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1. Sunlight
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- As sunlight travels downward through a water column, its intensity quickly fades. The depth to which light can penetrate in a lake directly influences how far plant life can spread.
- Based on this light availability and plant presence, aquatic environments are divided into two main zones: the photic zone, where light supports photosynthesis, and the aphotic zone, where light is too limited for plant growth.
(a) Photic zone
- This is the uppermost layer of an aquatic ecosystem where sunlight can reach, allowing photosynthesis to occur. All photosynthetic activity in water bodies is restricted to this light-filled zone.
- The depth of this zone depends on the transparency of water, photic (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.
(b) Aphotic zone
- The lower layers of the aquatic ecosystems, where light penetration and plant growth are restricted forms the aphotic zone.
- Only respiration activity takes place. (photic-both respiration and photosynthesis take place).
- Aphotic zone is positioned below the littoral and photic zones to bottom of the lake where light levels are too low for photosynthesis.
- This deep, unlit region is also known as the profundal zone.
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2. Dissolved oxygen
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- Oxygen enters the aquatic ecosystem through the air water interface and by the photosynthetic, average concentration of dissolved oxygen as 10 parts per million by weight.
- Dissolved oxygen escapes the water body through air-water interface and through respiration of organisms (fish, decomposers, zooplanktons, etc.).
- The amount of dissolved oxygen retained in water is also influenced by temperature.
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Other limiting factors which influence on Aquatic productivity
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(i) Transparency
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- Transparency affects the extent of light penetration.
- Suspended particulate matters such as clay, silt, phytoplankton, etc. make the water turbid. Consequently it limits the extent of light penetration and the photosynthetic activity in a significant way.
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(ii) Temperature
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- The water temperature changes less rapidly than the temperature of air because water has a considerably higher specific heat than air.
- Since water temperatures are less subject to change, the aquatic organisms have narrow temperature tolerance limit.
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