Articles | Volume 10, issue 6
Biogeosciences, 10, 3547–3558, 2013
Biogeosciences, 10, 3547–3558, 2013

Research article 03 Jun 2013

Research article | 03 Jun 2013

Tracing atmospheric nitrate in groundwater using triple oxygen isotopes: evaluation based on bottled drinking water

F. Nakagawa1, A. Suzuki1, S. Daita1, T. Ohyama2, D. D. Komatsu2, and U. Tsunogai2 F. Nakagawa et al.
  • 1Earth and Planetary System Science, Faculty of Science, Hokkaido University, N10 W8, Kita-ku, Sapporo, 060-0810, Japan
  • 2Graduate School of Environmental Studies, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan

Abstract. The stable isotopic compositions of nitrate dissolved in 49 brands of bottled drinking water collected worldwide were measured, to trace the fate of atmospheric nitrate (NO3 atm) that had been deposited into subaerial ecosystems, using the 17O anomalies (Δ17O) of nitrate as tracers. The use of bottled water enables collection of groundwater recharged at natural, background watersheds. The nitrate in groundwater had small Δ17O values ranging from −0.2‰ to +4.5‰ n = 49). The average Δ17O value and average mixing ratio of atmospheric nitrate to total nitrate in the groundwater samples were estimated to be 0.8‰ and 3.1%, respectively. These findings indicated that the majority of atmospheric nitrate had undergone biological processing before being exported from the surface ecosystem to the groundwater. Moreover, the concentrations of atmospheric nitrate were estimated to range from less than 0.1 μmol L−1 to 8.5 μmol L−1 with higher NO3atm concentrations being obtained for those recharged in rocky, arid or elevated areas with little vegetation and lower NO3atm concentrations being obtained for those recharged in forested areas with high levels of vegetation. Additionally, many of the NO3atm-depleted samples were characterized by elevated δ15N values of more than +10‰. Uptake by plants and/or microbes in forested soils subsequent to deposition and the progress of denitrification within groundwater likely plays a significant role in the removal of NO3atm.

Final-revised paper