Analysis of atmospheric inputs of nitrate to a temperate forest ecosystem from Δ17O isotope ratio measurements

• Published in: Geophysical research letters Vol. 38; no. 15
• Main Authors: Costa, A. W., Michalski, G., Schauer, A. J., Alexander, B., Steig, E. J., Shepson, P. B.
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01.08.2011; American Geophysical Union
• Subjects: cycling; Earth sciences; Earth, ocean, space; Exact sciences and technology; forest; inputs; nitrate; stable isotopes; United States; Michigan; atmosphere; stable isotopes; rainfall; Atmospheric fallout; Oxygen 17; atmospheric precipitation; isotope ratios; nitrogen; tracers; Isotopic composition; clouds; nitrates; North America; atmospheric deposits; forests; productivity; solution; ecosystems; soils; Anthropogenic factor
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2011GL047539

Determining the fate of atmospheric N deposited in forest ecosystems is essential to understanding the ecological impact of increased anthropogenic N deposition. We hypothesize that a significant fraction of soil nitrate (dry deposited HNO3 and wet deposited NO3−) in northern Michigan is derived from atmospheric deposition. To test this idea, soil, rainfall, and cloud water were sampled in a temperate forest in northern Lower Michigan. The fraction of the soil solution NO3− pool directly from atmospheric deposition was quantified using the natural isotopic tracer, Δ17O. Our results show that on average 9% of the soil solution NO3− is unprocessed (no microbial turnover) N derived directly from the atmosphere. This points to the potential importance of anthropogenic N deposition and contributes to the long‐standing need to improve our understanding of the impacts of atmospheric nitrogen processing and deposition on forest ecosystems and forest productivity. Key Points Mass independent fraction of nitrate is a very useful tool for our question Atmospheric nitrate deposition is highly significant for N‐limited forests