Ammonium toxicity increases with increasing pH of the medium .
CaCO3 + CO2 + H2O Ca (HCO3) 2
HSiO3- + CO2 + H2O H2SiO3 + HCO3-
The reduction of carbon dioxide in water also occurs as a result of its release into the atmosphere.
The concentration of carbon dioxide in natural waters ranges from a few tenths of a share to 3-4 mg / dm3, occasionally reaching 10-20 mg / dm3.
Usually in spring and summer the content of carbon dioxide in the reservoir decreases, and at the end of winter reaches a maximum. Carbon dioxide is extremely important for plant organisms (as a source of carbon). At the same time, elevated concentrations of CO2 inhibit the development of animal organisms. At high concentrations of CO2, water becomes aggressive against metals and concrete as a result of the formation of soluble hydrocarbons, which disrupt the structure of these materials , , .
The main source of hydrocarbonate and carbonate ions in surface waters are the processes of chemical weathering and dissolution of carbonate rocks such as limestone, marl, dolomite, for example:
CaCO3 + CO2 + H2O Ca2 + + 2HCO3-
MgCO3 + CO2 + H2O Mg2 + + 2HCO3-
Some of the bicarbonate ions come with precipitation and groundwater. Hydrocarbonate and carbonate ions are carried out in reservoirs with sewage of the enterprises of the chemical, silicate, soda industry, etc.
As the accumulation of hydrocarbonate and especially carbonate ions, the latter can precipitate:
Ca (HCO3) 2 => CaCO3 + H2O + CO2
Ca2 + + CO32- => CaCO3
In river waters the content of hydrocarbonate and carbonate ions varies from 30 to 400 mg HCO3 – / dm3, in lakes – from 1 to 500 mg HCO3- / dm3, in sea water – from 100 to 200 mg / dm3, in atmospheric precipitation – from 30 up to 100 mg / dm3, in groundwater – from 150 to 300 mg / dm3, in groundwater – from 150 to 900 mg / dm3.
The sum of mineral and organic nitrogen in natural waters. Nitrogen-containing compounds are in surface water in a dissolved, colloidal and suspended state and can be transferred from one state to another under the influence of many physicochemical and biochemical factors.
The average concentration of total nitrogen in natural waters varies considerably and depends on the trophic nature of the water body: for oligotrophic varies usually within 0.3-0. 7 mg / dm3, for mesotrophic – 0.7-1. 3 mg / dm3, for eutrophic – 0.8-2. 0 mg / dm3 .
The amount of mineral nitrogen
The sum of ammonium, nitrate and nitrite nitrogen.
An increase in the concentration of ammonium ions and nitrites usually indicates recent contamination, while an increase in nitrate content indicates previous contamination. All forms of nitrogen, including gaseous, are capable of mutual transformations.
In natural water, ammonia is formed by the decomposition of organic matter containing nitrogen. Well soluble in water from ammonium hydroxide compounds.
The MPC of ammonia is 40 mg / dm3, the MPC of 0.08 mg / dm3 is the limiting sign of harmfulness – toxicological .
The content of ammonium ions in natural waters varies in the range from 10 to 200 μg / l in terms of nitrogen. The presence of ammonium ions in unpolluted surface waters is mainly associated with the processes of biochemical degradation of protein substances, deamination of amino acids, and decomposition of urea by urease. The main sources of ammonium ions in water bodies are livestock farms, domestic wastewater, surface runoff from farmland with the use of ammonium fertilizers, as well as wastewater from food, coke, forest chemical and chemical industries. In the effluents of industrial enterprises it contains up to 1 mg / dm3 of ammonium, in domestic effluents – 2-7 mg / dm3; with domestic wastewater in the sewer system daily receives up to 10 g of ammonium nitrogen (per capita) .
During the transition from oligotrophic to meso- and eutrophic reservoirs, both the absolute concentration of ammonium ions and their share in the total balance of bound nitrogen increase.
The maximum permissible concentration in the water of drinking water and cultural water use (MPC) is set at 2 mg / dm3 for nitrogen or 2.6 mg / dm3 in the form of NH4 + ion
The presence of ammonium in concentrations of the order of 1 mg / dm3 reduces the ability of fish hemoglobin to bind oxygen. Signs of intoxication – disturbances, convulsions, the fish throws itself on the water and jumps to the surface. The mechanism of toxic action – disorders of the central nervous system, lesions of the gill epithelium, hemolysis (rupture) of erythrocytes. Ammonium toxicity increases with increasing pH of the medium .
The increased concentration of ammonium ions can be used as an indicator that reflects the deterioration of the sanitary condition of the water body, the process of pollution of surface and groundwater, especially domestic and agricultural effluents.
The presence of nitrate ions in natural waters is associated with:
internal processes in the reservoir – nitrification of ammonium ions with the participation of oxygen under the action of nitrifying bacteria; precipitation, which absorbs oxides of nitrogen generated by atmospheric electric discharges (the concentration of nitrates in precipitation reaches 0.9 – 1 mg; industrial and domestic wastewater, especially after biological treatment, when the concentration reaches 50 mg / dm3; runoff from agricultural lands and with runoff of water from irrigated fields on which nitrogen fertilizers are applied.
The main processes aimed at reducing the concentration of nitrates are their consumption by denitrifying bacteria and phytoplankton, which in the absence of oxygen use nitrate oxygen to oxidize organic matter.
In surface waters, nitrates are in dissolved form. The concentration of nitrates in surface waters is subject to seasonal fluctuations: minimal in the growing season, it increases in autumn and reaches a maximum in winter, when the minimum consumption of nitrogen is the decomposition of organic matter and the transition of nitrogen from organic to mineral forms. The amplitude of seasonal fluctuations can be one of the indicators of eutrophication of a water body. , .
In unpolluted surface waters, the concentration of nitrate ions does not exceed the size of tens of micrograms per liter (in terms of nitrogen). With increasing eutrophication, the absolute concentration of nitrate nitrogen and its share in the amount of mineral nitrogen increases, reaching n. 10-1 mg / dm3. In unpolluted groundwater, the content of nitrate ions is usually expressed in hundredths, tenths of a milligram and less often in units of milligrams per liter. Groundwater aquifers are more prone to nitrate pollution than surface water bodies (because there is no consumer of nitrates) .
Values of maximum permissible concentrations of nitrates for vegetables and fruits, mg / kg 
With long-term use of drinking water and foods containing significant amounts of nitrates (from 25 to 100 mg / dm3 for nitrogen), the concentration of methemoglobin in the blood increases sharply. Methemoglobination is extremely severe in infants (primarily, artificially fed milk formulas prepared in water with high – about 200 mg / dm3 – nitrate content) and in people suffering from cardiovascular disease. Groundwater that feeds wells is especially dangerous, as nitrates are partially consumed by aquatic plants in open water.
The presence of ammonium nitrate in concentrations of the order of 2 mg / dm3 does not cause disruption of biochemical processes in the reservoir; the maximum concentration of this substance that does not affect the sanitary regime of the reservoir, 10 mg / dm3. Concentrations of harmful nitrogen compounds (primarily ammonium) for various fish species are in the order of hundreds of milligrams .
Along with the described effects of impact, the fact that nitrogen is one of the primary nutrients (necessary for life) plays a significant role. This is due to the use of nitrogen compounds as fertilizers, but, on the other hand, it is associated with the contribution of nitrogen removed from agricultural lands in the development of eutrophication (uncontrolled growth of biomass) of water bodies. So, from one hectare of irrigated lands 8-10 kilograms of nitrogen are taken out in water systems.
The maximum permissible concentration in water of reservoirs (MPCv) is set at 10 mg / l for nitrogen or 45 mg / l in the form of NO3- ion (limiting indicator of harmfulness – sanitary-toxicological). The requirements for the composition of drinking water also specify a standard that corresponds to 10 mg / dm3 for nitrogen or 45 mg / dm3 in the form of the ion NO3- (identical to the US standard for drinking water).
Represent an intermediate stage in a chain of bacterial processes of oxidation of ammonium to nitrates (nitrification – only in aerobic conditions) and, on the contrary, reduction of nitrates to nitrogen and ammonia (denitrification – at lack of oxygen). Such redox reactions are characteristic of aeration stations, water supply systems and natural waters themselves. In addition, nitrites are used as corrosion inhibitors in the process of water treatment of process water and therefore can get into the drinking water supply system. The use of nitrites for food preservation is also widely known.
In surface waters, nitrites are in dissolved form. Small concentrations of nitric acid (HNO2) (not dissociated into ions) may be present in acidic waters. The increased content of nitrites indicates the intensification of the decomposition of organic matter in the conditions of slower oxidation of NO2- to NO3-, which indicates the pollution of the water body, ie is an important sanitary indicator .
The concentration of nitrites in surface waters is hundreds (sometimes even thousands) of milligrams per 1 dm3; in groundwater, the concentration of nitrites is usually higher, especially in the upper aquifers (hundredths, tenths of a milligram in 1 dm3).
Seasonal fluctuations of nitrites are characterized by their absence in winter and appearance in spring during the decomposition of inanimate organic matter.