Chemical Water Quality

Water contains a variety of chemicals.

Practically all of the naturally occurring elements of the Earth’s crust could probably be found in natural waters. However, some of these substances would be expected to occur only in minute concentrations. In addition to the gaseous components, chemicals are found in varying quantities in natural waters include carbonates, chlorides, sulfates, phosphates and often nitrates. These anions occur in combination with cations such as calcium, sodium, potassium, magnesium and iron to form different ionizable salts.

As a result of availability and high solubility of carbon dioxide in water, carbonates are usually the most abundant salts in fresh waters. Both the quantitative and qualitative aspects of the chemical composition of natural waters are influenced to a high degree by the geochemistry of the watershed. And in the case of lakes, influenced by the form and geology of the basin with respect to inflow and outflow. In general, the inorganic composition of the water of an open lake (that is one with effluents) through which water moves is a reflection of the nature of the influent Waters. The inorganic composition of closed lakes (those lacking significant effluents) is greatly modified by precipitation and concentration of salts as determined by evaporation. Also, lakes near the ocean coast may receive substances from sea spray and moist ocean air.

Chemical Water Quality Parameters

The main differences between lake and stream chemical characteristics usually pertain to relative concentrations, composition, and longitudinal distribution of the substances. Seasonal variation in rainfall and surface runoff along with the geochemical nature of the drainage basin strongly influence the composition of waters of small streams. This combination imparts considerable individuality to streams even within a restricted area or region.

Waters from large streams and rivers, on the other hand, typically exhibit general uniformity of composition, so much so that a quantitative expression of average content becomes meaningful. The mean composition, as percentage proportions of major cations of river water has been given as:

Calcium – 63.5%, Magnesium – 17.4%, Sodium – 15.7%, and Potassium – 3.4%.

Note: that the order of prominence here differs only slightly from that of the North American. In fact, the average composition of rivers is quite similar to that of open lakes, as might be expected.

Next Topics…

Total Dissolved Solids in Water
Electrical Conductivity of Water
pH of Water
Interrelationships of Acidity and Alkalinity in Water
Primary Anions and Cations in Water
Dissolved Gases in Water
Primary Nutrients and Eutrophication
Toxic Constituents in Water
Pesticides in Water
Oil in Water

Go Back to:
Physical Water Quality
Chemical Water Quality
Biological Water Quality
Water Basics 101

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