Turbidity Trouble
Measure the cloudiness of water samples to determine correlation between weather events and local water quality.
PASPORT Turbidity Sensor
(PS-2122)
Lab Summary
Students will measure the turbidity (cloudiness) of water samples from locations near their campus. By sampling on various days and observing local weather conditions, students will investigate whether there is any correlation between weather events and local water quality.
Imagine being in a boat on a sunny day, heading out onto a lake. The clearer the water, the more sunlight can penetrate the surface, and the deeper you can see. If the water is cloudy because of solid particles floating in it, less light can pass through it, and an object submerged beneath the surface will soon be invisible from the boat. Turbidity is a measure of this cloudiness. It is measured in units called NTU's (nephelometric turbidity units), based on how light is scattered by the particles suspended in the water.
There are three major types of particles that contribute to turbidity. The first is algae, which grows in all kinds of lakes and streams. Second, dead organic matter (from algae, plants, bacteria, fungi, etc.) also gets washed into lakes, streams and oceans and adds more particles to the water. Third, silt and sediment from shoreline erosion and from disturbance of the riverbed or lakebed also becomes suspended in the water, making it cloudy.
When less sunlight penetrates water, aquatic plant growth is limited. Fewer aquatic plants mean less photosynthesis and therefore less oxygen in the water. Reduced oxygen affects fish and other organisms that feed on plants and rely upon the oxygen dissolved in the water. When water is cloudy, the particulate matter absorbs heat from the sun and increases the water temperature. This also decreases the amount of oxygen that is in the water and can adversely affect aquatic life.
Hypothesize: Plan where you will obtain water samples near your campus. How clear or cloudy do you expect each water sample to be? If the weather changes in the next few days, and you measure the turbidity of samples from the same locations later on, how might the turbidity change?
Published: March 2003
Downloads
- Turbidity Trouble (21 KB, .zip)
Includes experiment setup and procedures
Here's What You Need
U.S. Educator prices shown.
Probeware
PASPORT Turbidity Sensor (PS-2122) - $125
The Turbidity Sensor measures the turbidity level (cloudiness) of water in nephelometric turbidity units (NTU).
Xplorer GLX (PS-2002) - $329
The Xplorer GLX is a data collection, graphing, and analysis tool designed for science students and educators.
Other Materials
- Sampling containers -- plastic flasks or beakers, or jars with lids
- Sample cuvettes (come with the Turbidity Sensor)
- Water samples (approx. 6 mL each) from various locations: pond, puddle, stream, collected rainwater, drinking faucets, etc.
- Distilled water -- control