By Madeline Leslie, Graduate Research Assistant
Residents of the Minneapolis-St. Paul Metropolitan area are lucky enough to have a plethora of valuable water resources on their doorsteps. Numerous lakes and streams are available for swimming, fishing, boating, and other recreational activities. However, in part due to their being located in densely populated urban areas, these bodies of water sometimes can become too polluted to be used for recreation, or even to support native aquatic life. One major source of pollution is excess nitrogen and phosphorus running off of land into lakes, rivers, or streams. These nutrients are found in fertilizers as well as naturally attached to soil particles, and can cause large algae blooms in water bodies. The reduced water clarity and low oxygen levels that often accompany such blooms are detrimental to aquatic plant and animal life and also make for very unpleasant swimming conditions. In addition, some types of algae that form these blooms can produce toxins that are harmful to people and their pets.
While efforts have been made to improve water quality in the state, such as the passage of the Minnesota Phosphorus Law in 2002, many problems still exist. In 2013, the Minnesota Pollution Control Agency (MPCA) published a report, which found that over half the lakes assessed in the Mississippi River-Twin Cities Watershed were impaired by nutrient pollution. Which begs the question: where is all this pollution coming from? The answer is that most urban areas have an overabundance of impervious surfaces, such as streets, driveways, parking lots, etc. As demonstrated by a diagram created by the Environmental Protection Agency (EPA) in Figure 1, impervious surfaces do not allow rainwater to infiltrate into the ground. Rather, the runoff water drains into the storm sewer system, which in the Twin Cities is not treated, but heads directly to a lake, river, or stream. Along with the runoff water goes any excess fertilizer or loose soil that might be in someone’s yard or driveway, and there you have it: nutrient pollution.
In urban spaces where land is divided up into numerous small parcels, controlling what runs out of each yard is very difficult, as there are multiple reasons why nutrient runoff might occur. However, most homeowners can make minor changes to the way they manage their lawns and gardens in order to reduce [Read more…]