Question

Write a short note on the following light zones of Lakes/Sea:

Littoral Zone

Limnetic Zone
Euphotic Zone
Disphotic zone/Twilight zone
Profundal zone

Answer 1

Lakes or sea can be divided into the zones based on how much light penetrates the water. These zones are called the light zones of lakes/sea.

Complete answer:
Littoral zone: The littoral zone is also called the nearshore. This zone is the part of the sea, lake or river which is present close to the shore.This area of the sea or lake or river support the growth of the rooted and benthic plants that are called as the macrophytes.In these areas sunlight penetrate all the way to the sediments.

Limnetic zone: The limnetic zone is also called the pelagic zone.This zone is the open water area where light does not penetrate to the bottom.The limnetic zone is shallower in turbid water than in clear water.
This zone is inhabited mainly by the planktons.This zone is the main photosynthetic zone which produced the oxygen and food.In very small and shallow lakes or ponds the limnetic zone may be absent.

Euphotic zone: The euphotic zone is also called the photic zone, epipelagic zone or sunlit zone.It is the uppermost layer of the sea that receives sunlight.This zone allows phytoplanktons to perform photosynthesis.This zone undergoes a series of physical, chemical and biological processes that supply nutrients into the upper water column.This zone is the home to the majority of aquatic life due to its location.

Disphotic zones/Twilight zone:The middle layer of the sea or lake receives only faint, filtered sunlight during the day time. This is because the sea water absorbs the sunlight.This barely lit zone of ocean or sea or river is called the disphotic zone or twilight zone or mesopelagic zone and this zone appears dark blue in colour.The depth of this zone is dependent upon the clarity of the water.

Profundal zone: The profundal zone is the deep zone of the sea or river or pond. This zone is located below the range of effective light penetration.The profundal zone is the part of aphotic zone.Sediments in the profundal zone comprises silt and mud.This zone is located below the thermocline.

Note: The ocean is divided into these zones to make the oceanographic studies easy. The ocean covers more than 70% of the Earth. Oceans also contain more than 97% water of the total water present on this Earth. Oceans contain salty water.