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A NOVEL INDICATOR OF ECOSYSTEM N STATUS: RATIO OF DIN TO DON IN ANNUAL RIVERINE FLUX

A NOVEL INDICATOR OF ECOSYSTEM N STATUS: RATIO OF DIN TO DON IN ANNUAL RIVERINE FLUX. Mark Williams, CU Boulder Dave Clow, USGS Tamara Blett, NPS. Global Problem: Increasing Nitrogen Deposition. NADP: NITRATE PERCENT CHANGE. Lehmann et al., 2005, Environ Poll. NADP: AMMONIUM PERCENT CHANGE.

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A NOVEL INDICATOR OF ECOSYSTEM N STATUS: RATIO OF DIN TO DON IN ANNUAL RIVERINE FLUX

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  1. A NOVEL INDICATOR OF ECOSYSTEM N STATUS: RATIO OF DIN TO DON IN ANNUAL RIVERINE FLUX Mark Williams, CU Boulder Dave Clow, USGS Tamara Blett, NPS

  2. Global Problem: Increasing Nitrogen Deposition

  3. NADP: NITRATE PERCENT CHANGE Lehmann et al., 2005, Environ Poll

  4. NADP: AMMONIUM PERCENT CHANGE Lehmann et al., 2005, Environ Poll

  5. NPS RESOURCE MANAGERS • In the hot seat • Need metrics • to evaluate • ecosystem N status • before we have dead • fish and dead trees • Simpler the better • Identify thresholds

  6. N-CYCLE IS COMPLICATED

  7. Aber Spaghetti Diagram

  8. DIN:DON RATIO IN ANNUAL DISCHARGE PROVIDES A METRIC FOR ECOSYSTEM NITROGEN STATUS

  9. DISSOLVED ORGANIC NITROGEN (DON) • Developed from soil organic nitrogen • Generally recalcitrant organic nitrogen • Not tasty to microbes • Companion to dissolved organic carbon (DOC) • Not generally measured • Difference of TDN minus DIN • Dominant form of N loss in pristine catchments

  10. DISSOLVED INORGANIC NITROGEN (DIN=NH4+ + NO3-) • DIN is the form of nitrogen used by plants and microbes • Microbes respond immediately to increased available DIN (fertilizer, atm) • DIN tightly recycled in N-limited ecosystems • DIN rarely in surface waters

  11. Perturbation: permafrost melting which is increasing N mineralization

  12. PROMISING TOOLPotential Problems • Biome differences • Year-to-year and site-to-site differences • Climate change

  13. Very wet year flushes out more nitrate. Non-linear response

  14. THE DIN and DON STORY • Shows promise as an indicator of ecosystem N status • Interannual and other variations need to be addressed • May provide a simple vital sign to resource managers

  15. Questions?

  16. HYPOTHESIS • DON export not related to N input • N deposition acclerates N mineralization • DIN increases much faster than DON • DIN:DON ratio metric for ecosystem N status

  17. DON DOES NOT RESPOND TO N ADDITIONS • LEAKY FAUCET HYPOTHESIS • Persistent “leak” of DON from catchments • DON is decoupled from microbial demand for N. • DON export coupled to soil standing stock of C, N • Lag between N inputs and DON export

  18. NITRATE LOSSES • Increasing N deposition increases net nitrification • Nitrate mobile • Nitrate export to surface waters increases as N deposition increases

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