Perhaps now even children know that the chemical formula of water is H 2 O. However, this is a theory, but in fact a huge amount of substances of both organic and inorganic origin are dissolved in water. Pure water, as you know, has no taste or smell, but anyone can make sure that in the vast majority of cases this is not so. Drinking water, for example, contains a certain amount of mineral salts, which gives it a salty taste. To one degree or another, it contains everything that it comes into contact with. The exact composition of the water depends on the place of its intake, because in different places it comes into contact with different substances. In some places, chemists will find heavy metals in liquids, somewhere - various organic substances.
How does this happen?
Water is a universal solvent. Distilled water is considered to be the purest substance in the chemical sense, but after a while it loses its original state. And here's why: water is such a good solvent that over time, molecules of various substances from the air get into it. In nature, this also happens due to the vital activity of various organisms living in the aquatic environment.
Gases in the water
Pouring water into a glass, you can see gas bubbles that will be on the walls of the vessel. Along with salts and other substances, water dissolves gases in itself. First of all, it is nitrogen from the air, as well as oxygen, carbon dioxide, and in some cases methane and hydrogen sulfide. Moreover, cold water dissolves gases much better than warm, so the lower the temperature, the higher the concentration of gases. And vice versa - with increasing temperature, solubility decreases.
Sources of gases dissolved in water
But where do all these substances come from in water? Nitrogen, as a rule, dissolves in the process of interaction with the atmosphere, methane - as a result of contact with rocks and decomposition of bottom sludge, and hydrogen sulfide is formed as a product of decay of organic residues. As a rule, hydrogen sulfide is contained in deep water layers and does not rise to the surface. With its high concentration, life is impossible, for example, in the Black Sea at depths of more than 150-200 meters, due to the high water saturation with hydrogen sulfide, there are almost no living organisms, except for some bacteria.
Oxygen is also always found in water. It is a universal oxidizing agent, therefore, partially decomposes hydrogen sulfide, reducing its concentration. But where does the oxygen in the water come from? Talk about him will be special.
Oxygen
Almost all living organisms need oxygen. People breathe air, which is a mixture of gases, a considerable part of which is it.
Inhabitants of the aquatic environment also need this substance, so the concentration of oxygen in water is a very important indicator. Usually it is up to 14 mg / l, when it comes to natural waters, and sometimes even more. The same liquid that flows from the tap contains much less oxygen, and this is easy to explain. After water intake, tap water goes through several stages of purification, and dissolved oxygen is an extremely unstable compound. As a result of gas exchange with the air, most of it simply disappears. So where does the oxygen in the water come from, if not from the air?
In fact, this is not entirely true, it is also taken from the air, but its fraction, dissolved as a result of contact with the atmosphere, is extremely small. In order for the interaction of oxygen with water to be sufficiently effective, special conditions are necessary: low temperature, high pressure and relatively low salinity. They are far from always observed, and life would hardly exist in its current form if the only way to form this gas in the aquatic environment was through interaction with the atmosphere. Fortunately, there are two more sources where oxygen in water comes from. Firstly, dissolved gas molecules are found in large quantities in snow and rainwater, and secondly, this is the main source as a result of photosynthesis by aquatic plants and phytoplankton.
By the way, despite the fact that the water molecule contains oxygen, living organisms, of course, are not able to extract it from there. Therefore, it remains for them to be content with the dissolved fraction.
About the value of algae
In ordinary life, few people wonder what we breathe and why the composition of the air is exactly what it is. Almost everyone knows that most living organisms breathing air are adapted to such a mixture. But if we are talking about the ground-air environment, then no questions arise. And where does the oxygen come from? Like on earth, there are many plants that, through a process called photosynthesis, consume light and carbon dioxide and produce O 2 .
To be more precise, in recent decades, for one reason or another, humanity has destroyed a huge part of the forests. But there is no talk of a global crisis, although the world's population is constantly growing, and oxygen consumption
huge. And algae that live in the oceans are of great importance in this matter, for the most part it is due to them that the water is saturated with oxygen. People and marine life eat some of their species, but their quantity remains sufficient for effective photosynthesis. This is where the oxygen comes from in the water, which means thanks to gas exchange with the atmosphere and in the air. It is photosynthesis of algae that is its main source. By the way, it was due to the processes occurring in plants that primary oxygen was accumulated in the atmosphere, and now only its constant composition is being maintained.
The role of dissolved oxygen (PK)
Despite the fact that the respiratory system of aquatic inhabitants is arranged differently than that of residents of the air-ground environment, they need all the same substances. First of all, we are talking about oxygen, which plays an important role in the life of the vast majority of organisms. And if we extract it from the atmosphere, where its share is more or less stable and amounts to about 21%, then the inhabitants of rivers, seas and oceans are highly dependent on how much oxygen in the water is contained in their habitat. In addition to fish, plants also need oxygen. However, its products are usually higher than the level of consumption, so this should not cause concern.
Normal performance
Due to its significant role in the normal functioning of ecosystems, the level of the Republic of Kazakhstan is often monitored by biologists and ecologists. Indeed, everything is connected in nature, the violation of the gas balance in one pond can cause problems in neighboring ones, if they are connected. As a rule, measurements are carried out before noon, during this period the gas concentration in surface waters becomes maximum and amounts to 14 mg / l. This indicator is subject to serious daily and seasonal fluctuations, but it should not fall below 4 mg / l.
A decrease in concentration to 2 mg / L or less causes a mass death of the inhabitants of the hydrosphere. In fact - from suffocation. A gradual decrease in the indicator may indicate a pollution of the reservoir and may also eventually result in the death of water inhabitants.
RC in artificially created ecosystems
Good aeration is important, for example, in the aquarium. That is why it is necessary not only to install special pumps that pump air into the water and saturate it with oxygen, but, for example, if necessary, plant various algae at the bottom. Of course, those who have such a hobby are primarily interested in the aesthetics of the ecosystem, but we must not forget about its sustainability and a certain durability.
If we are talking about fisheries, pearl production and other specific industries of this type, then in addition to various measures aimed at maintaining a sufficient concentration of dissolved oxygen in water, it is necessary to regularly measure this indicator using special samples. When sampling them, it is extremely important that there is no contact with air, this can distort the analysis results.