HR: 14:40h
AN: H53F-05    [Abstracts]
TI: A Novel Indicator of Ecosystem N Status: DIN to DON Ratio in Riverine Waters
AU: * Williams, M W
EM: markw@snobear.colorado.edu
AF: INSTAAR and Department of Geography, University of Colorado, CB 450, Boulder, CO 80309
AU: Clow, D
EM: dwclow@usgs.gov
AF: USGS Water Resources Division, MS 415 Denver Federal Center, Lakewood, CO 80225
AU: Blett, T
EM: Tamara_Blett@nps.gov
AF: USDI-National Park Service Air Resources Division, Academy Place, Room 450 PO Box 25287, Denver, CO 80225
AB: We propose that the ratio of the annual flux of DIN to DON in streamwaters provides a robust and sensitive method of determining the N-status of ecosystems from a variety of biomes. Effects of N deposition are generally decoupled from N deposition because of the large variety of N species found in air, deposition, watersheds, and surface waters, as well as the myriad of pathways through which N can be cycled in terrestrial and aquatic ecosystems Moreover, the amount of N in biomass and soils and resident time within these reservoirs varies widely among biomes. Consequently, developing robust indicators of the N-status of ecosystems is difficult. Our results from many biomes suggest that N-limited ecosystems have DIN:DON ratios less than 0.5 and that ecosystems where N is no longer limiting have DIN:DON ratios greater than 2.0. The DIN:DON ratio in annual riverine yields is independent of ecosystem N storage, rates of N cycling, magnitude of N yield in surface waters, and hence a robust indicator of the N-status of ecosystems. We hypothesize that DON export from terrestrial ecosystems is controlled primarily by the standing stock of C and N in soils and hence will change only slowly in response to anthropogenic additions of N. In contrast, atmospheric deposition of N stimulates net nitrification and nitrate export in soil solution and stream waters. Therefore export of dissolved inorganic N responds directly and quickly to increases in anthropogenic deposition of N.
DE: 1806 Chemistry of fresh water
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting