Overview and Background

Turbidity is a description of how cloudy water is. It's opposite would be clarity. The cloudiness can be caused from organic (phytoplankton) or inorganic (silt) material suspended in the water. Turbidity is an important indicator of water quality. The suspended particles can increase water temperatures, interfere with photosynthesis, clog gills, provide a place for harmful microorganisms to proliferate and help suspend some toxic substances in the water column.

These days turbidity is often measured with a digital instrument that quantifies how much a beam (or two) of light is scattered by particles suspended in the water. These instruments will give you a number in Nephelometric Turbidity Units (NTU's). A simpler method is to lower a secchi disk (a circle divided into opposing white and black quadrants) into a body of water until it is no longer visible. This distance is then measured for comparison with other locations. A secchi disk can also be incorporated into a clear tube and a water sample slowly released from the tube until the disk becomes visible. The depth of water left in the tube is then measured for comparison with other locations. These turbidity tubes are useful when you want to sample turbidity from shore. Turbidity tubes are a great way for students to explore what turbidity is. Good quality turbidity tubes can be a bit expensive though. So why not make some....

This Thing is a small portable version of a turbidity tube (though you can make yours as big as you like). You need to paint two opposing quadrants white on the inside of the base to make your secchi disk. To convert your readings to NTU's use the chart found at:

http://extension.usu.edu/utahwaterwatch/monitoring/field-instructions/turbidity/turbiditytube/turbiditytubeconversionchart

Materials:

3D printed parts (I printed mine at 0.4mm as fast as my Afinia H480 would go and the parts fit perfectly inside the clear tube).
Clear Fluorescent tube cover (available in most hardware stores)
Silicone
Permanent marker
White waterproof paint

To build you will need to follow these steps:

Print the parts
Cut the tube to desired length (I use 30 or 60 centimeters).
Paint two opposing quadrants on the inside of the base white.
Connect everything (perhaps use a bit of silicone when attaching the base to prevent leaks)
Add graduations (either by hand or with a sticker). This website has a nice selection of rulers you can print and attached to your tube. https://printable-ruler.net/all-rulers/

To use:

Place finger or thumb over hole in base
Dip tube into aquatic system to be surveyed, fill to top
Hold vertical and look through tube from top to bottom
Remove your finger or thumb from hole and slowly let water out until you can see secchi disk at bottom.
Recover hole.
Measure how much water is left in tube.

Lesson Plan and Activity

If your a teacher and want to use these with a class consider comparing the turbidity of two or three nearby water bodies and have the students attempt to explain any differences based on their observations of each system. Observing changes through the fall or spring are also fun and interesting for students to chart and explain.

Turbidity Tube