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Quality of a River - Water Quality
Sediment: Turbidity (pg 1 of 3)

Turbidity is the property of water that causes light to be scattered or absorbed. Turbidity is caused by the presence of suspended particulate matter in the water column. These particles may be organic forms, such as algae and finely divided plant and animal material, or they may be inorganic forms, such as silts and clays. The visual result of high concentrations of these materials is that water appears muddy, or turbid. A consequence of increased turbidity is reduced water transparency. Transparency is an important measure of stream quality and is commonly assessed in the field with the use of a Secchi disk or transparency tube.

Sediment takes two forms: suspended and deposited. Fine sediment stays more easily in suspension than coarse sand and gravel, which may be moved by bursts of currents, but soon falls to rest on the streambed. For example, fine clay particles from the Blue Earth River in south-central Minnesota are transported all the way from the Minnesota River basin to the Mississippi River basin, where they are finally deposited in quiet backwaters or in Lake Pepin.

Both organic and inorganic particles can block sunlight from the streambed, preventing photosynthesis by aquatic plants. Suspended sediment injures gills of fish and other aquatic organisms, and can impair foraging by sight-feeding fish.


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