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participation of either carbon dioxide (carbonates), sulfates or
water organic substances. Rock weathering is one of the key factors
significantly affecting the mineral composition of natural waters.
Today, for example, the aluminum content levels in natural waters
are increased by intense weathering of aluminosilicate under the
impact of acid rain.
Igneous rocks are formed of magma, as it cools and hardens
in the depths of the Earth (intrusive magmatic rock) or flowing
out to the surface of the Earth in the form of volcanic lava
(effusive rock). Metamorphic rocks are formed from magmatic
Minerals are naturally
occurring inorganic
compounds, which have
a crystalline structure
and a particular chemical
composition. Rocks are
stable geological bodies
that are composed of
mineral aggregates.
The rocks make up the
Earth’s crust. According
to the origin, the
rocks are classified as
magmatic, sedimentary
or metamorphic.
8. WATER POLLUTION
167
rocks and sedimentary rocks, as well as older metamorphic rocks
in metamorphism processes. Metamorphism is a set of geological
and geochemical processes, in which under the exposure of high
temperature, pressure and chemically active solutions and gases,
the changes in rock mineralogical composition and structure take
place. The major sedimentary rocks are clay, conglomerate rocks
(sandstone, breccia, conglomerates) and carbonate rocks. Clayey
rocks predominantly consist of silicates and aluminosilicates, but for
their composition potassium, magnesium and iron compounds are of
great importance.
Carbonate rocks consist of magnesium and calcium carbonates.
Water composition is formed as minerals and rocks dissolve in
aquatic environ ment, or as a result of their chemical transformation.
The main minerals whose weathering affects the composition of
natural waters are the rock salt (NaCl), gypsum (CaSO
4
·
2H
2
O),
calcite (CaCO
3
), dolomite (CaMg(CO
3
)
2
), siderite (FeCO
3
), goethite
(FeOOH), quartz (SiO
2
) and aluminosilicates.
There is a distinction between complete and partial dissolution
of the rocks. As a result of complete dissolution a mineral is fully
dissolved, forming only water-soluble substances. Partial dissolution
results in water-soluble substances and a new mineral. The main
groups of substances affecting mineral dissolution, are acids
dissolved in water (carbonic acid, sulfuric acid, hydrogen sulphide,
organic acids, humic acids), gases. Mineral stability (resistance to
weathering) greatly differs. This means that in the soil, which is a
mixture of several minerals, some of these will dissolve significantly
faster than the others. Based on the way they affect the natural
water content, the most important of mineral weathering processes
is the silicate and carbonate weathering.
The intensity of each of these processes is determined by the
soil type and composition. Soils rich in organic matter (humus),
especially in swampy areas, first of all enrich the waters with humic
substances. Black earth, but especially clay (loam, clay, loess) soils
promote ion composition changes in natural waters. It should be
noted that the interaction of waters with the mineral substances
existing in soil takes place with an active participation of CO
2
.
The biological factors also influence the formation of
water composition. It is particularly associated with activity of
microorganisms. A set of biological factors determines the biological-
biogenic transformation of natural waters, which, in turn, affects the
microelements and determines the content of organic substances.
Microorganisms are found even in groundwater up to 1000 m
deep, and can grow at temperatures from 0 to 90 °C. The presence
of microorganisms fundamentally affects the gas regime and
determines the synthesis, dissolution and transformation of organic
The composition of
natural waters, is very
significantly affected
by the leaching of
substances from the soil.
This effect can manifest
itself in two ways:
1. by changing the che‑
mical composition of
water that percolates
through the soil;
2. by impacting the
groundwater chemical
composition.
168
ENVIRONMENT, POLLUTION, DEVELOPMENT: THE CASE OF UZBEKISTAN
substances. The presence of microorganisms is the main determinant
in the degradation processes of environ mental pollutants and toxic
substances. Water quality and composition is actively influenced by
plants and animals.
The final stage in creating the water quality is completed by
various water mixing processes, which may change the composition
of water, for example, in case of poorly soluble salt formation. When
the waters of various content mix, deposition of the dissolved or
suspended substances is typical.
Since the water solubility of many substances is very high,
the content of different dissolved substances in natural waters can
vary significantly – from a few milligrams per litre up to tens or
hundreds of grams per litre. Depending on the concentration of
dissolved substances and ions, they are classified as dominant,
macro components and microelements (Table 8.2).
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