When it rains, it pollutes!
When it comes to stormwater, we’re all part of the problem. Fortunately, that means we can all be part of the solution. Click on the links below to learn more about reducing stormwater pollution:
The Natural Water Cycle
Water on Earth is always changing, and its repeating changes make a cycle. As water goes through its cycle, it can be a solid (ice), a liquid (water), or a gas (water vapor). Ice can change to become water or water vapor. Water can change to become ice or water vapor. Water vapor can change to become ice or water.
How do these changes happen? Adding or subtracting heat makes the cycle work. If heat is added to ice, it melts. If heat is added to water, it evaporates. Evaporation turns liquid water into a gas called water vapor.
If heat is taken away from water vapor, it condenses. Condensation turns water vapor into a liquid. If heat is taken away from liquid water, it freezes to become ice.
The water cycle is called the hydrologic cycle. In the hydrologic cycle, water from oceans, lakes, swamps, rivers, plants, and even you, can turn into water vapor. Water vapor condenses into millions of tiny droplets that form clouds. Clouds lose their water as rain or snow, which is called precipitation. Precipitation is either absorbed into the ground or runs off into rivers. Water that was absorbed into the ground is taken up by plants. Plants lose water from their surfaces as vapor back into the atmosphere. Water that runs off into rivers flows into ponds, lakes, or oceans where it evaporates back into the atmosphere. And the cycle continues…
Man-Made Water Cycle
Trouble for water quality and quantity begins when areas are developed, since development dramatically alters the natural water cycle. Trees that had intercepted rainfall are removed. Natural depressions that had temporarily held water are graded to a uniform slope. The spongy layer of forest floor that had absorbed rainfall is scraped off, eroded, or severely compacted. Having lost its natural storage capacity, a cleared and graded site can no longer prevent rainfall from being rapidly converted into stormwater runoff.
The situation worsens after construction: rooftops, roads, parking lots, driveways and other impervious surfaces no longer allow rainfall to percolate into the ground. The increase in impervious surfaces also decreases natural recharge of groundwater, a source of drinking water for residents of many watersheds. Urban land uses also degrade groundwater quality, if stormwater runoff is directed rapidly into soil without adequate treatment.
The substances on these surfaces — nutrients like phosphorus and nitrogen; sediment; bacteria; hydrocarbon compounds like gas and motor oil; metals; pesticides; trash; and road salt — are all stormwater pollutants that are delivered to downstream waters.
Rain and melting snow act like a water hose, washing the landscape free of loose dirt and grime. While a good washing helps spruce up our communities after a long winter or summer dry spell, it does little for the health of our rivers, lakes and wetlands. That is because materials washed off the hard surfaces in our towns and cities eventually end up in the water, where they can become harmful pollutants.
Pollution caused by rain and snowmelt washing the landscape goes by several names. It is called stormwater pollution because it is caused by storms, runoff pollution because it is carried by rain and snowmelt runoff, and nonpoint-source water pollution, a technical name meaning it is different than point-source water pollution. Point source water pollution is the type of water pollution that comes from an industrial or wastewater discharge pipe — a definite point, or location, on the landscape.
Controlling stormwater pollution is a challenge because sources of pollution come from many locations across the landscape and is associated with weather — something we cannot control. Controlling stormwater pollution requires everyone’s action, from the homeowner to the business owner, from the road builder to the street sweeper.
The main stormwater pollutants harming Minnesota’s water are:
Sediment is dirt from our roads, and eroded soil. A major source of sediment in urban areas is construction sites where exposed soil is easily washed or blown away. Once it finds its way to water, sediment fills in rivers, lakes and wetlands, destroying wildlife habitat, interfering with recreation, and causing flooding. Sediment also carries other stormwater pollutants with it, such as nutrients and toxics which adhere to soil particles.
Nutrients are plant food, which by itself is a good thing — fertilizers help our gardens, lawns and farm fields grow — but too much plant food entering water can cause an overabundance of algae growth. Algae are small free-floating water plants that turn water green, slimy, and smelly when they grow in abundance. The nutrient of most concern is phosphorus — one extra pound of phosphorus added to a lake can produce up to 500 pounds of algae! Phosphorus is the biggest pollution problem for Minnesota lakes, so the Minnesota legislature passed the Phosphorus Lawn Fertilizer Law, which restricts the use of phosphorus-containing lawn fertilizer.
High levels of fecal bacteria, the bacteria found in feces, have caused swimming beaches to close in the Twin Cities metro area. The bacteria come from pet and wildlife feces that wash into the lakes with stormwater. Pick up after your pet.
Toxics refer to such poisons as pesticides, salt, and metals such as lead, copper and zinc. Sources of toxic materials vary greatly and include yard chemicals, road salt, seepage from storage yards, and metals coming off roofing materials and car brake pads. Although more alarming-sounding than sediment and nutrients, effects of toxic materials on lakes and rivers are harder to identify. Studies in the Twin Cities, however, show that the numbers of different types of plants and animals in wetlands with high levels of chloride (salt), zinc and copper are lower than what are found in natural wetlands.
It might be hard to think of heat as a pollutant unless you’re a cold-water fish such as trout. Trout require water temperatures of 60 to 65 degrees. Stormwater running off hot roofs, roads and parking lots in the summer can easily raise stream temperatures above what is safe for trout. With all our hard surfaces that heat up in the summer, keeping cool is a big challenge for CRWD’s lakes and the Mississippi River.
How Students Can Take Action
Anyone can help reduce water pollution! In fact, city and state agencies cannot do it alone…long-term improvement of water quality depends on citizens getting involved in the solution, and that’s where students come in. Projects can be carried out through a variety of formats: through your youth group or extracurricular club; through integration into life science, earth science, biology, civics, or other academic course; through a one-time all-school project (for example, on Earth Day, Arbor Day); older students working with younger students; or through student advocacy for water-related policy, to name a few.
Follow these steps for any project:
- Research your watershed
- Identify the problem or exploration you try to solve
- Develop partnerships to explore the issue
- Organize and take action (see Action Steps below)
- Compile and analyze your results and the process you used. What worked well? What should have been done differently?
- Report your results. What did you discover? Who might want to know? How could you get the information to those people or groups?
Identify a need Ask local watershed agencies what practices they most want to citizens to adopt. Your own student research may uncover a new problem.
Target an audience To increase success, narrow your audience to a manageable size according to geography, behavior, or demographics.
Decide how best to speak What most interests your audience? Where do they get information? What concerns to they have? What arguments are most convincing?
Choose a method of communication Local print newspapers, present to younger elementary students, produce a video clip for YouTube, create a display or booth
Study the history of Loeb Lake and produce a theater performance
At a farmer’s market or community festival, use a watershed model to illustrate how street pollutants enter the Mississippi River
Organize a clean-up of a stretch of street; emphasize to participants that whatever is in the street ends up in the Mississippi River via storm drains
Organize a free storm drain stenciling activity with Friends of the Mississippi River
Water cycle images provided by Charles River Watershed Association.