A University of Minnesota study showed decaying leaves from streets and storm drains have caused phosphorus to pile up in local bodies of water, affecting more than 140 lakes in the Twin Cities.
St. Thomas biology professor Chip Small said too much phosphorus from leaves can have a minor effect on the Mississippi River as well, causing water to appear green and smell bad.
“Nutrients get leeched out of those leaves and go straight into the gutters, and it turns out that’s actually a pretty significant fraction of the phosphorus,” Small said. “The water just flushes whatever is in the streets into the storm sewers … and those go out directly into the river.”
Sophomore Andy Hobday said after learning about the issue, he will be more conscious about raking.
“I want to do what I can to help out, so I’m raking,” Hobday said.
Roger Weinbrenner, lead staff member for the St. Thomas grounds department, said the staff mows frequently to help cut back on phosphorus levels.
“We use mulching kits on the bottom of our mowers,” Weinbrenner said. “It breaks (leaves) up in very small pieces.”
Though it is important to cut back on phosphorus, Small said overly-nutritious leaves are not the biggest problem the river is facing.
“Runoff from farmland is probably the main thing we need to focus on,” Small said. “But for this study for the impact of leaves, I think that’s more of a local impact in local streams and lakes.”
Hobday said the Mississippi River is one of the main reasons he loves St. Thomas and hopes his help can improve river conditions.
“(The river) is my favorite place here; this is why I go to St. Thomas,” Hobday said. “I’m doing what I can to help out.”
Alison Bengtson can be reached at firstname.lastname@example.org.