Quality Assessment: Chemical
Assessment of water quality by its chemistry includes measures of many elements and molecules dissolved or suspended in the water. Chemical measures can be used to directly detect pollutants such as lead or mercury. Chemical measures can also be used to detect imbalances within the ecosystem. Such imbalances may indicate the presence of certain pollutants. For example, elevated acidity levels may indicate the presence of acid mine drainage.
Commonly measured chemical parameters include pH, alkalinit , hardness, nitrates, nitrites and ammonia, ortho- and total phosphates, and dissolved oxygen and biochemical oxygen demand. The presence of fecal coliform, a bacteria, is also determined using a chemical test. This microscopic organism is too small to detect during the biological assessment of macroinvertebrate populations. In addition, some "chemical" measurements actually indicate the physical presence of pollutants in water. These include measurements such as conductivity and density.
Measurements of these chemical parameters of water quality can be made one at a time using low-tech field titration kits such as Hach Kits (see left). However, several of these parameters may be measured at once using high-tech equipment such as the YSI 3800 Water Quality Logger (see above). Photo: Students using Hach Kits to measure several chemical parameters of stream water quality one at a time. Photo courtesy of Dr. Ken Rastall.
/ Alkalinity / Hardness
/ Nitrates. Nitrites, and Ammonia / Ortho-
and Total Phosphate / Dissolved Oxygen and
Biochemical Oxygen Demand / Fecal Coliform
/ Conductivity and Density
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