Where does oxygen in the water come from? Interaction of oxygen with water. Oxygen saturation of water

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, both organic and inorganic, is dissolved in water. Pure water, as is known, has no taste and smell, but anyone can be convinced that in the overwhelming majority of cases it is not so. In drinking water, for example, contains a certain amount of mineral salts, which gives it a salty taste. To some extent, it contains everything that it contacts. The exact composition of the water depends on the location of its fence, because in different places it is in contact with different substances. In some places, chemists will find heavy metals in the liquid, somewhere - various organic substances.

How does it work?

Water is a universal solvent. Distilled water is considered the most pure substance in the chemical sense, but after a while it loses its original state. And this is why: water is such a good solvent that eventually 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 the glass, you can see bubbles of gas, which will be on the walls of the vessel. Along with salts and other substances, water dissolves in itself and gases. First of all, it is nitrogen from the air, as well as oxygen, carbon dioxide, and in some cases still methane and hydrogen sulphide. Moreover, cold water dissolves gases much better than warm water, so that the lower the temperature, the higher the concentration of gases. And conversely, the solubility decreases with increasing temperature.

Sources of dissolved gases in water

But where do all these substances come from in the 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 mud, and hydrogen sulphide is formed as a product of decay of organic residues. As a rule, hydrogen sulphide 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 saturation of water with hydrogen sulphide, there are almost no living organisms other than some bacteria.

Oxygen is also always contained in water. It is a universal oxidizer, therefore partially decomposes hydrogen sulphide, reducing its concentration. But where does oxygen come from? About him, the conversation will be special.

Oxygen

Virtually all living organisms need oxygen. People breathe in the air, which is a mixture of gases, a large part of which is exactly it.

Inhabitants of the aquatic environment also need this substance, so the concentration of oxygen in the water is a very important indicator. Usually it is up to 14 mg / l, when it comes to natural waters, and sometimes even more. In the same fluid that flows from the tap, oxygen is contained much less, and it is easy to explain. Tap water after water intake passes through several stages of purification, and dissolved oxygen is an extremely unstable compound. As a result of gas exchange with the air medium, most of it simply disappears. So where does oxygen come from in the water, if not out of the air?

In fact, this is not entirely true, it also comes from the air, but its share, 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 mineralization. They are not always respected, and life would hardly exist in its present form, if the only way to form this gas in the water environment was to interact with the atmosphere. Fortunately, there are two more sources, from where oxygen is taken in the water. Firstly, dissolved molecules of gas are found in large quantities in snow and rainwater, and secondly - and this is the main source - as a result of photosynthesis carried out by aquatic vegetation and phytoplankton.

By the way, in spite of the fact that the water molecule contains oxygen, living organisms can not extract it from there, of course. Therefore, they have to be satisfied with the dissolved part.

On the importance of algae

Few people in ordinary life think about what we breathe and why the composition of air is exactly what it is. Almost everyone knows that most living organisms breathing air are adapted to this mixture. But if it is a land-air environment, then there are no questions. And where is the oxygen in the water? Like on the ground, there are many plants that, with the help of a process called photosynthesis, consume light and carbon dioxide, secrete O ₂ .

If to be more precise, in recent decades, for one reason or another, humanity has destroyed a large part of the forests. But there is still no question of a global crisis, although the planet's population is constantly growing, and oxygen consumption
It's huge. And great importance in this matter is the algae that inhabit the World Ocean, for the most part it is at their expense that oxygen saturation of the water occurs. Some of their species people and marine life eat, but their number remains sufficient for effective photosynthesis. That's where the oxygen in the water comes from, which means, thanks to the gas exchange with the atmosphere, and in the air. It is the photosynthesis of algae - its main source. By the way, it is due to the processes taking place in the plants that the primary oxygen in the atmosphere was accumulated, and now only the maintenance of its unchanged composition takes place.

The role of dissolved oxygen (PK)

Despite the fact that the respiratory system of aquatic inhabitants is arranged differently than that of the inhabitants of the land-air environment, they need all the same substances. First of all, we are talking about oxygen, which plays an important role in the vital activity of the vast majority of organisms. And if we extract it from the atmosphere, where its share is more or less stable and is about 21%, then the inhabitants of rivers, seas and oceans depend heavily on how much oxygen in the water is contained in their habitat. In addition to fish, oxygen is also needed for plants. However, its products are usually higher than the consumption level, so this should not cause concern.

Normal performance

Due to its significant role in the normal functioning of ecosystems, the level of the RK is often subject to control by biologists and ecologists. After all, everything is connected in nature, breaking the gas balance in one reservoir can cause problems in neighboring ones, if they are connected. As a rule, measurements are taken until noon, during this period the concentration of gas 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.
Reducing the concentration to 2 mg / l and less causes massive death of the inhabitants of the hydrosphere. In fact - from suffocation. A gradual decrease in the indicator may indicate a contamination of the reservoir and may also eventually end in the death of aquatic inhabitants.

In artificial ecosystems

Important importance of good aeration is, for example, in 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 different algae on the bottom. Of course, those who have a similar hobby, first of all, the aesthetics of the ecosystem is interesting, but one should not forget about its stability and some durability.

If we are talking about fish farms, the production of pearls and other specific industries of this type, then in addition to various measures aimed at maintaining a sufficient concentration of dissolved oxygen in the water, it is necessary to regularly measure this index using special samples. When they are fenced, it is extremely important that there is no contact with the air, this can distort the results of the analysis.