Quality Assessment: Physical: Turbidity
Turbidity can be measured in two ways. The first involves lowering a special black and white disk called a Secchi disk into the water and determining the maximum depth at which it is visible. The second method of measuring turbidity is a chemical method that involves titrating a turbidity solution into a sample until an equilibrium point is reached. The results of the Secchi disk method are reported in meters. The larger the value, the less turbid the water. The results of the chemical titration method are reported in Nephlometer Turbidity Units (NTU) or Jackson Turbidity Units (JTU), depending on the test kit. The smaller the value obtained from this method, the less turbid the water. Occasional short-term occurrences of high turbidity are common, for example after storm events or when an animal crosses a stream. To determine whether or not there is cause for concern over a high turbidity reading, the measurement should be repeated several times over a twenty-four hour period. In general, a turbidity value of > 40 NTU for at least twenty-four hours indicates a problem. Potential causes for high turbidity include dredging and acid mine drainage.
and Catchment Area / Stream Order /
Forest Canopy / Width,
Depth, and Velocity / Rock Size / Turbidity
/ Total Solids / Temperature
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