Water is a precious resource, one that plays an important role in everything from public health and environment to agriculture and economics and is vital to sustaining life on Earth.
One of the major challenges threatening our waterways today is a phenomenon known as nutrient pollution. Nitrogen and phosphorus, nutrients that are a natural part of aquatic ecosystems like streams and rivers, can have lasting impacts on the environment and public health when their concentrations exceed certain thresholds.
In a new study published in Ecological Applications, researchers analyzed data to better understand nutrient transport in streams and rivers across the United States.
David Manning, assistant professor of biology at the University of Nebraska at Omaha and lead author on the paper, says the findings suggest most U.S. streams and rivers have higher levels of nitrogen and phosphorus than is recommended for protecting ecological integrity.
“High concentrations of nitrogen and phosphorus in our waterways are concerning because they threaten both human and ecosystem health,” Manning says. “Nutrients are essential for all life, but when they get too high in our waterways, they can fundamentally change the way a stream looks and operates.”
High concentrations of nitrogen and phosphorus in our waterways are concerning because they threaten both human and ecosystem health.
- David Manning, Assistant Professor of Biology at UNO
These elevated nutrient concentrations can lead to a lack of species diversity, oxygen depletion, and algal blooms, large growths of algae that overwhelm the ecosystem and harm habitats and water quality, threaten fish and insect communities, and even produce toxins that are harmful to humans.
High nutrient concentrations can also affect the purity of the water we drink. Here in Omaha, more than half the drinking water comes from small streams similar to the ones analyzed in the study. Nationwide, more than a third of the population relies on drinking water sourced from small streams.
The study found that even minor amounts of human activity can increase nutrient concentrations in freshwater sources. Higher concentrations of nitrogen are more likely to come from transportation, industry, agriculture and fertilizer application, while increased phosphorus is more commonly the result of sewage waste, amplified soil erosion and runoff from urban watersheds.
Concentrations of both nitrogen and phosphorus were higher in streams and rivers with more agricultural and urban land cover as opposed to forested land cover.
“The consequences of our actions that affect the small streams flowing through our cities, like Omaha, eventually affect larger rivers, such as the Missouri, before finally reaching the coast,” Manning says. “Because of this upstream-downstream connection, smaller streams serve as a first line of defense between a nutrient source, and its potential trip downstream.”
Nutrient pollution is a complex problem. While there’s still a lot of work to be done to develop management tools and set thresholds for nutrient concentrations in streams and rivers, better understanding of how nutrients are transported through the interconnected network of waterways can help lead to solutions.
And there are some actions that could be implemented today.
“We all live close to headwater streams, and so we can all play a role in promoting the health of streams in our backyard,” Manning says. “Some steps to take might include rethinking how much and how often we apply fertilizers, picking up pet wastes (a potential source of phosphorus), and supporting new, creative stormwater management infrastructure, including green infrastructure.”