Chapter: Environmental Science and Engineering

Aquatic ecosystems

Aquatic ecosystems deal with biotic community present in water bodies.




v   Aquatic ecosystems deal with biotic community present in water bodies.


v   In terrestrial ecosystem, carbon dioxide & oxygen are present in gaseous form whereas in aquatic ecosystem, these are available in dissolved state.


v   Depending upon the quality and nature of water, the aquatic ecosystem are categorized into:


v   Freshwater Ecosystem and


v   Marine Ecosystem.


Freshwater Ecosystems

v   Freshwater ecosystems cover 0.8% of the Earth's surface and contain 0.009% of its total water.


v   Freshwater ecosystems contain 41% of the world's known fish species.


v   Aquatic ecosystems perform many important environmental functions. For example:


Ø   They recycle nutrients, purify water, attenuate floods, recharge ground water and provide habitats for wildlife.



Ø   Aquatic ecosystems are also used for human recreation, and are very important to the tourism industry, especially in coastal region.

v   There are three basic types of freshwater ecosystems:


q    Lentic: slow-moving water, including Pools, Ponds, and Lakes.


q    Lotic: rapidly-moving water, for example Streams and Rivers.


q   Wetlands: areas where the soil is saturated with water or inundated for at least part of the time


Lakes & pond Ecosystem


v   A pond is a place where living organisms not only live but interact with biotic & abiotic components.


v   Ponds are often exposed to tremendous anthropogenic pressure which significantly affects the system.


v   Lakes are usually big standing freshwater bodies.


v   They have a shallow water zone called Littoral zone; an open water zone where effective penetration of solar light takes place, called limnetic zone and a deep water zone where light penetration is negligible, called Profoundal zone.


I.  Biotic components


1) Producer Organisms


v   It includes submerged, free floating and amphibious macrophytes (like; Hydrilla, Utricularia, Wolfia, Azolla, Typha etc.) and minute floating and suspended lower phytoplanktons (like; Ulothrix, Spirogyra, Oedogonium etc.)


2) Consumer Organisms


a) Primary consumers:These are zooplanktons (ciliates, flagellates, other protozoan, small crustaceans) and benthos.


b) Secondary consumers: These are carnivores like insects and fishes feeding on herbivores


c) Tertiary consumers: These are the large fishes feeding on small fishes.


3) Decomposers Micro organisms like bacteria, fungi and actinomyctes.


II. Abiotic component


v   These are the inorganic as well as organic substances present in the bottom soil or dissolved in water. In addition, to the minerals, some dead organic matter is also present.



Marine or Ocean Ecosystem


v   Marine ecosystems are among the Earth's aquatic ecosystems. They include: Oceans, Estuaries and Lagoons, Mangroves and Coral reefs, the Deep sea and the Sea floor.


v   These are the gigantic reservoirs of water covering approximately 71% of the Earth's surface (an area of some 361 million square kilometers).

v    These ecosystems are different from freshwater ecosystem mainly because of its salty water.


v   The salt concentration in an open sea is usually 3.5% (35 parts per thousand (ppt)). Dominant ions are sodium & chloride.


v   Average temperature of Marine ecosystem is 2-3 degree centigrade, devoid of light.



I. Biotic components


1) Producers It includes phytoplanktons (diatoms, dinoflagillates), large seaweeds (mainly algae like chlorophyceae, phaeophyceae & rhodophyceae; angiosperms like Ruppia, Zostera, posidonia ), and mangrove vegetation (like Rhizophora, Carapa etc.)


2) Consumers


a) Primary consumers: These are herbivores and feed directly on producers (Crustaceans, Mollusks, fish etc.)


b) Secondary consumers: These are carnivorous fishes (Herring, Sahd and Mackerel)


c) Tertiary consumers: These are top carnivorous fishes (Cod, Haddock, etc.)


3) Decomposers These are micro organisms like bacteria, fungi


II. Abiotic components


v   High Na, Ca, Mg and K salt concentration, variable dissolved oxygen content, light & temperature make a unique physiochemical conditions in marine water.



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