Keeping leaves out of the street is an important step homeowners can take to protect water quality in Minnesota's lakes and streams. Leaves are a source of phosphorus that can degrade water quality, said Bob Mugaas, Hennepin County educator with the University of Minnesota Extension Service.
"When leaves fall from our deciduous trees in the fall, they often accumulate on hard surface areas such as streets and driveways," said Mugaas. "Then they may begin to decompose, releasing both organic and inorganic forms of phosphorus. When it rains runoff water can carry this phosphorus into storm sewers and then into nearby bodies of water."
"As cars travel over leaves in streets and driveways, they further grind up the leaves, making them even more susceptible to decomposing while lying on the street."
When there is a heavy rainfall, leaves themselves can be carried directly into lakes and rivers, said Mugaas. Tree leaves can also blow directly into lakes, ponds, and lakes and rivers.
During the growing season, and especially in the spring, tree seeds and sometimes fruits are often dropped liberally onto the ground and the street. "Just as with leaves, traffic driving over these materials crushes them and breaks them up, making them easier to decompose or be carried away in runoff water," said Mugaas. "Like leaves, these materials contain phosphorus and other plant nutrients."
Mugaas does not advocate eliminating trees from our surroundings. "What we can do," he said, "is to keep our street areas clean of leaves and seeds. We can rake or sweep them up during the growing season, especially spring and fall. They can be used for mulching other areas of the landscape. In the case of seeds and fruits, it may be a good idea to compost them to avoid having little tree seedlings sprouting all over the landscape."
Keeping leaves out of the driveways and streets in front of our homes is a way we can each contribute to cleaner runoff and cleaner lakes and streams, said Mugaas. "And it should go without saying that we should not blow grass clippings into the street or onto hard surface areas where they can run off," he adds. "Blow clippings back onto the lawn where they can be chopped up even further with consecutive passes of the mower. Keeping lawn clippings on the lawn contributes the equivalent of about one to one and one-half applications of fertilizer per year back to your lawn."