Autumn, otherwise known as fall, is the most dramatic time of year. The leaves are turning scarlet, yellow and orange and are dropping from the trees. It’s a beautiful display! The air smells of pumpkin soup and apple cider, we hear the sound of fewer lawn mowers and more leaves crunching underfoot. But what is going to happen to those leaves? Some will blow to various places in our neighborhoods, some might feed the soil that feeds next year’s garden if you compost them in a garden bed. The thing we don’t want to do is waste them by letting them wash down the street and into the storm drains the next time it rains.

Stormwater picks up everything in its path, and stormwater doesn’t get treated at the wastewater treatment plant. Our street storm drains dump directly into the nearest river or lake, and that stormwater eventually flows into the Cannon River.

Now I know what you’re thinking, “Kevin, leaves have been blowing into rivers since the beginning of time,” and that’s true. Rivers can deal with some leaves in the river. Over millions of years, river and lake organisms have evolved to consume some nutrients. So if the 500 trees near the river in Northfield drop their leaves and some of those leaves blow into the river, that’s not a big deal. But our efficient city storm drain systems can now carry leaves from every tree in town to the river. That could mean the leaves of 5,000 trees could wash right into the river. And that’s one source for the excess fertilizers that can turn our rivers and lakes green with algae.

Once in a body of water, our leaves will be crunched up and dissolved into a nutrient-rich soup that adds tons of phosphorus to the rivers and lakes. That phosphorus is the favorite food of algae that creates the “green slime” on the water. How much phosphorus do we have control over? For example, in the amount of leaves that it takes to fill five garbage bags, there is about 1 pound of phosphorus, which can turn into 1,000 pounds of algae. Ick!

Luckily, it’s a problem with an easy solution. Instead of raking or blowing your leaves into the street, bag them and take them to the city of Northfield compost site or compost them in your own yard. Spread them on garden beds or mulch them with a mower onto the lawn for a no-cost fertilizer.

Keep in mind that “pollution” is really “the right stuff in the wrong place.” Mulched leaves are great fertilizer in the garden, but it can be a pollutant on streets and in storm drains. But lucky for us, it’s a pollutant that’s easy to fix, just by collecting and disposing of our leaves and cleaning out our storm drains.

Don’t let the river get too much of a good thing — use those leaves yourself or let someone else turn them into compost and you’ll be doing your part for a cleaner river or lake for many more seasons to come.

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