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

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, Delta O-17. 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. Citation: Costa, A. W., G. Michalski, A. J. Schauer, B. Alexander, E. J. Steig, and P. B. Shepson (2011), Analysis of atmospheric inputs of nitrate to a temperate forest ecosystem from Delta O-17 isotope ratio measurements, Geophys. Res. Lett., 38, L15805, doi:10.1029/2011GL047539.