|Methods for Monitoring
This page addresses methods and tools to monitor and assess the quality of water resources.
Common Biological Measures
Common Chemical Measures
The level of nitrates in a body of water is another chemical measure of water quality. Nitrogen exists in water in numerous forms, two of which are nitrate (NO3) and nitrite (NO2). Of these two forms, nitrate is usually the most important. Nitrate is an essential nutrient for growth of algae and other aquatic plants, and can be present at high levels due to a variety of sources. Nitrate is very difficult to measure directly. A common procedure is to first measure the level of nitrite and then reduce the nitrate to nitrite and measure the combined nitrite concentration. Subtracting the original nitrite level from the combined nitrite concentration will give you the nitrate level. Nitrate measurements are reported as nitrate nitrogen (mg/L). Nitrite measurements are reported as nitrite nitrogen (mg/L).
Some chemical indicators are specific to particular forms of pollution. For instance, low dissolved oxygen often results from either the presence of raw sewage or acid mine drainage.
Other "chemical" measures are actually physical measurements that indicate the presence of chemicals in the water. For instance, conductivity--the ability to conduct an electrical current--is a physical measurement that indicates the presence of chemical ions in the water sample. For example, when table salt (NaCl, sodium chloride) dissolves in water, it forms ions (Na+ and Cl-) that allow a current of electricity to pass through the water. Water density is another physical measurement that indirectly indicates the presence of chemicals. The density of water is related to salt content (salinity) and water temperature. The salinity of a body of water is one of the main factors determining what organisms will be found there.
Common Physical Measures
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