Nav: Home

University of Minnesota study shows wetlands provide landscape-scale reduction in nitrate pollution

January 31, 2018

MINNEAPOLIS / ST. PAUL (01/29/2018) -- A study by University of Minnesota researchers provides new insights to demonstrate that multiple wetlands or 'wetland complexes' within a watershed are extremely effective at reducing harmful nitrate in rivers and streams. These wetlands can be up to five times more efficient per unit area at reducing nitrate than the best land-based nitrogen mitigation strategies.

The research was published today in the scientific journal Nature Geoscience. The research was led by researchers from the University of Minnesota College of Science and Engineering's St. Anthony Falls Laboratory and the University's College of Biological Sciences.

In agricultural regions like the United States Midwest, excess nitrate derived from crop fertilizer makes its way to rivers and streams through subsurface drainage systems and agricultural ditches. Once in streams and rivers, high nitrate concentrations can be harmful to ecosystems and human health. This includes impacts such as drinking water contamination and the Gulf of Mexico Dead Zone. Although the topic has been the focus of extensive research, little traction has been made toward effective strategies for nitrate reduction at the landscape scale.

In this study, researchers used water samples collected over a four-year period from more than 200 waterways within the intensively managed, 17,000-square-mile Minnesota River basin, coupled with geo-spatial information about land use in the watershed. They were able to isolate the effect of wetlands on stream and river nitrate concentrations within large watersheds.

Significant research findings include:
  • When stream flows are high, wetlands are five times more efficient per unit area at reducing nitrate than the best land-based conservation practices. Other common conservation practices are effective at lower flow conditions but overwhelmed with higher stream flows.

  • The arrangement of wetlands within a watershed is a key predictor of the magnitude of nitrate reduction. If wetlands intercept 100 percent of the drainage area, they are three times more effective at nitrate removal compared to interception of 50 percent of the drainage area.

  • Nitrate reduction due to ephemeral (temporary) wetlands, such as riparian floodplains and more geographically isolated wetlands (wetlands not connected to the river network by surface water), was measurable and was highest during high stream flows, when such features are hydrologically connected to surface water.

This last finding is of particular interest to the current policy debate over management and regulations that influence water quality in agricultural regions. While there is strong scientific consensus that small or temporary water bodies such as ephemeral wetlands play essential roles for improving water quality downstream, their legal status for protection under the Clean Water Act is uncertain. Court rulings expected in 2018 could have a large impact on how, and if, these water bodies are protected in years to come.

"We value what we can measure, so this is an important step forward in recognizing that as we lose wetlands, we also lose the significant benefits they provide in terms of pollution control," said Amy Hansen, research associate at the University of Minnesota St. Anthony Falls Laboratory and one of the lead authors of the study.

The contribution of small wetlands is also especially important for the future. Climate forecasts for the region predict increases in both precipitation frequency and magnitude--conditions under which this study found that wetlands play a measureable role in reducing riverine nitrate.

"Our work shows that wetland restoration could be one of the most effective methods for comprehensive improvement of water quality in the face of climate change and growing global demand for food," said study co-author Jacques Finlay, a professor in the University of Minnesota's Department of Ecology, Evolution and Behavior in the College of Biological Sciences.

The results of this research not only help to advance the science of wetlands and pollution control, but also can provide practical applications for practitioners looking to develop guidance on wetland restoration siting and potential benefits. By being able to target locations on the landscape where wetland restoration would be most effective for nitrate removal, more strategic alliances and funding may become available to make such projects happen.

"The location of the wetlands are important predictors of how effective they are at reducing nitrate," Hansen said. "Water quality programs that target these locations would be more cost effective as well."

Others agree that more wetlands could be a win-win locally and nationally.

"Agricultural productivity benefits the economy, but is often accompanied by environmental costs," said Tom Torgersen, director of the National Science Foundation (NSF)'s Water, Sustainability and Climate program that funded the research. "This study demonstrates that retaining or restoring wetlands in intensively managed agricultural watersheds would reduce nitrate in rivers and improve local water quality, while also reducing nitrate exports to the Gulf of Mexico hypoxic zone."
In addition to Hansen and Finlay, other authors of the study were Christy Dolph, University of Minnesota Department of Ecology, Evolution and Efi Foufoula-Georgiou, University of California, Irvine.

To read the full research paper entitled "Contribution of wetlands to nitrate removal at the watershed scale," visit Nature Geoscience.

University of Minnesota

Related Water Quality Articles:

Study quantifies effect of 'legacy phosphorus' in reduced water quality
For decades, phosphorous has accumulated in Wisconsin soils. Though farmers have taken steps to reduce the quantity of the agricultural nutrient applied to and running off their fields, a new study from the University of Wisconsin-Madison reveals that a 'legacy' of abundant soil phosphorus in the Yahara watershed of Southern Wisconsin has a large, direct and long-lasting impact on water quality.
New standards for better water quality in Europe
The European Water Framework Directive (WFD) is due to be revised by 2019.
Investigating the impact of 'legacy sediments' on water quality
University of Delaware researcher Shreeram Inamdar has been awarded a $499,500 grant from the US Department of Agriculture (USDA) to determine if stream-bank legacy sediments are significant sources of nutrients to surface waters and how they may influence microbial processes and nutrient cycling in aquatic ecosystems.
Adaptive management of soil conservation is essential to improving water quality
The quality of our rivers and lakes could be placed under pressure from harmful levels of soluble phosphorus, despite well-intended measures to reduce soil erosion and better manage and conserve farmland for crop production, a new study shows.
Big data approach to water quality applied at shale drilling sites
A computer program is diving deep into water quality data from Pennsylvania, helping scientists detect potential environmental impacts of Marcellus Shale gas drilling.
More Water Quality News and Water Quality Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#534 Bacteria are Coming for Your OJ
What makes breakfast, breakfast? Well, according to every movie and TV show we've ever seen, a big glass of orange juice is basically required. But our morning grapefruit might be in danger. Why? Citrus greening, a bacteria carried by a bug, has infected 90% of the citrus groves in Florida. It's coming for your OJ. We'll talk with University of Maryland plant virologist Anne Simon about ways to stop the citrus killer, and with science writer and journalist Maryn McKenna about why throwing antibiotics at the problem is probably not the solution. Related links: A Review of the Citrus Greening...