The Invisible Pollution of Urban Waterways

Photo of a storm drain with water flowing into it.
photograph by Mississippi Watershed Management Organization, distributed under a CC-BY 2.0 license

You know not to litter, you know to not dump dangerous chemicals, but did you know that you might be unintentionally contributing nutrient pollutants to waterways?

Because most land in urban areas is covered in impermeable surfaces like concrete, asphalt, and compacted dirt, rain water can’t soak into the ground. Instead, rain enters storm drains in large volumes, and it then empties into creeks and streams at high velocities. It picks up and carries a wide variety of pollutants from streets, driveways, and yards, into local waterways.

While styrofoam, plastic, and oil slicks are obvious pollutants, there are also invisible pollutants that can tip a creek ecosystem into collapse. Soapy water, grass clippings, fertilizers, and pet waste are often picked up by rainwater, enter a storm drain, then are dumped into local creeks and streams. These pollutants kill wildlife and plants in addition to potentially degrading the quality of drinking water.

While they each have additional negative environmental effects, grass clippings, fertilizers, pet waste, and some soaps contain necessary plant macronutrients like nitrogen, phosphorous, and potassium. While more nutrients sounds like a good thing, these pollutants harm life in the waterways by changing the balance of the ecosystem. 

In a healthy ecosystem, plant growth is limited by the availability of macronutrients. When humans introduce large amounts of these nutrients to waterways, lakes, and oceans, algae reproduction explodes. With such a large amount of nutrients available, these microscopic photosynthesizers will continue to grow. When they die, the aerobic bacteria that break them down use up all of the oxygen suspended in the water. This is called eutrophication or an algae bloom.

When an algae bloom occurs, it kills all life in the oxygen depleted water, ultimately including the remaining algae. As the algae and other organisms decompose, they release carbon dioxide, which bonds with water to become carbonic acid. This makes the water more acidic, which harms a wide variety of living things, especially mollusks like snails and mussels. In addition, some algae species also produce chemicals that are toxic to wildlife. In sufficient quantities, these harmful algae blooms can overwhelm water treatment facilities and make tap water undrinkable.

There are a number of ways you can help reduce excessive nutrients in waterways. The most important thing to remember is to always be mindful of drainage. Taking your car to a car wash means that the soap, oil, and other grime will be washed into a sewer drain where it will be treated. If you have a lawn, make sure to always leave the clippings on the yard, instead of bagging them or pushing them into the street. Before using fertilizers, always get a soil test from your local agricultural extension service to determine what type and amount you need. In addition, make sure to water in the fertilizer and not apply it if there is rain forecast soon. And lastly, if you have a dog, make sure their waste won’t make it into a storm drain.

With your help, we can create a better urban environment for animals, plants, and humans.

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