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Acid Mine Drainage: Hardness
Image of two people looking at some baserock.  This image links to a more detailed image.Water hardness is the total concentration of cations, specifically calcium (Ca2+), magnesium (Mg2+), iron (Fe2+) and manganese (Mn2+) in water. Photo: Courtesy of Kenneth E. Rastall

A stream's hardness reflects the geology of the catchment area and sometimes provides a measure of the influence of human activity in a watershed. For instance, acid mine drainage often releases iron (Fe2+) into a stream, resulting in extraordinarily high hardness readings. For this reason, hardness is a useful water quality indicator. For the most part, however, hardness is a measure of the calcium and magnesium that enters the stream through the weathering of rock.

In the Wheeling Creek watershed, the bedrock is mostly limestone. Limestone is calcium carbonate, or CaCO3. When limestone weathers, it dissolves into calcium (Ca2+) and carbonate (CO32-). Calcium is an important nutrient used by plants and animals as it moves downstream. Carbonate enters the carbonate buffering system described under alkalinity.

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