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Начало › Black Sea › Chemical Balance
Salt content
In the oceanography salt content is what remains after the evaporation at 90° C of 1 kg sea water (filtrated and treated with chloric water in advance), dried at 380° C and hardened at 480° C. After this treatment the bromides turn into chlorides, bicarbonates and carbonates - in oxides, and the original substance burns. There is certain difference between the salt content and its mineralization, due to the transformation of the bicarbonates and carbonates into oxides. Ocean water has lower salt content than the mineralization with approximately 0,08‰ (1969), while the Black Sea water - with about 0,16‰ (1966). The twice bigger difference in the Black Sea water is a result of higher alkalis content (more bicarbonates and carbonates, and in the deep waters there is hydrosulphides). The average annual statistics for a long period show that in the surface waters in the northern region, the minimum salt content is in May, and in the southern region - in June. The maximum in the northern region is usually in December and comparatively rarely in October. In the southern region the maximum are more often in January - December, and in some years - in October and very rarely in September.
Oxygen
The oxygen comes from the atmosphere, when the water becomes colder, and it goes to the air again when the water becomes warmer. It is produced by the photosynthesis of the chlorophyll plant organisms and goes into the atmosphere. It is eliminated in the process of haemsynthesis. Free oxygen is necessary for all organisms, exept non-aerobic bacterium. It is formed (besides by the land plants) mainly in the upper sea layer, and it is used (mostly in breathing and partly in chemical oxidation of some substances) in all layers of the hydrosphere. During the dynamic processes of the water masses the oxygen goes from the upper to the lower layers, viewing the non-considerable diffusion. The regime of the dissolved oxygen in the Bulgarian Black Sea sector - is important for biological researches, but as well as for the chemical structure of the whole sea because of its maximum formation near the west coasts (1978 - 1979).
Carbon dioxide
It is chemical and biological active gas. Dissolved in water it combines partly with water and forms weak acid. At the same time it combines with the carbonates and forms bicarbonates, in which the carbon dioxide is in semi-combined state. This process prevails, that is why there is mostly semi-combined dioxide in water. Carbon dioxide is necessary for the photosynthesis; its quantity in the natural water is practically unlimited, because the free carbon dioxide decreases, the phytolpankton and macrophytes start consuming the semi-combined. Carbon dioxide and the bicarbonates turn into carbonates. The carbon dioxide is eliminates in the breathing of all organisms, including nonaerobic bacterium. Under the photic sea layer (at low vertical circulation) the breathing processes prevail and the quantity of carbon dioxide increases. In the air carbon dioxide is formed by the breathing of the living organisms and the burning and some other processes. There is natural gas exchange between the atmosphere and the hydrosphere, including carbon dioxide.
Sulphuretted hydrogen
It is chemical and biological active gas that forms with water sulphuretted acid. Its dissociation is weak, because it is weak acid. The sulphuretted hydrogen in water is in free and semi-combined state - hydrosulphides. The semi-combined form prevails. There isn"t combined (sulphide) sulphuretted hydrogen in practice. The hydrosulphides, as acid salt of weak acid, hydrolyze through alkaline reaction. They are included in the total alkaline reactions in the deep Black Sea water. The existence of sulphuretted hydrogen under 200 m is found out in 1890. The basic process of sulphuretted hydrogen in the deep Black Sea water is bacterial reduction of sulphates according to the researches. The sulphuretted hydrogen comes into the water as well as a result of decomposition of whites, containing sulphur. In the deep Black Sea water this process is insignificant, but in the bottom slime of the shelf (even in shallow places) it is sometimes considerable. The process is easily noticed when there is heaping of seaweeds and their covering with sand.
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