Hydrochemistry of natural waters

To some extent this is related to the solubility of gases in the natural waters. Many gaseous chemical species are included in biogeochemical cycles in the system of atmosphere-natural waters. When any gas equilibrates with a solvent, the amount of gas which dissolves is proportional to the partial pressure of the gas (see Box 1, Chapter 3). This statement, which is known as Henry s law, can be written mathematically as 

The thermodynamic principles of gas solubility in water are very important. An example of these principles is discussed briefly in Box 1. 

Stream waters can be considered as the composite solutions containing soluble ions and particulate solid matter. The main forms of the occurrence of chemical elements in stream water are  

In analytical practice, the suspended particles are separated by means of membrane filters with various pore diameters. The centrifugation is also of use. Methods for determining the chemical species in waters are described in detail in our previous textbook (Radojevic and Bashkin, 1999). 

In the river waters, the most common soluble species are HC03, S04 and Cl anions accounting, respectively, for48.8%, 10.0% and 5.3% of the sum oftotal soluble compounds. Among the cations, calcium (10.8%), magnesium (2.7%) and potassium (1.2%) are typical. The other elements are present in various trace amounts. 

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