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 Lehmann et al., 2005, Environ Poll

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

N-CYCLE IS COMPLICATED

Aber Spaghetti Diagram

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

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

DISSOLVED INORGANIC NITROGEN (DIN=NH NO 3 - ) 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

Perturbation: permafrost melting which is increasing N mineralization

PROMISING TOOL Potential Problems Biome differences Year-to-year and site-to-site differences Climate change

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

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

Questions?

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

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

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