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What we learned about isotopes

What we learned about isotopes. Elizabeth Sulzman. Problem 1: Sources of nitrate in ground water. The ground water in your area exceeds the EPA standard of 10 ppm of nitrate. What nitrate sources are responsible?. 3 possible sources 2 isotopic signatures measured in sources and groundwater.

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What we learned about isotopes

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  1. What we learned about isotopes Elizabeth Sulzman

  2. Problem 1: Sources of nitrate in ground water The ground water in your area exceeds the EPA standard of 10 ppm of nitrate. What nitrate sources are responsible? 3 possible sources 2 isotopic signatures measured in sources and groundwater

  3. Problem 1: Sources of nitrate in ground water

  4. Problem 1: Sources of nitrate in ground water

  5. Problem 1: Sources of nitrate in ground water

  6. Problem 2 What is the isotopic composition of soil respiration from a 40-yr-old stand dominated by Douglas-fir in the Cascade mountains of central Oregon.

  7. Problem 2 What is the isotopic composition of soil respiration from a 40-yr-old stand dominated by Douglas-fir in the Cascade mountains of central Oregon. • Differences north / south slopes? • Spatial aggregation to watershed level • Small scale Keeling plots • Soils & Foliage • North & South facing slopes • At different elevations • Watershed level Keeling plot

  8. Keeling plots Keeling (1958) Cmix= Cbg+ Csource dmixCmix= dbgCbg+ dsourceCsource dmixCmix = dbgCbg + dsource (Cmix – Cbg) dmixCmix = (dbg- dsource)Cbg + dsourceCmix dmix = (dbg- dsource)Cbg / Cmix+ dsource dmix= (slope)*(1/Cmix)+ dsource

  9. Keeling plot: dmix = (slope)*(1/Cmix) + dsource Hypothesis: North facing slope has a more negative (lighter) isotopic signature due to: Lower water stress Lower temperature

  10. Isotopic signature soil respiration

  11. Isotopic signature soil respiration Difference in isotopic signatures between north and south facing slope not large enough ?

  12. Problem 3: Contributions of C3 and C4 to ecosystem respiration Miranda et al. 1997

  13. Problem 3: Contributions of C3 and C4 to ecosystem respiration Miranda et al. 1997

  14. Problem 3: Contributions of C3 and C4 to ecosystem respiration Miranda et al. 1997 Two source mixing model: 54 +/- 7 % of ecosystem respiration stems from C3 sources.

  15. On to radioactive isotopes …

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