In their structure and principle of action, natural ecosystems are open systems. An essential condition for their functioning is the ability to give and receive various types of energy and resources. Without this eternal cycle, the limited resources of the Earth would sooner or later be exhausted. In addition, the ecosystem is considered only the system that can exist without external interference. She produces everything necessary for functioning herself. To maintain a continuous flow of substances in any given ecosystem, functionally different groups of living organisms must be present.
By the size of the occupied territory, as well as the number of elements of animate and inanimate nature involved in the cycle, four types of systems are distinguished. At the very bottom is a microecosystem, the simplest example of which is a drop of human blood or water from a river. Mesoecosystems follow. This category includes the ecosystem of a lake, reservoir, prairie, steppe or, for example, forest. In third place are macroecosystems, which represent entire continents and oceans. And the largest ecosystem is considered to be the planet Earth itself, more precisely - all life on it. This system is called global.
Ecosystem structure
The main source of energy in the lake is sunlight. When rays pass through the water column, plankton absorbs most of the energy, which is then used for photosynthesis. The remaining light is gradually absorbed by the water itself. Therefore, the illumination at the upper levels is always large, and closer to the bottom decreases. Any sufficiently large ecosystem of the lake has a so-called compensation level. This is the depth that the minimum amount of light required by plants reaches. Photosynthesis in such plants slows down to balance other indicators - respiration and food consumption.
The location of the compensation level directly depends on the properties of water, its purity and transparency. It is a kind of conditional dividing line. Above it, plants produce excess oxygen, which is then used by other living organisms. And below the dividing line of oxygen, on the contrary, is too small. Most of it falls into the depths from other, upper layers of water. Thus, only those living organisms that can manage with a minimum amount of oxygen live below the compensation level.
Total distribution of inhabitants
It is obvious that at the upper levels the ecosystem of the lake is populated by a much greater variety of species than in the bottom zone. This fact is due to more favorable conditions for life, the amount of food, heat and oxygen in shallow areas. There are many rooted photophilous plants: lilies, reeds, reeds, arrowheads.
They, in turn, serve as a refuge for insects and arthropods, worms, mollusks, and tadpoles. Also, many fish species find their food here. The smallest arthropods, which require a large amount of light to exist, live near the surface. It also grows free-floating duckweed.
At its lower levels, the lake ecosystem becomes a habitat for various kinds of reducers that feed on dead bodies of animals and plants. There are also many predatory fish species, such as pike and perch, and some invertebrate organisms. These species either feed on dead creatures descending from the upper layers of the water or prey on each other.
Impact of pollution on lake ecosystems
One of the most important natural elements for such systems is phosphorus. The total productivity of the ecosystem depends on its quantity. The natural content of this substance in lake water is small, but human activity leads to a significant increase in concentration. The main reasons include production waste falling into the lake, wastewater discharge, excessive use of fertilizers, which are then washed away by rains and underground streams. All this introduces an excess of phosphorus that is unusual for it into the ecosystem.
As a result, the structure and productivity of a well-functioning system is disrupted: the amount of plankton begins to increase rapidly, from which water acquires a dull greenish tint. The lake begins to bloom, but this is only the first stage. Further, it is polluted by nutrients, water becomes less saturated with oxygen and sunlight (plankton in large quantities absorbs what other inhabitants should have received). The latter disrupts the activity of reducers, due to which the water is filled slowly with rotting remains. At the final stage, plants begin to produce toxins that cause massive death of fish.
Another type of pollution, due to which the lake’s ecosystem is significantly affected, is thermal. At first glance, it does not seem serious: thermal pollution does not add any chemicals to the water. But the normal functioning of the system depends not only on the composition of the medium, but also on temperature. Its increase is also capable of provoking the growth of plants, which triggers a slow but sure fatal reaction. In addition, certain species of fish and invertebrates are adapted to life in a narrow temperature range. An increase or decrease in temperature in this case slows the growth of organisms or kills them.
This type of pollution occurs as a result of human industrial activity. For example, one that uses lake water to cool turbines in factories and power plants.
