Aquatic ecosystems refer to plant and animal communities occurring in water bodies

Classification of aquatic ecosystem

1. Fresh water ecosystems

• The salt content of fresh bodies is very low, always less than 5 ppt (parts per thousand).

It is subdivided as follows-

Still water/Lentic ecosystem-

• In this ecosystem the water remains stationary at any place for longer time.

• Example- Lake, ponds etc.

Flowing water/Lotic ecosystem-

• In this ecosystem water does not remains stationary at any place.

• Example- Streams, Rivers etc.

2. Marine ecosystems 

• The water bodies containing salt concentration equal to or above that of sea water (i.e.,35 ppt or above).

• Coral reefs are very rich in species and are found in only a few shallow tropical seas.

• The richest coral reefs in India are around the Andaman and Nicobar Islands and in the gulf of Kutch.

• Example- shallow seas and open ocean.

3. Brackish water ecosystems

• Brackish water ecosystems refer to water bodies with a salt content ranging from 5 to 35 ppt.

• They are known for their high biomass production and are considered among the most productive ecosystems in the world.

• The Sundarbans in the delta of the Ganges is home to the largest mangrove swamps.

• Examples of brackish water ecosystems include estuaries, salt marshes, and mangrove swamps and forests.

4. Lake ecosystem

• Lakes are inland, depressions containing standing water. They vary considerably in area and depth.

Characteristics of Lake Ecosystem

• The gradations of temperature, sunlight and oxygen are directly responsible for vertical zonation or stratification occurring in lakes.

These are of 3 types of Stratification

I. Thermal stratification.

II. Light Stratification.

III.Oxygen Stratification.

I. The thermal stratification

• The thermal stratification of lakes is a natural phenomenon that occurs when the temperature changes at varying depths within a body of water.

• This change in temperature is caused by the water's density, which varies with temperature.

A. Summer Stratification

• Thermal stratification is fairly pronounced during the summer seasons in most lakes of the temperate (cold) regions but is rare in lakes of tropical (hot) and subtropical regions where it occurs only in very deep lakes.

• This is so, because the rate of mixing of layers is very fast in case of tropical lakes whereas, the temperate lakes retain well defined layers showing different temperature.

• These layers do not mix rapidly. Therefore, the temperate lakes exhibit clear stratification with respect to temperature

Thermal stratification is maximum during the summer season, primarily due to two reasons-

• Firstly, due to the fact that solar intensity increases during this period and it heats the surface layer greatly while the lower layers remain comparatively cool.

• Secondly, the thermally stratified layers offer resistance to mixing by wind.

Different layers of stratified lakes-

Epilimnion -

• The Epilimnion refers to the uppermost layer of a lake, characterized by warm water that circulates freely and receives ample light. However, it contains relatively low levels of nutrients.

• Most of the phytoplankton’s grow in the epilimnion which is well aerated both due to photosynthetic oxygen production by plants and mixing by wind.

Metalimnion –

• The metalimnion is a layer of water in a lake or other body of water that is situated between the epilimnion and the hypolimnion. It is considered an intermediate layer that typically does not undergo much mixing or circulation.

Hypolimnion –

• The Hypolimnion is the deep, cold, and non-circulating bottom layer of a body of water.

• It is a zone with low oxygen content due to the decomposition process that utilizes it.

• Despite the low oxygen content, the Hypolimnion is rich in nutrients.

B. Winter Stratification

• During extremes of winter the surface layer of the lake freezes or attains a temperature close to O degree Celsius.

• Under these conditions an inverse stratification develops.

• During winter, the water beneath the ice in a lake absorbs solar radiation passing through the ice and remains relatively warm.

• Once this warm water reaches a temperature of 4°C, it becomes denser and heavier, causing it to sink to the bottom of the lake.

• As the warm water sinks, it mixes with the bottom water of the lake, which is heated by heat conducted from the bottom mud.

• This process results in a higher temperature at the bottom of the lake, while the overall stability of the water remains undisturbed.

 Overturn –

• The summer or winter stratification is seasonal. Circulation of lake water occurs twice a year, in the spring and autumn seasons by a process called overturn.

• This circulation is important for lakes which undergo stratification as it allows thorough mixing of oxygen, phytoplankton and nutrients within the lake.

II. Light Stratification

• The penetration of light in water bodies is limited depending on the transparency of water and its ability to absorb light.

On the basis of light penetration lakes become vertically stratified into two basic layers

• Photic zone-This is the uppermost zone where light penetration is most dominating.

• Tropholytic zone – This is the zone where decomposition is most active and which corresponds to the aphotic zone.

• Compensation depth - The depth at which light intensity is such that the photosynthetic production is just enough to balance respiratory losses and beyond which light penetration is so low that it is no longer effective. It is the length between the above stated 2 zones.

III. Oxygen Stratification-

• This stratification is parallel to temperature stratification is summer time.

• The amount of oxygen is greatest on the surface, gradually decreasing with depth.

Division/Zones of Lake

1. Littoral zone -

• This is the shallow water zone, near the shore, where light penetrates to the bottom. Rooted plants can grow only in this region.

 Plants-

• Non-rooted phytoplankton which include all kinds of algae.

• All rooted or benthic flowering plants, attached to the substratum.

Animals-

• Animals of this zone may be herbivores, carnivores or detritus feeders and are as diverse as plant.

• Zooplankton- Crustaceans. Cladocerans , Rotifers etc.

2. Open Water Zone/Limnetic Zone –

• The Open Water Zone or Limnetic Zone is located beyond the littoral zone.

• The area is too deep for light to penetrate to the bottom, and rooted plants cannot grow in this region.

• The Limnetic region of the zone is characterized by light penetration and the distribution of organisms based on light availability.

• This zone is often referred to as the "photic" zone due to the availability of light.

Plants-

• Dinoflagellates, blue green algae etc.

Animals-

• Zooplankton, Nekton etc.

Profundal region

• It is Aphotic zone.

• No plants are found in this region.

Animals-

• Chemoautotrophs (bacteria and fungi etc.), Heterotrophs (Carnivorous zooplankton etc.).

3.Benthic Zone –

• This forms the floor of the lake and underlies the littoral and limnetic zone.

Types of Lakes

1. Oligotrophic -

• It is a nutrient poor lake.

2. Eutrophic -

• It is a nutrient rich Lake.

3. Mesotrophic –

• It is a medium nutrient lake.

Comparison of these Lakes-

Some facts about Lakes

• Lake Baikal (Located in Siberia, Russia) is the deepest lake in the world and also the largest freshwater lake by volume in the world.

• Lake Tanganyika (Africa) is the longest lake of the world.

• Largest freshwater lake in India – Wular Lake, Jammu and Kashmir

• Largest Saline water lake in India – Chilka Lake, Orissa.

• Highest lake in India (Altitude) – Cholamu lake, Sikkim.

• Longest Lake in India – Vembanad lake, Kerala.

• Largest Artificial Lake in India – Govind Vallabh Pant Sagar (Rihand Dam).

One Liner Questions on Lake Ecosystem.

What are aquatic ecosystems?

Aquatic ecosystems are plant and animal communities that occur in water bodies such as oceans, rivers, lakes, and ponds.

How are aquatic ecosystems classified?

Aquatic ecosystems are classified into four types: freshwater, marine, brackish water, and lake ecosystems.

What is a freshwater ecosystem?

A freshwater ecosystem is a type of aquatic ecosystem with a salt concentration of less than 5 ppt, and it includes still water and flowing water ecosystems.

What is a marine ecosystem?

A marine ecosystem is a type of aquatic ecosystem with a salt concentration equal to or above that of sea water (i.e., 35 ppt or above).

What is a brackish water ecosystem?

A brackish water ecosystem is a type of aquatic ecosystem with a salt content ranging from 5 to 35 ppt.

What are the characteristics of a lake ecosystem?

Lakes are inland, depressions containing standing water, and they vary considerably in area and depth. The gradations of temperature, sunlight, and oxygen are directly responsible for vertical zonation or stratification occurring in lakes.

What are the three types of stratification occurring in lakes?

The three types of stratification occurring in lakes are thermal stratification, light stratification, and oxygen stratification.

What is thermal stratification?

Thermal stratification is a natural phenomenon that occurs when the temperature changes at varying depths within a body of water. This change in temperature is caused by the water's density, which varies with temperature.

What is light stratification?

Light stratification is the stratification that occurs in water bodies based on the penetration of light.

What is oxygen stratification?

Oxygen stratification is the stratification that occurs in water bodies parallel to temperature stratification in summer time.

What are the types of freshwater ecosystems?

Freshwater ecosystems are subdivided into still water (lentic) and flowing water (lotic) ecosystems.

What is the difference between still water and flowing water ecosystems?

In still water (lentic) ecosystems, the water remains stationary at any place for a longer time, while in flowing water (lotic) ecosystems, the water does not remain stationary at any place.

What are the characteristics of a marine ecosystem?

Marine ecosystems are water bodies containing salt concentration equal to or above that of sea water (i.e., 35 ppt or above). Examples of marine ecosystems include shallow seas and open ocean.

What are the characteristics of a brackish water ecosystem?

Brackish water ecosystems refer to water bodies with a salt content ranging from 5 to 35 ppt. They are known for their high biomass production and are considered among the most productive ecosystems in the world.

What are the three types of layers in a lake ecosystem?

The three types of layers in a lake ecosystem are the epilimnion, the metalimnion, and the hypolimnion.