Nitrogen Pollution Moving Through Forests Faster Than Expected

Research Issue

Forest stream. Photo credit: Stephen Sebestyen, USDA Forest Service.

For the most part, forests have been thought to be effective filters of nitrogen, with various organisms (aboveground vegetation, underground root systems, microbes, and fungi) reducing the amount of many pollutants that would otherwise reach lakes, rivers, and streams. However, in one of the largest and longest running studies of its kind, researchers are discovering that under certain circumstances, nitrate (a form of nitrogen) moves through landscapes too quickly for forests to be as effective, allowing pollutants to pass into headwater streams.

Our Research

An international cadre of researchers from academic institutions and government agencies, led by a Northern Research Station scientist, analyzed more than 1,800 water samples and monitoring data spanning 21 years across 13 states and the Canadian province of Ontario. Researchers looked for the presence of chemical tracers (isotopes of nitrate) that are unique to nitrate deposited through precipitation, such as rainfall and snowfall. The researchers discovered that the nitrate from precipitation was found more widely and more frequently in waterbodies than commonly recognized.

Expected Outcomes

Usually, forested landscapes are able to absorb the nitrate from precipitation. However, after some periods of rain or snowmelt, up to 60 percent of nitrogen found within the waterbody could be traced to that deposited through precipitation.
Scientists hypothesize that during these events, nitrate from precipitation passes through the landscape too quickly for vegetation and microbes to absorb, allowing more nitrate to drain into waterbodies.
Spikes in nitrate concentrations in headwater streams isn’t a novel concept. However, this latest research demonstrates it may be occurring more frequently and across more forests than previously thought. Furthermore, the volume of data collected is allowing researchers to identify patterns in soil properties, topography, vegetation, and weather to better anticipate where and when such occurrences are more likely.

Research Results

Sebestyen, Stephen D.; Ross, Donald S.; Shanley, James B.; Elliott, Emily M.; Kendall, Carol; Campbell, John L.; Dail, D. Bryan; Fernandez, Ivan J.; Goodale, Christine L.; Lawrence, Gregory B.; Lovett, Gary M.; McHale, Patrick J.; Mitchell, Myron J.; Nelson, Sarah J.; Shattuck, Michelle D.; Wickman, Trent R.; Barnes, Rebecca T.; Bostic, Joel T.; Buda, Anthony R.; Burns, Douglas A.; Eshleman, Keith N.; Finlay, Jacques C.; Nelson, David M.; Ohte, Nobuhito; Pardo, Linda H.; Rose, Lucy A.; Sabo, Robert D.; Schiff, Sherry L.; Spoelstra, John; Williard, Karl W. J. 2019. Unprocessed Atmospheric Nitrate in Waters of the Northern Forest Region in the U.S. and Canada. Environmental Science & Technology. 53(7): 3620-3633.

Research Participants

Principal Investigator

  • Stephen Sebestyen, USDA Forest Service Northern Research Station, Research Hydrologist

Research Partners

  • Last modified: December 7, 2020