Water chemistry includes measures of various elements and molecules dissolved or suspended in water. Some "chemical" measures are actually physical measures that indicate the presence of chemical features of water. For instance, conductivity is a physical measure (the ability of water to conduct an electrical current) that indicates the presence of dissolved chemicals in water. When salt, such as sodium chloride (NaCl, table salt) dissolves in water, it forms ions (Na+ and Cl-) that allow a current of electricity to pass through the water.
Chemical measures commonly used in water quality field surveys reveal some form of pollution, which indicates an imbalance within the stream ecosystem. For instance, pH identifies acid/base balance of water. Low pH values are particularly useful for detecting acid mine drainage. However, since some streams are naturally acidic, a low pH does not necessarily indicate acid mine drainage. In other systems, pH may not detect acid mine drainage because of the natural buffering of the stream. In Wheeling Creek, for instance, low pH is sometimes detected in small tributary streams that drain abandoned mine lands, but pH in the mainstream below the mine site may be normal because of its level of alkalinity . Alkalinity is a measure of the water's ability to resist changes in pH. It results from dissolution of calcium carbonate (CaCO3) from limestone bedrock, which is eroded during the natural process of weathering in the Wheeling Creek watershed.
Some chemical indicators are specific to particular forms of pollution, but most indicate only that something is out of balance. For instance, low dissolved oxygen often results from input of raw sewage, but also result from oxygen consumption during reactions that generate acid mine drainage.
In this study pH,
conductivity, dissolved oxygen, and temperature were measured with a water quality sonde
and data logger. Alkalinity and hardness were measured with
direct reading titration kits. Kenneth E. Rastall using water quality meter. Photo: Courtesy of Dr. Ben Stout
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