Youth water quality tests – Part 5 – Turbidity

Teach students about science by playing in the river! You can learn about the pollution in the river by studying the turbidity.

These articles discuss the water quality tests conducted as part of the international program called Global Rivers Environmental Education Network (GREEN). GREEN began in the spring of 1984 with a group of concerned students at a high school located along the polluted Huron River in Ann Arbor, Mich.  Their teacher contacted Dr. William Stapp at the University of Michigan, and together they developed this comprehensive educational program. This is the fifth article in a series by Michigan State University Extension about testing water quality with students.  By conducting some simple tests, students can learn about how clean or polluted nearby streams are.  By doing further investigation, the students can identify the problem and help to improve the river.

Young people can partner with local schools, watershed groups, lake associations, drain commissioner offices, conservation districts, nature centers or other groups to conduct these tests. 

The background
Turbidity is a measure how “mucky” water is; the greater the turbidity the murkier the water.  The amount of dirt, algae and other things floating in the water will reduce the penetration of light into the water.  As light decreases, so does photosynthesis by plants.  When plants aren’t going through photosynthesis, they are not making oxygen.  High turbidity can also make it difficult for predators that use their sight as a way to capture their prey.  A rain event leading to high turbidity can lead to bad fishing until the water clears back up again.  High turbidity may be caused by soil erosion, waste discharge, runoff, abundant bottom feeders (such as carp) that stir up the bottom or algal growth. Sediment in the water also can carry phosphorus and other contaminants.  High turbidity can also mean there is a lot of stream erosion going on and unstable river banks.

The Test
In lakes, ponds and slow moving water, turbidity can be measured best by a Secchi disk.  A Secchi disk is a circle divided into alternating white and black quarters attached to a line.  Directions for making a Secchi disk are available from the MiCorps website. You lower the disk into the water until it cannot be seen and make a note of the distance.  Then raise the disk slowly until you can just see it and write down that distance.  Average the two measurements, and that is your Secchi disk reading.

In fast moving water, turbidity cannot be measured using a Secchi disk, because the flow is too great.  In those cases, turbidity must be measured with a test kit or meter.  These can be purchased online from several companies.

Looking at the data and what kids can do to make it better
Turbidity is caused by sediment suspended in the water.  This sediment usually runs off from areas that do not have plants growing.   Students can look around their school and community and look for areas of bare soil. Planting those areas and maintaining them can be an excellent way to beautify their community as well as prevent pollution.  If there is a stream near their school, working with local conservation districts to put in buffer strips can help as well.

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