STORMWATER POLLUTANTS

When it rains, it pollutes!

Unfortunately, this is too often true. 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 land 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. It is a challenge because sourses 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
• Nutrients
• Microorganisms
• Toxics
• Heat

Throughout this website, pointers are given on how we can Get Involved to keep pollutants from getting into the rivers, lakes, and wetlands that make Minnesota so special.

Sediment

Sediment is, well — it’s dirt! Road dirt 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 we will talk about soon. Sediment is the biggest pollution problem for Minnesota streams and rivers.

Back to top of page

Nutrients

Nutrients are plant food. Plant food in 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 in phosphorus — one extra pound of phosphorus added to a lake can produce up to 500 pounds of algae! That is why Minnesota passed the Phosphorus Lawn Fertilizer Law, which restricts the use of phosphorus-containing lawn fertilizer. Phosphorus is the biggest pollution problem for Minnesota lakes. Minnesota has completed a Statewide Phosphorus Report which outlines the sources of phosphorus pollution across the state.

Back to top of page

Microorganisms

Microorganisms: High levels of fecal bacteria, bacteria found in feces, have caused swimming beach closing in the Twin Cities metro area. The bacteria are not of human origin, but come from pet and wildlife feces that wash into the lakes with stormwater. In 1993, a Milwaukee drinking water treatment plant malfunction allowed high levels of the protozoa cryptosporidium to enter the drinking-water system, causing 400,000 people to fall ill. Runoff of livestock feces during spring snowmelt is a suspected source of the outbreak.

Back to top of page

Toxics

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-care 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 Minnesota rivers, lakes and wetlands 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.

Back to top of page

Heat

Heat: It might be hard to think of heat as a pollutant, but it is if you are a cold-water fish such as a trout! Trout require water with "sweater weather" temperatures — 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. One of the biggest challenges for Twin Cities trout streams, such as Browns Creek near Stillwater, the Vermillion River near Lakeville, and Assumption Creek near Chanhassen, is "keeping their cool."

Back to top of page