Māris kļaviņŠ, azamat azizov, JĀnis zaļoksnis environment, pollution, development: the case of uzbekistan

Figure 4.20. 
Changes in 
carbon dioxide emission 
amounts over the last 
centuries

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68 
ENVIRONMENT, POLLUTION, DEVELOPMENT:  THE CASE OF UZBEKISTAN
Atmosphere 750
Vegetation 610
Soils
1580
Marine biota 3
Dissolved organic 
carbon <700
Sediments 150
Deep ocean
38 100
Ocean surface 1020
Rivers
Energy production,
motor transport, industry
4000
Coal, oil, 
carbonate rocks
5.5
CO
2
0.5
6
4
6
0.2
91.6
100
40
50
90
92
60
60
1.6
121.3
 4.2.3.  Nitrogen biogeochemical cycle
Nitrogen makes 76% of the atmo sphere’s mass, and it is one 
of  the  most  important  chemical  elements  in  proteins  and  DNA; 
there fore, it is one of the elements necessary for the existence of 
living  organisms.  At  the  same  time,  the  concentration  of  nitrogen 
compounds in the litho sphere and hydrosphere is quite low. Unlike 
oxygen, nitrogen is inert, and most living organisms cannot utilise it 
directly, because the bonds between atoms in nitrogen molecules are 
very stable. Processes in the nitrogen cycle ensure the bonding of 
atmo spheric nitrogen (N
2
) into such compounds that can be utilised 
by living organisms.
In the environment, nitrogen compounds are found as 
nitrogen(I) oxide (N
2
O), nitrogen(II) oxide (NO), nitrogen(IV) oxide 
(NO
2
), nitric acid (HNO
3
), ammonia (NH
3
) and ammonia salts. 
Other nitrogen compounds either form intermediate products in 
various reactions, or are unstable and decompose fast. Nitrogen 
compounds are interrelated, and they can be converted into one 
another (Figure 4.22). Reactions caused by micro-organisms play an 
important part in the nitrogen cycle, for these micro-organisms in 
the hydrosphere and lithosphere are involved in the conversion of 
most nitrogen compounds. In other words, they catalyse the synthesis 
of nitrogen compounds necessary for the existence of the biosphere’s 
living organisms. It should be noted that only a small part of nitrogen 
compounds become involved in the nitrogen cycle, because nitrogen