Nitrogen, phosphorus from fertilizers and pet waste polluting urban water

New research from the University of Minnesota points to lawn fertilizers and pet wasteWaste consists of unwanted and thrown away goods that often still have value as fuel or raw material. as the dominant sources of nitrogen and phosphorus pollutants in seven sub-watersheds of the Mississippi River in Saint Paul, Minnesota.

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. Household nitrogen fertilizer use in particular is more than 10 times greater than commercial fertilizer use by golf courses, college campuses and other non-residential locations, and pet waste is the leading source of phosphorus to these watersheds.

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 waterClimate change is expected to exacerbate current stresses on water resources from population growth and economic and land-use change, including urbanisation. On a regional scale, mountain snow pack, glaciers and small ice caps play a crucial role in freshwater availability. Widespread mass ... off the landscape to avoid floodingThe overflowing of the normal confines of a stream or other body of water, or the accumulation of water over areas that are not normally submerged. Floods include river (fluvial) floods, flash floods, urban floods, pluvial floods, sewer floods, coastal floods, and glacial lake outburst floods .... 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.

This makes managing urban watersheds a challenge. “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 waterDrinking water quality has a micro-biological and a physico-chemical dimension. There are thousands of parameters of water quality. In public water supply systems water should, at a minimum, be disinfected—most commonly through the use of chlorination or the use of ultra violet ..., recreation and aesthetic value.”

Given that dense urban neighborhoods don’t have a lot of space for nutrient-capturing features such as rainRain is liquid water in the form of droplets that have condensed from atmospheric water vapor and then precipitated—that is, become heavy enough to fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It ... gardens and ponds, the researchers point to alternate solutions such as focusing on reducing excessive nitrogen fertilizer use and keeping phosphorus out of streets and gutters in the first place, for instance by controlling erosion and increasing street sweeping efforts, and picking up dog waste as soon as possible to limit the release of phosphorus.

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Materials provided by University of Minnesota. Note: Content may be edited for style and length.

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