Fauchot, J. Université du Québec à Rimouski, juliette_fauchot@uqar.uquebec.ca
Gosselin, M. Université du Québec à Rimouski, Michel_Gosselin@uqar.uquebec.ca
Levasseur, M. Institut Maurice-Lamontagne, levasseurm@dfo-mpo.gc.ca
Mostajir, B. INRS-Océanologie, behzad_mostajir@uqar.uquebec.ca
Belzile, C. INRS-Océanologie,
Demers, S. INRS-Océanologie, serge_demers@uqar.uquebec.ca
Zulema Villegas, P. Université du Québec à Rimouski,

 
INFLUENCE OF UV-B RADIATION ON NITROGEN UTILIZATION BY A NATURAL ASSEMBLAGE OF PHYTOPLANKTON
 
A 7-day mesocosm experiment was conducted in July 1996 to investigate the effects of ambient UVBR exclusion and two UVBR enhancements above ambient levels on nitrate, ammonium and urea utilization by a natural phytoplankton community. Our study presents the first evidence that UVBR can influence phytoplankton urea uptake. The community was dominated by diatoms during the first three days and, afterwards, by flagellates and dinoflagellates. The results of 4h incubations at the mesocosm surface show that the exclusion of ambient UVBR at temperate latitudes can cause an increase in nitrate, ammonium and urea uptakes. During the last four days, the percent increase in urea uptake was even a linear function of the ambient UVBR dose removed. During the post-diatom bloom, UVBR enhancements resulted in decreases in nitrate, ammonium and urea uptakes compared to ambient UVBR conditions. The reduction of urea uptake under UVBR enhancements, during the last three days, was linearly related to the enhanced UVBR dose. Our results indicate that the effects of UVBR on nitrogen uptake change rapidly and depend on the species composition of the phytoplankton community, the time of the day and the light history of the cells.
 
Day: Thursday, Feb. 4
Time: 04:30 - 04:45pm
Location: Hilton of Santa Fe
 
Code: SS51TH0430E