HR: 0800h
AN: H41D-0334    [Abstracts]
TI: Characteristics of the Nitrogen Cycle in Southern Everglades Marshes: 15N Tracer and Natural Abundance Experiments
AU: * Wozniak, J R
EM: wozniak@fiu.edu
AF: Florida International University / FCE LTER, University Park Campus, Miami, FL 33199 United States
AU: Anderson, W T
EM: andersow@fiu.edu
AF: Florida International University / FCE LTER, University Park Campus, Miami, FL 33199 United States
AU: Childers, D L
EM: chlders@fiu.edu
AF: Florida International University / FCE LTER, University Park Campus, Miami, FL 33199 United States
AU: Madden, C J
EM: cmadden@sfwmd.gov
AF: South Florida Water Managment District, Gun Club Road, West Palm Beach, FL 33406 United States
AU: Rudnick, D
EM: drudnic@sfwmd.gov
AF: South Florida Water Managment District, Gun Club Road, West Palm Beach, FL 33406 United States
AB: An {\it in situ} mesocosm experiment was conducted in the freshwater marshes of the Southern Everglades. The object of this experiment was to compare 15N natural abundances to N-cycling in mesocosms amended with 15N tracer. The 15N tracer technique allowed us to isolate the flows of N among various ecosystem components. Six mesocosms (2 m$^{2}$) were deployed in the oligotrophic P-limited marshes of the C-111 basin. The experiment ran for a period of 21 days with sampling occurring at t=0, 5, 10, 20, 30min, 1, 3, and 6hr on the first day and subsequently on days 2, 3, 5, 9, 15, and 21. Periphyton, soil, macrophytes ({\it Cladium jamaicense}), and consumers ({\it Gambusia holbrooki}) were collected. The isotopic tracer added to the enriched mesocosms possessed a \delta 15N value of 300\permil. Isotopic analysis was completed on a Finnigan Delta C EA-IRMS. All ecosystem components showed tracer uptake except for the soil, which remained at natural abundance levels throughout the experiment. Periphyton showed both the most rapid and the greatest N tracer uptake with an increase of 8.7\permil, 5 minutes after tracer addition and a maximum \delta 15N value of 197.93\permil at day 3. This experiment demonstrated that at study sites with low nitrate concentrations (\approx3\muM) a 300 permil dosing rate of 15N labled Ca(NO$_{3}$)$_{2}$ (\+98% 15N) would not increase mesocosm nitrate above ambient concentrations and would provide a significant isotopic signal to track fluxes of N among ecosystem components. In addition, an experiment was conducted in the same region to determine natural abundance values for ecosystem components at both near-canal and downstream sites. All components sampled at the near-canal site had significantly heavier nitrogen isotopic values than did the downstream components (\delta 15N 7.44\permil \pm2.11 and 2.01\permil \pm1.44 respectively); suggesting the Southern Everglades marsh is acting as a sink for canal-borne DIN and a source for "new" marsh derived DON.
DE: 1803 Anthropogenic effects
DE: 1871 Surface water quality
DE: 1040 Isotopic composition/chemistry
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting