 Now, we are going to talk about the aquatic ecosystems, aquatic ecosystems, ecosystems present in water. We know that this ecosystems which are present in water, the water have to support the life and all the factors which are affecting upon the water will be affecting the living forms, the life forms. Water have certain specific properties. Aquatic ecosystem whether it consists of a marine, marine ecosystem that is the sea or it is a freshwater ecosystem like a pound or a lake or maybe a stream, water is the major component. These are the some important characteristics of water which are responsible for supporting life or for the presence of a specific form of life inside that ecosystem. Water changes its temperature slowly. Water do not change its temperature like air quickly. Now, this is a property which is helpful or more appropriate for life because sudden changes and quick changes in temperature are difficult for organisms to accommodate. So, it means that water is a good or more supportive form of an ecosystem for the organisms and for the life. This is the reason that most of the forters, lakes, the oceans, seas, they have a huge biodiversity in themselves. Water absorbs considerable amount of light energy, water even a very clear water or even a very unclear water. They absorb a considerable form of energy in the form of light, the sunlight and that sunlight we know is the entry point of energy in an ecosystem. This is the reason that many plants and other organisms which can carry out photosynthesis can sustain their life in the water very well. But there is a problem with it that in the upper layers of water light penetration is always good but in the lower layers of water usually light penetration is reduced. This is a problem for living organisms because in the lower parts of the water body ocean or lake or pond light penetration is less than its normal level and may be this is not supportive for photosynthesis to occur. And if this is difficult to carry out the photosynthesis then the producers will not be able to make food and they will not be able to make energy. This will result in no energy in the coming in the ecosystem and result will be a dead ecosystem ultimately. There is another thing that nutrients are usually concentrated at bottom because everything which is present in an ecosystem in a water ecosystem the organisms they are parts like fallen leaves of the plants or the dead organisms all of them will go and settle into the bottom. So, bottom is rich in nutrients water the bottom have not much organic nutrients mostly the beds of the water ecosystems have good diverse life forms. Water is abundantly available in this ecosystem the benefit water is a limiting factor this is very very important and because ecosystem itself consists of water so water is abundantly available. So, aquatic ecosystems are usually very very supportive for life forms but just there is a problem on the base then the light penetration is low. We take an example of a freshwater lake freshwater lakes they vary in nutrients in the physical conditions and their depths. Water lakes sometimes may be very very deep several meters deep sometimes they are quite shallow but they have and life which is present inside the lakes is according to the conditions present in a lake. If we consider a lake it consists of three major zones zones of a lake are literal zone the lymnatic zone and the profundal zone literal zone is the zone of shallow water the water from the bank of that particular lake and going down towards the depth but which is still shallow. In the shallow water this is the benefit that light penetrates till the bottom. The photosynthetic organisms can grow very well in this particular area. So, there is a rich diversity of organisms present inside this zone. So, phytoplankton which are small organisms which are photosynthetic and they can they can produce food and they can convert sunlight energy into chemical energy and then the consumers the zooplankton small animal forms which eat upon the phytoplankton the plant plant like organisms then the fishes which can eat upon both of these. Then the carnivore fishes which can eat upon those herbivore fishes then comes the next zone when the lake is deep it consists of two major zones lymnatic zone in the profundal zone lymnatic zone the top most layer in which the penetration of sunlight is sufficient to support photosynthesis again the plant life exist and the phytoplankton the plant like organisms they exist a lot they are very diverse they carry out photosynthesis and they produce food and they also produce the energy for other life forms. Then there are other organisms like crustaceans small insects the water insects which feed upon the phytoplankton or some plants we have submerged plants like for example lotus the leaves are on the top and their branches are inside. So different types of other plants like this which are fully or partially submerged they are present in this zone and they can carry out photosynthesis very well. And there are zooplankton which eat upon these like insects small crustaceans and then there are fish the herbivore fish which eat upon these plants and there may be large size fish or may be the carnivore fish which hunt upon these fishes which are herbivore so there is a long food chain there is a diverse form of there are diverse forms of life present in the lymnatic zone then comes the profundal zone this is the zone at the depth in this zone from depth to the bottom say about middle of the lake to the bottom of the lake in this zone light penetration is not good enough to support photosynthesis. So this is difficult for the producers to live in this particular area in this particular area a specific type of organisms particularly the bacteria can live which are called chemotrophs these bacteria can convert inorganic chemicals and utilize the energy present in the inorganic chemicals to make their food and their energy we call them chemotrophs they do not require sunlight as energy source rather they use inorganic chemicals or sometimes organic chemicals as their energy source and convert these into chemical form of energy and their food we call them chemotrophs then the decomposers can survive very well in this in this zone because we know that the bottom of the lake will have all of the dead parts of the organisms they will have all the dead organisms settled in their on their base so the decomposers can survive very well in this last zone the profundal zone. So this is also rich in biodiversity it have more of decomposers more of the animal like organisms we can say and more of the chemotrophs. So a lake is divided into these three zones shallow zone the deep zone and deep zone is further divided into the top layer lemnatic zone in which light penetration is good and the profundal zone the base zone in which light penetration is not sufficient to support the photosynthesis and in all of these zones the life which are the living organisms which are present are just according to these properties of these areas. Now the human interference human always interfere with the ecosystems humans because water bodies are always see we can say interfered or enriched by human we can say produced materials the agricultural runoff waters. So when humans enter their different types of runoffs even the industrial waste waters we throw all the industrial waste waters into the rivers and the lakes these results in a situation called eutrophication this results in a very huge growth of some cyanobacteria cyanobacteria also called blue green algae which carry out photosynthesis because in the top layer the light energy is available in excess so they grow very well when they grow very quick they produce a scum on the surface of the water body that is they grow so much that they cover the surface of the water body and this results in no oxygen almost no or very very less quantity of oxygen penetrating inside and availability of food to the other producers is also affected availability of sunlight to the other producers also affected because the surface is covered the result is that all the other plants the animal life forms the crustaceans the fish they start dying and in some time the life forms other than these cyanobacteria they die when they die they go and settle into the bottom when they go and settle into the bottom then more and more decomposers they grow inside when they grow inside they break up all these dead organic bodies of dead materials the bodies of the organisms they even provide more food for these cyanobacteria and the other decomposers the result is destruction of the habitat which results in we can say destruction of the whole ecosystem only a few types of life forms are then present there and all the other lives the diversity of life is gone and this results in instability of the ecosystem and the whole ecosystem is destroyed there are lot many lakes in the world and pounds usually which are destroyed like this now we are going to talk about the terrestrial ecosystem terrestrial ecosystems are the ecosystems present on land from as we know that evolution theory says that life was existing initially in waters and then it was transferred to land the organisms adapted certain characteristics in transition from water to land the animals they produce skeleton skeleton is the hard framework of the body that supports actually organisms on the land in the plants they have vascular bundles these vascular bundles also provides them sort of a skeleton which allow them to stand straight on the earth the second important thing is this that water is essential for life and water is not very sufficient in a land or in a terrestrial ecosystem so water is a limiting factor all the organisms plants and animals adapted to conserve water to the maximum now we talk about some major terrestrial ecosystems terrestrial ecosystems are divided into four major categories throughout the world forest ecosystem forest ecosystem is itself further divided into some different types the tropical rain forest the temperate deciduous forest and the coniferous alpine and boreal forest the second type is a grass land ecosystem then comes the desert ecosystems and then comes the tundra tundra very very cold ecosystems so terrestrial ecosystems are divided into four categories the forest the grass lands the deserts and the tundra pakistan is rich in biodiversity and rich in ecosystems we are present in that area where we have forest we have grass lands we have deserts and even we have tundra