Cabana, G. University of California at Berkeley, gcabana@socrates.berkeley.edu
Rainey, W. University of California at Berkeley, wrainey@socrates.berkeley.edu
Finlay, J. University of California at Berkeley, jfinlay@socrates.berkeley.edu
Power, M. University of California at Berkeley, mepower@socrates.berkeley.edu
Kendall, C. USGS, ckendall@usgs.gov
Schmitt, C. USGS Midwest Science Center, Christopher_Schmitt@usgs.gov

 
NITROGEN ISOTOPE RATIOS: INDICATORS OF SOURCE OF N OR N TRANSFORMATIONS?
 
The high nitrogen isotopic ratios of sewage-derived N has been proposed as a useful tracer of the incorporation of N from human and animal wastes into aquatic food webs. However, other studies have shown that fractionation associated with gaseous losses (denitrification, volatilization) from high N-inputs system , can also lead to high delN15 . Thus, delN15 may be an indicator of nitrogen losses from systems under high loadings rather than a tracer of the ultimate source of N. We investigated the relations among land use, total nitrogen concentration in the water, and the delN15 in 61 riverine locations within the U.S., using invertebrate-feeding fish collected as part of the National Contaminant Biomonitoring Program (NCBP). Fish delN15 , (+4 to +18 %o ) , was significantly (P<0.01) related to TN in the water and the percent of the watershed exploited as urbanization and agriculture. However, high delN15 values were observed in watersheds dominated by agriculture as well as ones dominated by urbanization. Thus delN15 may not be an indicator of the source of nitrogen (fertilizer vs sewage), but instead an indicator of the extent of N-fractionating processes in ecosystems impacted by excess nitrogen loadings.
 
Day: Wednesday, Feb. 3
Time: 09:15 - 09:30am
Location: Eldorado Hotel
 
Code: SS32WE0915E