Sweeping for cleaner lakes

Angie Hong
Water Columnist

If a leaf falls in the forest and nobody sees it, do you still have to rake it up?

Every autumn, the air cools, leaves change color and fall, and a million Minnesotans grab rakes and shuffle outside grumbling to rake the leaves out of their yards. Interestingly, research from the University of Minnesota indicates that mowing the leaves into your lawn may actually be better for your grass than raking because it allows nutrients from the leaves to break down and replenish the soil. On the other hand, many people don’t think to rake leaves out of the street in front of their homes, but doing so is an easy and important way that everyone can help to protect local lakes.

Why rake the road instead of your yard? Consider the contrast between what happens to fallen leaves in a forest or on your lawn, versus those on the street. In forests, earthworms, insects, fungi, and bacteria break down and decompose the leaves over time. As a result, phosphorus and nitrogen that’s been absorbed by trees is returned to the soil and helps to spur new growth in the spring. Mowing leaves into your lawn achieves a similar result. Leaves in the street also break down, but when they do, the released nutrients flow into storm drains that connect to wetlands, lakes and rivers. The result is smelly green water, filled with algae.

Stormwater pollution is a major problem for lakes and rivers in Minnesota, and excess nutrients impact water quality in Clear Lake, Comfort Lake, Forest Lake, Shields Lake, and the Sunrise River. This year, the Comfort Lake – Forest Lake Watershed District received a $36,000 Minnesota Clean Water Fund grant to develop an enhanced street sweeping plan for the city of Forest Lake. The goal is to get more leaves and debris out of the street so that there is less phosphorus flowing into local lakes. Cleaner streets mean cleaner water.

Currently, Forest Lake sweeps its streets twice per year with a mechanical broom sweeper in order to improve road safety and keep the streets looking good. By doing so, the city removes an estimated 127 pounds of phosphorus and 148,188 pounds of solids each year. For perspective, one pound of phosphorus can grow 500 pounds of algae! However, analysis conducted by Emmons & Olivier Resources, Inc. for the Comfort Lake – Forest Lake Watershed District indicates that the city could keep an additional 137 pounds of phosphorus and 169,793 pounds of solids out of local lakes if it began sweeping twice a month with a regenerative air sweeper. In addition, EOR suggests that the city could use an in-house sweeping program and increase the frequency of sweeping on streets nearest lakes and stormwater ponds for the same cost as the current sweeping contract.

Though the city of Forest Lake and the Comfort Lake – Forest Lake Watershed District hope to implement a more robust street sweeping program in the future, it will still be important for citizens to do their part to keep leaves, grass clippings, and other debris out of the roads in front of their homes. There are 240 lane miles of streets to be swept in the city, and it takes a long time for a slow-moving machine to complete the work. Citizens help to keep streets clean between scheduled sweeping times and can also remove the top layer of debris so that the sweeping machines are better able to remove sand and silt below, which are often full of heavy metals, nutrients and hydrocarbons.

The good news is that Minnesotans are already well-trained at how to use a rake, so it should be easy to start a new habit. Stop raking the lawn and start sweeping your street instead. The lakes will be cleaner, and your neighborhood will look good too.

Angie Hong is an educator for East Metro Water. Contact her at 651-330-8220 x.35 or [email protected]