Water quality under the microscope
11 January 2021

Water quality under the microscope

Have you ever wondered how healthy our watercourses are? How do we measure this?

Renowned aquatic ecologist, Peri Coleman recently joined council’s Parks and Natural Resources team and local families to put the health of the Onkaparinga River at Old Noarlunga under a microscope.

Aquatic macro invertebrates (water bugs) were used as indicators to estimate the quality of water in the river.

“A polluted stream will only have a few types of invertebrate species present that can tolerate pollution,” Nikola Manos, council’s Nature Conservation Project Officer explained.

“A less polluted stream has a greater variety, including species that are sensitive to pollution.”

Weather conditions and flow of the river can also affect results.

While this was not a rigorous scientific study, the group’s observations showed that the river at Old Noarlunga—on that particular day—was healthy. This was due to finding an emerging Mayfly—which are very sensitive to pollution—seeing crab larvae, and getting a nine out of 10 SIGNAL (stream invertebrate grade number – average level).

“We collected the water bugs, including caddisfly, by scraping nets along the muddy edges, around plants and rocks in the river.

“We tipped the contents from the nets into trays and used magnifying glasses and microscopes to really get a good look and try and work out what each creature was.”

“With much excitement and help from books, identification charts and Peri, we discovered four different types of molluscs (mussels and snails), two types of arachnids, some tiny worms and many crustaceans and insects. We also saw dragonfly and crab larvae and a small fish which we believe was a Blue-spot Goby.

“A highlight was finding caddisfly, which we initially thought were just twigs, until they started moving.

“We learned that caddisfly larvae make little mobile homes for themselves out of twigs and things they find in the stream. They walk around with the stick, similar to what hermit crabs do with their shells, to protect them from predators.

“The purpose of the event was to get people curious about their river by discovering biodiversity on a different, smaller scale and make a connection between land and water habitats.”

All the bugs were put back in the water at the end of the event.

If you want to find out more about waterbugs and how to become a citizen scientist to assess the health of a waterway near you, there are lots of ways to get involved.

This event was part of the one-year habitat restoration project, Urban Creek Recovery – Onkaparinga River at Old Noarlunga. The project is supported with funding through the Australian Government’s Communities Environment Program.

“We really enjoy opportunities to learn new things with our communities and we hope to run more events like this in the future,” Nikola says.

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