As the trees lose their beautiful fall leaves, they tend to pile up in our yards and streets. Those leaves contain phosphorus, an essential nutrient for plant growth. As the leaves decompose, they release the phosphorus that was bound up in the leaf. When it rains, the phosphorus is washed down the street, down the nearest storm drain, and out into the nearest lake, river, or stream. There it is — a bountiful source for algal growth that causes excessive algae blooms.
A recent study by the University of Minnesota found that up to 60 percent of damage to urban lakes caused by excess nutrients (phosphorus) is a result of leaf litter decomposition. In a forest, leaves decay on the forest floor, where the phosphorus is able to return to the soil and be reused by plants. In cities, on hard surfaces like driveways and streets, the phosphorus is unable to return to the soil and instead washes away with the rain.
Some cities have street sweeping or leaf pick up services already in place. However, many cities need the help of local residents on tackling the leaf issue. Enjoy these last beautiful warm fall days outside, raking and bagging the leaves in your lot. The leaves in the street are the most important to remove. They can be dropped off at the local compost site. Raking up just five bags of leaves keeps a pound of phosphorus out of stormwater runoff. This may not seem like a lot, but just one pound of phosphorus is able to feed and produce 1,000 pounds of algae in a lake.
Some citizens have started “Community Clean Up” events, days where residents get together to rake and bag leaves off the street. There are free toolkits available for hosting such events through the Freshwater Society. To request a kit, email email@example.com. It’s a small chore that can make a big impact!