Nitrogen, phosphorus from fertilizers and pet waste polluting urban water.
The study—published in the Proceedings of the National Academy of Sciences—is the first to compare the urban watershed budgets of nitrogen and phosphorus.
And the results can be applied to urban watersheds around the world impaired by excess nutrients.
The research team—led by Sarah Hobbie, Distinguished McKnight University Professor in the Department of Ecology, Evolution & Behavior and an Institute on the Environment Fellow—discovered households are the main sources of nutrient pollutants in the Twin Cities urban watershed.
Urban watersheds are highly "leaky" with regard to nutrient pollution because of their dense networks of streets and storm drains, which are designed to readily move water off the landscape to avoid flooding.
As a result, most of the phosphorus entering urban watersheds ends up being carried away by stormwater that drains into surface waters and thus contributes to pollution and eutrophication.
Nitrogen tends to disperse through more diverse pathways—about one-fifth is transported via stormwater into surface water while much of the rest ends up either being released into the atmosphere or moving through soil into groundwater.
"Urban waters—lakes, streams, rivers, coastal waters—continue to be impaired by nutrient pollution, especially phosphorus, despite long-running efforts to clean them up," said Hobbie.
"Not only is this a concern for water resource managers tasked with cleaning up urban pollution, but also urban and downstream residents who depend on clean water for drinking water, recreation and aesthetic value."
More information: Contrasting nitrogen and phosphorus budgets in urban watersheds and implications for managing urban water pollution, PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1618536114