Shankar IAS Test: Aquatic Ecosystem- 1 - UPSC MCQ

Aquatic Organisms: The aquatic organisms are classified based on their zone of occurrence and their ability to cross these zones. The organisms (both flora and fauna) in the aquatic ecosystem are unevenly distributed.

Periphyton: These are organisms which remain attached to stems and leaves of rooted plants or substances emerging above the bottom mud such as sessile algae and their associated group of animals.

Photic zone:

• It is the upper layer of the aquatic ecosystems, up to which light penetrates and within which photosynthetic activity is confined.

• The depth of this zone depends on the transparency of water.

• Both photosynthesis and respiration activity takes place.

• The Phototic (or “euphotic”) zone is the lighted and usually well-mixed portion that extends from the lake surface down to where the light level is 1% of that at the surface.

• The water temperature changes less rapidly than the temperature of air because water has a considerably higher specific heat than air, i.e. larger amounts of heat energy must be added to or taken away from water to raise or lower its temperature.

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

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

•  An oligotrophic lake or water body is one which has a relatively low productivity due to the low nutrient content in the lake.

• Eutrophic lake: a lake with high productivity, high nutrients and with dark water. The water is usually not good for drinking purpose.

•  Vast majority of lakes in India are either eutrophic or mesotrophic because of the nutrients derived from their surroundings or organic wastes entering them.

• Eutrophication eventually creates a detritus layer in the ponds & lakes and produces a successively shallower depth of surface water.

• Eutrophication may cause the ecosystem to become competitive by transforming the normal limiting nutrient to an abundant level. This causes shifting in species composition of ecosystem Toxicity.

• A decrease in water transparency and increased turbidity. • Affects navigation due to increased turbidity.

• Increased biomass of inedible toxic phytoplankton.

• Increase in the bloom of gelatinous zooplankton

• Increased biomass of benthic and epiphytic algae

• Unsuitable for aesthetic recreation, and reduction in the value of water body

• Nitrogen testing & modelling

• N-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.

• Treatment of Industrial effluents

• Organic farming & Integrated Farming System.

• Reduction in livestock densities

• It has a free connection with the open sea.

• The complete salinity range from 0-35 ppt is seen from the head (river end) to the mouth (see end) of an estuary.

• An estuary has very little wave action, so it provides a calm refuge from the open sea.

• It provides the shelter for some of the animals.

• The mangroves of Sundarbans are the largest single block of tidal halophytic mangroves of the world.

• The mangroves of Bhitarkanika (Orissa), which is the second largest in the Indian subcontinent, harbour high mangroves found in Gulf of Kachchh, to taller stands found in the Sunderbans.

• On the Andaman & Nicobar Islands, the small tidal estuaries, neritic inlets and the lagoons support a dense and diverse undisturbed mangrove flora.