Water clarity
Water clarity is a measure of underwater visibility in rivers and streams. It indicates how much fine sediment, algae and other particles are in the water column.
Reduced clarity can be harmful to the animals living in or near the water. It also restricts sunlight from getting to the plants that need sunlight to photosynthesise.
Measure water clarity by using a clarity tube or periscope viewer.
These Rivers and Us resources are in a downloadable PDF format. Use them as a guide to the scientific methodology for measuring water quality. They also has discussion and reflection questions.
Transcript
VOICEOVER
Water clarity – or turbidity – is a measure of underwater visibility in rivers and streams. This measurement indicates how much fine sediment, algae and other particles are in the water column.
Reduced clarity means under water there is reduced visibility – this can be harmful to the animals living in or near the water. It also restricts sunlight from getting through the water column to the plants under water that need sunlight to photosynthesise.
Measuring turbidity or water clarity can be done using a water clarity tube or black disc and periscope viewer. It is important to always use the same testing protocol to ensure your data is robust and can be used to compare over time.
LYN ROGERS
One of the things that we’re looking at when we’re looking at water quality is to see how clear the water is. This is a piece of equipment that scientists use for that, and it’s called a clarity tube. We’re going to be having real water inside, and one of us will be looking down and the other one of us will be moving this until we can’t see it any more. Then that measurement there will tell us whether the water is really clear or really cloudy. If we only get to here, it means there was so much sediment or dirt in the water that stopped us seeing that pretty quickly.
VOICEOVER
Fill the clarity tube with water collected from the main stream flow.
Place the magnet in and out of the tube and put the black cap on so it is watertight.
Hold the tube horizontally and place your eye close to the clear end of the tube.
Start with the magnet close to you and then slowly move it away from you until you cannot see it. Record this measurement.
Next, pull it back very carefully towards you until it just reappears.
LYN ROGERS
It landed there, and that front of the magnet there is where we read it from.
VOICEOVER
The true measurement is the average of these two distances.
You can also use a black disc and periscope viewer to measure water clarity. This equipment works well down to about 10 cm visibility. You will need two to three people for this.
Low visual clarity is an indicator of poor stream health. Fine sediment causing the high turbidity will clog the gills of fish and macroinvertebrates. They cannot survive in such conditions.
Visual clarity can be changeable depending on weather patterns. For example, high rainfall events can cause high turbidity for short periods of time. It is important to measure a range of indicators and often when assessing overall stream health.
Acknowledgements
Aroha Salu Alicia Caitlin Waikato Regional Council Lynnette Rogers The Fairfield Project Jordan, Lucy, Hannah, Jess and Sam, Waikato Diocesan School for Girls Jake and Sarah, Bankwood Primary School
Acknowledgement
This video has been developed in partnership with the Waikato Regional Council as part of the Rivers and Us resource.
