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

Figure 8.8. 
Eutrophication effects in 
the waters
Figure 8.9. 
Eutrophic 
waters with heavy algal 
blooms during summer 
season

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176 
ENVIRONMENT, POLLUTION, DEVELOPMENT:  THE CASE OF UZBEKISTAN
 
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deep-water  horizons  accumulate  hydrogen  sulfide,  carbon 
dioxide, dissolved iron and / or manganese;
 
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as a result of algae sedimentation and decomposition, the 
intensive formation of methane takes place, sediment-bound 
nitrogen and phosphorus compounds are released in water;
 
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development of undergrowth and filamentous algae;
 
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if the water turbidity is increased, the transparency falls 
below 0.3 m, and rapidly (even within one year) underwater 
vegetation disappears;
 
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suffocation  of  fish  under  the  ice  or  as  a  result  of  intense 
photosynthesis in summer, which determines the pH increase 
and promotes intoxication.
The processes in nature, which are characterized by these 
features, are irreversible.
Water contamination with organic substances always has a very 
complex character. Organic pollutants are able to actively interact 
with  a  variety  of  naturally-occurring  substance  groups.  Another 
special feature characteristic of this group of substances is that they 
are strongly affected (transformed, destroyed) by a variety of living 
organisms, primarily bacteria, fungi, yeasts.
The complex chemical content of the organic environ mental 
pollutants  usually  makes  it  difficult  to  analyse  the  waste  water 
containing these substances. Typically, such waste water is analysed 
by looking at the organic substances at a certain aggregate amount, 
which is able to consume oxygen, according to COD or BOD values.
On the other hand, the water-dissolved oxygen content might 
be  considered  as  a  different  criterion,  whose  content  values  show 
the  inflow  of  biodegradable  organic  substances  into  the  waters. 
Figure  8.10.  illustrates  the  general  concepts,  which  characterize 
the changes in the composition of waters in case of the waste water 
discharge. 
River flow
Pollution
source
BOD
Oxygen saturation
Oxygen
The amount of organic 
material dissolved in 
waters is characterized 
by determining the 
amount of oxygen that 
is consumed by either 
chemical oxidation of 
organic matter (chemical 
oxygen demand – COD), 
or as the aquatic living 
organisms consuming 
dissolved substances 
as a result of their life 
processes (biological 
oxygen demand – BOD).