Nutrient Pollution in the Mississippi River-Twin Cities Watershed: How Outreach Efforts can be Informed by the Relationship Between Individual Water Pathway Knowledge and Lawn Maintenance Practices

June 30, 2015

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.

Figure 1: Illustration of the relationship between impervious surfaces and surface runoff
Figure 1: Illustration of the relationship between impervious surfaces and surface runoff

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[1], 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[2], 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 phosphorus and nitrogen losses from their property. This includes not over-applying fertilizer, reducing watering, repairing bare soil patches, keeping leaves and grass out of street gutters, and selecting low-input turfgrass species to be used in lawns. The challenge arises when trying to convince a very diverse group of people to change their behavior.

To find more information about the reasons why an individual might more often do harmful rather than beneficial lawn maintenance practices, two surveys were conducted of homeowners in the Twin-Cities area. The first was released in July of 2014 and the second in April of 2015. Both were conducted online via the survey tool Qualtrics and each had slightly over 300 complete responses. The questions on both surveys were regarding the frequency of lawn or yard maintenance practices, water pathway knowledge, the effects of lawn maintenance behavior on others, and demographics. Additionally, participants in both surveys watched a short educational video on water quality in the Twin Cities area, which was used to help gauge whether or not this method of outreach would be effective in encouraging positive behavior change regarding lawn or yard maintenance activities. Half of the participants in the second survey read an educational pamphlet online instead of watching the video.

The first survey found that 31.8% of respondents had inaccurate perceptions of the path water travelled when it left their yard. That is, they thought storm sewer system water was treated, or that it did not reach a lake, stream, or river. The second survey found that 31.7% of respondents had inaccurate water pathway perceptions. In both cases, having inaccurate perceptions was associated with doing lawn or yard maintenance practices more frequently, particularly mowing and fertilizing. In addition, those with inaccurate perceptions also were much more likely to believe that their maintenance practices had no effect on local water quality when compared to those with accurate perceptions.

Regarding the effect of the educational video intervention, respondents to the first survey were given a follow-up survey three weeks after their initial participation. While it was found that a large percentage of individuals said they had reduced watering and looked for fine fescue turfgrass seed after watching the video, the results for other maintenance behaviors were less informative. This is likely because some behaviors such as fertilizer or pesticide application often only occur once or twice a year in the spring or fall. Due to this limitation, respondents of the second survey were asked only about the frequency with which they intended to do certain maintenance activities in the future. After watching the video, it was found that all participants intended to water less, fill in bare lawn patches, and prevent fertilizer and organic material from getting in the street significantly more often. Those who responded to the second survey reported a greater intent to beneficially change their behavior after reading the pamphlet compared to those who watched the video.

It is clear that the Twin Cities area still has a long way to go before adequate progress is made in reducing nutrient pollution in local lakes, rivers, and streams. Due to the disparate nature of the source of this pollution, it is important to consider many different strategies when attempting to create widespread behavior change that will help reduce nitrogen and phosphorus losses from individually owned parcels of land. One such method is public education on the physical connections between private property and the local watershed. According to the results of these two surveys, this type of education will be effective in changing watering and turf species selection behavior among about a third of respondents, and very effective at changing participants’ intent to do beneficial maintenance practices more often, especially when reading educational material as opposed to watching a video. With the help of this information, we have moved one step closer to reducing nutrient pollution and preserving our water resources for all future generations to come.


[1] Minnesota Pollution Control Agency. 2013. Mississippi River-Twin Cities Watershed Monitoring and Assessment Report.

[2] US Environmental Protection Agency. 2003. Protecting water quality from urban runoff. Document No. EPA 841-F-03-003