Unprocessed Atmospheric Nitrate in Waters of the Northern Forest Region in the U.S. and Canada
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Environmental Science & Technology
Little is known about the regional extent and variability of nitrate from atmospheric deposition that is transported to streams without biological processing in forests. We measured water chemistry and isotopic tracers (δ18O and δ15N) of nitrate sources across the Northern Forest Region of the USA and Canada and reanalyzed data from other studies to determine when, where, and how unprocessed atmospheric nitrate was transported in catchments. These inputs were more widespread and numerous than commonly recognized, but with high spatial and temporal variability. Only six of 32 streams had high fractions (>20%) of unprocessed atmospheric nitrate during baseflow. Seventeen had high fractions during stormflow or snowmelt, which corresponded to large fractions in near-surface soil waters or groundwaters, but not deep groundwater. The remaining ten streams occasionally had some (<20%) unprocessed atmospheric nitrate during stormflow or baseflow. Large, sporadic events may continue to be cryptic due to atmospheric deposition variation among storms and a near complete lack of monitoring for these events. A general lack of observance may bias perceptions of occurrence; sustained monitoring of chronic nitrogen pollution effects on forests with nitrate source apportionments may offer insights needed to advance the science as well as assess regulatory and management schemes.
Keywordsnitrogen deposition, nitrate isotopes, unprocessed nitrate from atmospheric deposition, Northern Forest Region of the USA and Canada, nitrogen-pollutant effects
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. https://doi.org/10.1021/acs.est.9b01276.