240 likes | 321 Views
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.
E N D
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
NADP: NITRATE PERCENT CHANGE Lehmann et al., 2005, Environ Poll
NADP: AMMONIUM PERCENT CHANGE Lehmann et al., 2005, Environ Poll
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
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=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
Perturbation: permafrost melting which is increasing N mineralization
PROMISING TOOLPotential 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
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