Tank, J. L. University of Illinois, jtank@uiuc.edu
Mulholland, P. J. Oak Ridge National Laboratory, jdn@ornl.gov
Bowden, W. B. Landcare Research, bowdenb@landcare.cri.nz
McDowell, W. University of New Hampshire, bill.mcdowell@unh.edu
Merriam, J. University of New Hampshire, jmerriam@hopper.unh.edu
Peterson, B. J. Ecosystems Center, peterson@lupine.mbl.edu
Meyer, J. L.
Webster, J. R. Virginia Tech, jwebster@vt.edu
Sanzone, D.

 
ASSESSING STORM EFFECTS ON NITROGEN CYCLING IN STREAMS USING 15N AS A TRACER
 
The effect of storms on nitrogen cycling was examined in 4 streams (Upper Ball Creek, NC, Walker Branch, TN, Bear Brook, NH, and Q. Bisley, PR) during 6-wk tracer additions of 15NH4. A storm that increased discharge 7-20 fold occurred at each site approximately 3 weeks into each experiment. Weekly sampling of food web compartments throughout the 6-week experiment indicated that despite the high discharges, there was less loss and replacement from upstream of benthic organic matter and organisms than we had predicted. Epilithon was not significantly scoured and del 15N values for epilithon increased after the storm in 3 of 4 streams. Significant flushing of pre-storm organic material and replacement by unlabeled material from upstream occurred in only one case (FBOM in QB). In WB, del 15N values for leaves and FBOM were always very low and decreased only slightly after the storm. In contrast, invertebrate consumers were not impacted by the relatively short-term (<24h) high flows, and their del 15N values were always similar or higher than pre-storm measurements. Results indicated that nitrogen cycling by both food resources and consumers seems to be relatively unimpacted by storms, and retention of organic matter in these streams is high.
 
Day: Wednesday, Feb. 3
Time: 02:30 - 02:45pm
Location: Eldorado Hotel
 
Code: CS64WE0230E