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

particles.
Given that phosphorus may be present in waters in a form of 
several compounds, whose bioavailability is different, it is important 
to determine not only the total phosphorus content, but also the 
phosphorus forms.
Phosphorus compounds have a great importance in eutrophi-
cation processes of water reservoirs and, if the phosphate content 
is  >0.05  mg/l,  with  a  sufficient  quantity  of  nitrogen  compounds, 
an intensive growth and multiplication of algae and other aquatic 
plants can begin in the water body under favourable conditions. The 
phosphate content of the waste water can reach high values, and 
to get rid of that, special technologies are required. When entering 
the bodies of water, phosphorus compounds are assimilated in 
hydrobionts, but, as they decompose, the phosphorus compounds 
largely  accumulate  in  the  sediments.  As  a  result  of  changes  in 
environ mental conditions, the phosphorus accumulated in sediments 
may be released, creating the so-called internal pollution load. 
Silicates  are found in natural waters not only in the form of 
silicic acid anion (HSiO
3
–
, SiO
3
–
), but mostly as polymer compounds 
and colloids. The most significant source of silicates in waters is the 
mineral weathering of silicate. Since the silicate weathering intensity 
is greatly dependent on the ambient temperature, the watercourses 
of warm climates usually have much higher silicon content than 
waters in the temperate zone. Silicon is a biogenic element and it is 
extensively assimilated by aquatic living organisms, mainly diatoms. 
If  the  silicon  content  falls  below  0.5  mg/l,  many  diatom  species 
fail to develop normally, i.e., silicon content in water becomes the 
limiting element in the development of algae. The silicon content in 
lakes  is  typically  around  5  to  10  mg/l,  the  sea  and  ocean  waters 
contain around 0.5 to 3.0 mg/l, but especially soft waters can have 
the content of 50 mg/l SiO
3
–
. Groundwater silicon content can be as 
high as 3000 mg/l. Silicon dioxide (silica) solubility increases with 
rising water temperature and decreasing environ mental pH.

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8. WATER POLLUTION
 173
Iron  can  be  found  in  natural  waters  in  more  than  one  form  – 
ionic form (Fe
2+
, Fe
3+
), iron hydroxide, oxyhydroxide that both 
can create water-suspended particles, and may also be sorbed on 
the solid particle surface in the form of colloidal particles, as well 
as in the form of humic acid and fulvic acid salts. The fate of iron 
compounds in the aquatic environ ment is affected by the oxidation-
reduction processes and the presence of oxygen.
Eutrophication is a plant primary production intensification due 
to rise of nutrient concentration (Table 8.5) in waters.