The Green Guy: Leaves are pretty in the fall, pretty dangerous for water

The recent wind and rain have taken a toll on the leaves. In turn, the crinkly debris is strewn all over, leading to the debate on collecting or ignoring them. Whatever side of the fence you sit on regarding handling the leaves, one place they most assuredly shouldn’t be is the street.

Why? Because the end destination, come the next rain, is a nearby storm drain leading to a nearby water feature.

“What’s the big deal?” you might ask.

Let me explain.

When fall approaches, trees begin taking nutrients from their leaves in preparing a cache of resources for the winter. However, not everything is taken out of the leaf — what remains is a mix of carbon, nitrogen and phosphorus. These three primary components and a couple of others are, in turn, beneficial to the plants below or your lawn — especially if mulched into small pieces that decompose easily.

However, what’s good for the grass isn’t necessarily good elsewhere. Specifically, I’m talking about waterways. I’ve mentioned this before, but it’s worth repeating: nutrients and our waterways shouldn’t mix.

When leaves enter our storm drains, they concentrate nutrients near the outlets, causing issues downstream. Particularly concerning is the phosphorus and nitrogen content which promotes algae blooms, and it takes very little to do so. The analogy that an ecosystem is like a recipe should come to mind with regard to nutrients: proper proportions are key to success in both. Hence, the entry of extra organic debris, in the form of leaves, begins to throw things off.

Also, when leaves get matted, they block nooks and crannies needed by aquatic life. When enough leaves pile up in slow flowing areas, insects residing below are cut off, as are spaces for young fish. Moreover, the leaf-mat can remain for a fair amount of time, as being submerged make the breakdown process longer.

Now, you might be wondering about trees along shores. Aren’t they a problem, just like street trees? The answer is a matter of concentration. The number of trees along a shore is minimal compared to the number of trees across a whole town, even a neighborhood, so the amount of debris from shoreline trees is a small dose compared to the piles of leaves in a city. Further, the trees along a shore are part of that local system, so what breaks down from their leaves originally came from nearby.

So what’s the point in saying all this? To bring attention to the leaves likely piled up and cluttering your street’s storm drains. This is one of the most important times of the year to make time to clear leaves and debris away from curbs and drains. Please spend the few minutes it takes over these next couple of weekends keeping the crinkly mess out of our streets and, ultimately, out of our waterways.

Chris Gass is the education and outreach coordinator for the Carlton Soil and Water Conservation District whose columns focus on environmental topics and stewardship.