As we flip the calendar from September to October, we start to think about the beautiful autumn colors of the Ozarks. However, autumn leaves can actually contribute nutrients to our local waterways. This blog by Stephen A. Hubbs, professional engineer from Kentucky with the water quality and health council explains the connection between increased nutrients in our water and the autumn leaves which fall from our trees. Access the complete article here.
Today, a major concern is that leaf litter (i.e., organic debris) spikes stormwater systems and watersheds with nutrients during and after rainfall, especially when it gathers along street curbs. Excess phosphorus and nitrogen often lead to major water quality problems for municipalities, a process called eutrophication,1 and harmful algal blooms (HABs). The sources of nitrogen and phosphorus are many and varied, but leaves that fall on streets and into catch-basins during autumn can add to the nutrient problem in urban streams and lakes—particularly in subsequent summer months that also support conditions for HABs.
The connection between fallen leaves and excess nutrient loading may appear intuitive, but the impact on urban water quality, including release of organic compounds, is not fully understood. A U.S. Geological Survey researcher named William Selbig reported on research conducted during the months of April through November, 2013 to 2015, in Madison, Wisconsin.3 He noted that “While the sources of nutrients to urban stormwater are many, the primary contributor is often organic detritus, especially in areas with dense overhead tree canopy … making source control through leaf removal one of the few treatment options available to environmental managers when reducing the amount of dissolved nutrients in stormwater runoff.”
So What Can I Do?
Think regionally (area streams and lakes) and act locally (your front yard). There are several things you can do this fall to reduce the effect of leaves on urban water quality:
- Consider mulching in-place with your lawn mower, especially if your yard is relatively flat, and those nutrients will soak into your lawn.4 And it’s probably easier than raking!
- Gather leaves and other “yard waste” into a compost pile for use next spring to fertilize flower beds and vegetable gardens.
- If you know when leaves will be collected for your community, wait to rake them close to the street until just before collection time.
- If you have curbside leaf collection, rake leaves near the edge of the street (keep about three feet of lawn between the curb and the pile) but not into the street. The soil under the leaves will adsorb some of the nutrients when it rains.
- Keep leaves off driveways, sidewalks and other impermeable surfaces.
- Keep the streets and catch-basins free of leaves … they usually lead straight to a stream!