Unprocessed atmospheric nitrate in waters of the northern forest region in the USA and Canada

Authors: SEBESTYEN, STEPHEN - Forest Service (FS); ROSS, DONALD - University Of Vermont; SHANLEY, JAMIE - Us Geological Survey (USGS); ELLIOTT, EMILY - University Of Pittsburgh; KENDALL, CAROL - Us Geological Survey (USGS); CAMPBELL, JOHN - Forest Service (FS); DAIL, BRYAN - University Of Maine; FERNANDEZ, IVAN - University Of Maine; GOODALE, CHRISTINE - Cornell University; LAWRENCE, GREGORY - Us Geological Survey (USGS); LOVETT, GARY - Cary Institute Of Ecosystem Studies; MCHALE, PATRICK - State University Of New York- College Of Environmental Science And Forestry; MITCHELL, MYRON - State University Of New York- College Of Environmental Science And Forestry; NELSON, SARAH - University Of Maine; SHATTUCK, MICHELLE - University Of New Hampshire; WICKMAN, TRENT - Forest Service (FS); BARNES, REBECCA - Colorado College; BOSTIC, JOEL - University Of Maryland; Buda, Anthony; BURNS, DOUGLAS - Us Geological Survey (USGS); ESHLEMAN, KEITH - University Of Maryland; FINLAY, JACQUES - University Of Minnesota; NELSON, DAVID - University Of Maryland; OHTE, NOBUHITO - Kyoto University; PARDO, LINDA - Forest Service (FS); ROSE, LUCY - University Of Minnesota; SABO, ROBERT - University Of Maryland; SCHIFF, SHERRY - University Of Waterloo; SPOELSTRA, JOHN - Consultant; WILLIARD, KARL - Southern Illinois University

Submitted to: Journal of Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2019
Publication Date: 3/4/2019
Citation: Sebestyen, S.D., Ross, D.S., Shanley, J.B., Elliott, E.M., Kendall, C., Campbell, J.L., Dail, B., Fernandez, I.J., Goodale, C.L., Lawrence, G.B., Lovett, G.M., McHale, P.J., Mitchell, M.J., Nelson, S.J., Shattuck, M.D., Wickman, T.R., Barnes, R.T., Bostic, J.T., Buda, A.R., Burns, D.A., Eshleman, K.N., Finlay, J.C., Nelson, D.M., Ohte, N., Pardo, L.H., Rose, L.A., Sabo, R.D., Schiff, S.L., Spoelstra, J., Williard, K.W. 2019. Unprocessed atmospheric nitrate in waters of the northern forest region in the USA and Canada. Journal of Environmental Science and Technology. 53:3620-3633. https://doi.org/10.1021/acs.est.9b01276.
DOI: https://doi.org/10.1021/acs.est.9b01276

Interpretive Summary: The deposition of atmospheric nitrate in rain and snow represents a significant source of nitrate pollution to watersheds across the Northern Forest Region of the continental US. In this study, we synthesized chemical and isotopic data across thirty-three forested watersheds to determine the proportion of atmospheric nitrate delivered to streams without biological processing. Results showed that the largest fractions of unprocessed atmospheric nitrate in stream water occurred during storms when near-stream saturated areas were hydrologically connected to surface waters. Findings from the study provide insight into the efficacy of ongoing efforts to mitigate the effects of atmospheric nitrate pollution in forested watersheds.

Technical Abstract: Little is known about the regional extent and variability of nitrate from atmospheric deposition being transported to streams without biological processing in forests. We measured water chemistry and isotopic tracers of nitrate sources across the Northern Forest 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 five of 33 streams had high fractions (>20%) of unprocessed atmospheric nitrate during baseflow. Seventeen had high fractions during stormflow, which corresponded to large fractions in near-surface soil waters or groundwaters, but not deep groundwater. The remaining 11 streams occasionally had some (<20%) unprocessed atmospheric nitrate during stormflow or baseflow. Lack of observance may bias perceptions of occurrence of large fractions; large, sporadic events may continue to be cryptic due to atmospheric deposition variation among storms and a general lack of adequate monitoring for these inputs. Nonetheless, such information is critical to defining the size and trend of chronic nitrogen pollution effects as well as the efficacy of regulatory and management schemes intended to reduce pollution effects on forests and streams.