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Ask Dr. Universe: Plants and animals are vital parts of a river’s ecosystem

Sept. 11, 2022 Updated Sun., Sept. 11, 2022 at 3:37 p.m.

A river's ecosystem relies on a balance between plants and animals, such as this great blue heron spotted above the Spokane River north of the Nine Mile Dam recently.    (Dan Pelle/The Spokesman-Review)
A river's ecosystem relies on a balance between plants and animals, such as this great blue heron spotted above the Spokane River north of the Nine Mile Dam recently.   (Dan Pelle/The Spokesman-Review)
By Washington State University

Washington State University

Dr. Universe: How can plants help rivers?

Jaydon, 9, Charlestown, Indiana

Dear Jaydon,

Rivers are great places for kids to explore. With an adult and a safe stretch of water, you can wade, swim, splash and enjoy the incredible number of animals that make the river their home – along with all the plant life. Many types of plants grow around rivers. You’ve already guessed how important they are to keeping rivers healthy!

To learn more, I talked to my friend Alex Fremier, an associate professor at Washington State University’s School of the Environment who works with the State of Washington Water Research Center.

Fremier studies areas called watersheds. A river’s watershed is made up of all the land where rain and snow fall and drain down hills and through streams into the river.

The plants in a watershed soak up some water before it reaches the river. They also help filter out pollutants in the water that makes it all the way there.

“If you removed all the plants, then the water would drop on the soil and dislodge that soil, and that soil would enter the streams and pollute them,” Fremier said.

Some rivers have lots of soil in them, like the muddy Mississippi, while others run more clear. Either way, the animals that live in a river are used to a certain amount of dirt in the water. Plants in the watershed help keep that amount steady, which keeps the animals healthy.

Rain and soil can bring other pollutants with them, too. Plants help filter out pesticides or fertilizers from crops and chemicals from roads.

The plants that grow along a river’s banks are helpful, too. We call these plants “riparian” (RY-PAIR-EE-AN). Riparian plants are the final filters between the land and water. They also hang over the water, keeping the river cool. A steady temperature is important for river animals.

For example, Fremier said, “salmon need cool, clean water, and if if the sun is hitting the water’s surface, that water is going to warm up.”

Finally, there are plants growing in the river. If you’ve ever touched river rocks, you’ve felt the slimy brown or green algae (AL-GEE) that grows there. Algae are plants! They pull chemicals like nitrogen and phosphorus from the river water to help them grow.

Fremier encourages kids to think about all the ways plants help rivers by observing algae. The next time you’re at a river, pick up a rock. Look at the algae and other tiny plants growing on the surface. Then flip the rock over and look at the back. If the water is clean, you’ll see tiny baby insects.

The algae and insects are both part of the river’s ecosystem – just like the huge trees in the watershed, the ferns growing along the bank and the salmon swimming in the water. A healthy ecosystem needs many parts, working together.

People are part of the river’s ecosystem, too. Keep being curious and asking questions, and you can be part of the big team that helps keep the water clean for all the wonderful things that live in and by a river.


Dr. Universe

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