from multiple sources Origin due to Geomorphic processes
Minor water level changes Major water level changes
Small pelagial ratio Large pelagial ratio
No waste treatment occurs Waste treatment occurs
Low productivity High productivity
Low biodiversity High biodiversity
Oligo trophic status Eutrophic status
Does not manage flood control Very significant in managing floods
Thermal stratification No Thermal stratification
Management objectives – Control of eutrophication and High-Water quality Biodiversity conservation Specific Functions


RAMSAR criteria for wetland identification:
  • Sites containing rare or unique wetland types.
  • Criteria based on species and ecological communities
  • Specific criteria based on water birds: If it supports 20,000 or more & if it supports 1% individuals of a single species.
  • Specific criteria based on fish.
  • Ramsar Convention works with the collaboration of the following organizations: International Union for Conservation of Nature (IUCN) + Birdlife International + International Water Management Institute (IWMI) + Wetlands International + Wildfowl & Wetlands Trust (WWT) + WWF International.
Management objectives – Control of eutrophication and High-Water quality



  • India signed in Ramsar, Iran, in 1971
  • There are 42 Ramsar sites in India as of December 2020
  • Sole treaty for particular ecosystem.
  • Includes: lakes, rivers, estuaries, swamps, mangroves, coral reefs, oasis, peatlands, wetlands, deltas, tidal flats, fish ponds, rice paddies, reservoirs and salt pans.




Asan Barrage Uttarakhand 21 July 2020
Kanwar Taal or Kabar Taal Lake Bihar, Begusarai 21 July 2020
Sur Sarovar Uttar Pradesh, Agra district 13 November 2020
Lonar Lake Maharashtra, Buldhana district 13 November 2020
Tso Kar Ladakh, Leh district 17 November 2020



  • A register of wetland sites of international importance where changes of ecological character have occurred, are occurring or likely to occur in future due to pollution or other human interference, etc.
  • Established by Recommendation of the Conference of Contracting Parties (1990).
  • Sites may be added or removed only with approval of Contracting Parties.



  • Chilika Lake, Orissa: Placed in 1993 due to choking at mouth. Removed in 2002. Won Ramsar Wetland Conservation Award for 2002.
  • Loktak Lake, Manipur: Places in 1993 due to deforestation in area & pollution. Currently in Montreux Record as per 2020.
  • Keoladeo National Park, Rajasthan: Placed in 1990 due to water shortage and Unbalanced grazing around. Currently in Montreux Record as per 2020.


  • Areas where river meets the sea (exhibiting gradient in salinity), resulting in mixture of fresh river water with salty ocean water, subject to tidal variations.
  • Conditions for Estuary Formation: (1) rising sea level; (2) movement of sand and sandbars; (3) glacial processes; and (4) tectonic processes.
  • Characteristics: Filter for river water + Traps mud & sands + Semi-enclosed coastal body + Connection with open sea + Salinity range – 0 to 35 ppt + Heavily populated + Little wave action.
  • Biologically most productive region à Receives the high amount of nutrients from fresh and marine water.
  • Flora: homes to unique aquatic plants and animals, such as sea turtles and sea lions, sea catfish, saltworts, eelgrass, salt grasses, cord grasses, sea grass, sedge and bulrush.
  • About 60% of the world’s population living along estuaries and the coast.
  • Benefits of Estuarine ecosystems: Commercial fishing + Ports and harbours + Travel and tourism + Economic and social benefits + Water purification + Breeding hotspot + Recreational and community benefits + Erosion protection + Stores and recycles nutrients.



India has 14 major, 44 medium and 162 minor rivers. Major estuaries occur in the Bay of Bengal region. West- flowing rivers are generally fast-moving ones giving rise to formation of estuaries.

Issues relating to Indian Estuarine Ecosystems:

Modification of catchment areas + Pollution + Recreation & unsustainable tourism + Increased dredging and shipping + unstainable Land-use pattern + Fishing & aquaculture + Climate change.


  • Mangroves are littoral plants like trees and bushes having exceptional capacity for salt water tolerance (Halophytic adaptability), growing below high-water level of spring tides.


  • Evergreen land plants growing on tidal flats, deltas, estuaries, bays, creeks and barrier islands.
  • High adaptation to salinity (Halophytic adaptability) and water logging.
  • Ability to absorb fresh water from saline water and require high solar radiation.
  • Produce pneumatophores/blind roots to overcome respiration problem.
  • Have lenticulate banks that facilitate water loss.
  • Secrete excess salts through leaves or block absorption of salts at their roots.
  • Adventitious roots, also called stilt roots.
  • Reduce inundation and moderate monsoonal tidal floods. + Prevent coastal soil erosion and enhance nutrient recycling. + Source of firewood, medicinal plants and edible plants to locals.
  • Provides employment opportunities.

Mangroves are destroyed and converted for the use of agriculture, aquaculture, fuel, industrial purposes and chemical fertilizers.



  • India houses the largest mangroves of the world; Sunderbans.
  • Sunderbans is home to the Royal Bengal Tiger and crocodiles.
  • Orissa’s Bhitarkanika mangroves is the 2nd largest in the Indian sub-continent.
  • Others are found at Godavari-Krishna deltaic regions of Andhra Pradesh.
  • In Gujarat they are found in Gulf of Kuchchh and Kori creek.
  • Andaman & Nicobar Islands possess diverse undisturbed mangrove flora.
  • Condition of mangroves in some parts of India is improving while in some other places is experiencing degradation.


  • Protect shorelines from storm, hurricane winds, waves, and floods + Prevent erosion by stabilizing sediments with tangled root systems + Maintain water quality and clarity, filtering pollutants and trapping sediments + Provide nursery habitat for many commercial fish.


  • Corals are living animals, which lives in a Symbiotic relationship with ‘zooxanthellae’. Both have a mutual type of relation.
  • There are 2 types of corals: Hard and soft — only hard corals build reefs.
  • Majority coral reefs are found in tropical and sub-tropical water, however there are exceptions of deep-water corals in colder regions.





  • Assist coral in nutrient production through photosynthetic activities.
  • Provide fixed carbon compounds, enhance calcification, mediate elemental nutrient flux.

  • Tissues of corals are clear white.
  • Corals receive coloration from zooxanthellae living within tissues.
Coral Polyp
  • Protects zooxanthellae and supplies carbon-dioxide for photosynthesis.




Most common, contiguous with shore Isolated and discontinuous lying shoreward of offshore reef Linear offshore structures. Run parallel to coastline.

Water body between reef & shore is called ‘lagoon’

Circular or semi – circular reefs, arise from subsiding sea floor platform
Seen in Andamans Seen in Palk Bay, Gulf of Mannar & Kachchh Seen in Nicobar and Lakshadweep Seen in Nicobar and Lakshadweep



Natural protective barriers against storms and soil erosion + Food + Medicine + Tourism + Meteorology + Capture nutrients and plankton from water + Largest biogenic calcium carbonate producer + Home to variety of animals and plants + Sources of new medicines being developed to treat cancer, arthritis, human bacterial infections, Alzheimer’s disease, heart disease, viruses, and other diseases + Tourism & meteorology + More than 1 billion people depend on food from coral reefs.


  • Without algae, coral loses its major source of food, turns white or pale and is more susceptible to diseases and eventually starves to death.
  • Bleaching of corals occur when densities of zooxanthellae decline and/or concentration of photosynthetic pigments within zooxanthellae fall.
  • Global Warming Induced Threats To Corals: Unsustainable fishing + Water Pollution + Marine Debris + Habitat Destruction.
Ongoing bleaching events worldwide:

  • Over 4000 miles of coral reefs in Fiji.
  • Third mass bleaching of Great barrier reef.
  • Port Douglas (severe)


  • TEMPERATURE – Anomalously low and high temperatures induce bleaching
  • SOLAR IRRADIANCE – Bleaching during summers occurs on exposed and shallow-living corals
  • SUBAERIAL EXPOSURE – Sudden exposure to air during sea level drop/tectonic movements affect corals
  • SEDIMENTATION – Few instances of bleaching linked to sediments
  • FRESH WATER DILUTION – Though rare, rapid dilution from storm surges and runoffs cause bleaching
  • INORGANIC NUTRIENTS – Increase in ambient elemental nutrient content indirectly causes bleaching
  • XENOBIOTICS – Exposure to chemicals like Cu, herbicides and oil leads to zooxanthellae loss
  • EPIZOOTICS – It is a type of pathogen induced bleaching

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