Does cloudy water hold more dissolved oxygen or less? Most people assume murky water means poor quality. But turbidity (cloudiness from suspended particles) may have a surprising link to dissolved oxygen.
You collect water samples from different spots in a river. For each sample you measure turbidity with a turbidimeter. You measure dissolved oxygen using a chemical titration method. Counting drops of sodium thiosulfate until the yellow color clears tells you the dissolved oxygen level.
The results were unexpected. Samples with higher turbidity actually had higher dissolved oxygen. Samples with lower turbidity had lower dissolved oxygen.
Hypothesis
The hypothesis is that the more turbidity levels in water increase, the more dissolved oxygen levels decrease.
Dissolved oxygen is the oxygen gas mixed into water that aquatic animals depend on. Measuring it reveals whether a body of water can support life. Most people assume murky water is always lower in quality — but this river study found something unexpected. Water samples from different spots showed that higher turbidity actually corresponded to higher dissolved oxygen levels. Counting drops of sodium thiosulfate until the yellow color cleared gave the dissolved oxygen readings, while a turbidimeter measured cloudiness. The results challenged the assumption: clearer water had lower dissolved oxygen, not higher.
Cloudy water and dissolved oxygen might seem unrelated, but testing them together reveals something unexpected. You collect samples from different spots in a river, measure turbidity with a turbidimeter, then determine dissolved oxygen by counting drops of sodium thiosulfate until the yellow color clears. Samples with higher turbidity actually had higher dissolved oxygen — the opposite of what most people would predict, and a result worth further investigation.
Method & Materials
You will find an area of water to test, put a jar beneath the river surface, add dissolved oxygen pillows to the sample, and measure the turbidity levels with a turbidometer.
You will need a turbidometer, bottle with stopper, dissolved oxygen pillows, sodium thiosulfate, protective gloves, nail clippers, boots/hipwaiters, testing tube, and 10 quart jars.
Eureka Crate — engineering & invention kits for ages 12+ — monthly projects that build real-world skills. (Affiliate link)
The results of the experiment indicate that higher turbidity levels actually increase the level of dissolved oxygen in water, which is contrary to the hypothesis. This experiment could lead to further exploration of how turbidity affects photosynthesis.
Why do this project?
This science project is interesting because it explores the relationship between two important factors in water quality, turbidity and dissolved oxygen.
Also Consider
Experiment variations to consider include testing different types of water, such as salt water or fresh water, or testing different levels of turbidity.
Full project details
Additional information and source material for this project are available below.
