Decreased water clarity in a waterway can be a concern
WAV monitors use a transparency tube to assess the clarity of the water. The tube allows monitors to estimate stream water quality based on visual assessment of the amount of light that is scattered and absorbed by the particles that are suspended in the water sample. Every stream and river has a natural level of clarity that organisms which inhabit the system can tolerate. It is often changes in clarity, particularly in frequency or longevity of cloudiness of the water, that are cause for concern. Assessment of clarity using transparency tubes is useful because potential runoff problems might be noted by assessing it on a regular basis, specifically before, during and immediately after rain storms.
Turbidity can be measured in the laboratory with a meter, called a nephelometer, which measures the amount of light scattered by particles in the water in nephelometric turbidity units (NTUs). The tubes that WAV monitors use have been calibrated so that transparency values can be converted to units that approximate NTUs.
Some WAV monitors' transparency tubes are made using fluorescent light bulb sheaths and other materials that can be purchased locally (others are made with lake coring tubing or are made commercially). Directions for how to create your own transparency tube >>
The basics about turbidity:
Increased turbidity can increase the temperature of the water because particles suspended in the water absorb the sun's heat more than pure water.
Increased turbidity will limit the amount of light that can enter a waterbody, and may therefore limit plant photosynthesis, and thus, oxygen production. This means that the water may have less ability to support aquatic life with increased turbidity. Increased turbidity beyond background levels can irritate gills in fish and macroinvertebrates, thus negatively affecting their growth and/or survival. Turbid conditions can make it difficult for sight-feeding predators, such as bass, pike, and trout to find their food in aquatic systems. Other fish, such as carp, which do not depend on sight to feed, are better able to survive in turbid conditions. Habitat, particularly substrate which may provide hiding spots or nesting sites, can also be negatively affected by sedimentation.
Things that affect water clarity:
There are both natural and anthropogenic sources which affect the clarity of the water.
|Natural Sources||Anthropogenic Sources|
|Tannic acids that are leached from tree leaves/needles||Sediments in runoff from construction sites, farm fields, streets|
|Algae that grow with nourishment from nutrients entering the stream through leaf decomposition or other naturally occurring decomposition processes||Algae that grow in the stream due to increased nutrients from lawn or farm fertilizers, sewage from treatment plant discharges, or improperly functioning septic systems|
Can you think of other sources that
might affect water clarity?
Data Sheet (88 K pdf)
Methods (1.10MB pdf)
Transparency Training Video approximate run time 5:20
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