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Tracing Atmospheric Nitrate Deposition in a Complex Semiarid Ecosystem Using D 17 O

Tracing Atmospheric Nitrate Deposition in a Complex Semiarid Ecosystem Using D 17 O. by Michalski, G., Meixner, T., Fenn, M., Hernandez, L., Sirulnik, A., Allen, E., and Thiemens, M. Ranges of d 15 N and d 18 O values of different sources of NO 3 (from Kendall et al., 1998).

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Tracing Atmospheric Nitrate Deposition in a Complex Semiarid Ecosystem Using D 17 O

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  1. Tracing Atmospheric Nitrate Deposition in a Complex Semiarid Ecosystem Using D17O by Michalski, G., Meixner, T., Fenn, M., Hernandez, L., Sirulnik, A., Allen, E., and Thiemens, M.

  2. Ranges of d15N and d18O values of different sources of NO3 (from Kendall et al., 1998)

  3. Background-mass dependent vs. mass independent fractionation • Mass dependent fractionation that can alter d18O values will not affect the value of D17O. • Photochemical systems do not always follow the mass-dependent relationship for d17O • D17O signal is generated during the formation of ozone. • D17O is NOT affected by terrestrial fractionating processes (ie. nitrate transformation) • D17O more sensitive tracer for atmospheric nitrate than d18O measurements!!!

  4. Relationship between d18O and d17O values. Modified from Michalski et al., 2002.

  5. Mass Independent Fractionation • D17O = d17O -0.52 * d18O Nitrate with D17O > 0 o/oo is atmospheric D17O up to 31 permil for aerosols and rainwater (Michalski and Thiemens, 2000) D17O = 0 for fertilizer and bacterial nitrate

  6. Objectives of the study by Michalski and others (2004) Use D17O to quantify atmospheric nitrate in soils and streams compared with d18O techniques. Use results for process level understanding of fate and transport of nitrogen in the soil and catchment.

  7. N Dep = 35-45 kg/ha/yr N Study Area: Southern California N Dep = 5 kg/ha/yr N

  8. Oxygen Isotopic Composition of Stream and Soil NO3. (From Michalski et al., 2004)

  9. Oxygen three isotope plot of nitrate (from Michalski et al., 2004)

  10. NO3 from stream (o) and soil ( ) samples and d18O and mass balance mixing lines between atmospheric NO3 and nitrification NO3 (from Michalski et al., 2004).

  11. Mass balance estimates of the % of atmospheric NO3 in terrestrial NO3 (from Michalski et al., 2004)

  12. Streamflow hydrograph during Nov and Mar in Devil Canyon Watershed. (Michalski et al., 2004)

  13. Conclusions • D17O can be used as a conserved tracer • 4-40% unassimilated atmospheric nitrate in runoff (all sites) and 20-40% (Devils Canyon) • More robust indicator than d18O • Previous work may be underestimating atmospheric nitrate • Powerful new technique to augment the dual isotope technique

  14. Future Work with D17O • Kendall et al., in progress Analyzing D17O, d18O and d15N of nitrate from NADP for source identification. • Nanus et al., in progress Analyzing D17O, d18O and d15N of nitrate in alpine lakes in 5 Rocky Mountain National Parks. Compare to Kendall et al.

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