CS36 Ultraviolet Radiation
Date: Friday, June 14, 2002
Time: 8:45:00 AM
Location: Sidney
 
FrenetteJJ, Université du Québec à Trois-Rivières, Trois-Rivières, Canada, Jean-Jacques_Frenette@uqtr.ca
Arts, M, T, National Water Research Institute, Environment Canada, Burlington, Canada, Michael.Arts@ec.gc.ca
Daoust, B, , Université du Québec à Trois-Rivières, Trois-Rivières, Canada, Benoit_Daoust@uqtr.ca
 
BIO-OPTICAL VARIABILITY IN A FLUVIAL LAKE: EVIDENCE OF HIGHER PRODUCTIVITY WITH INCREASED UV PENETRATION
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Lake Saint-Pierre is the largest (480 km2) and most productive fluvial lake in the St. Lawrence River system. This lake exhibits high bio-optical variability within its three distinct water masses (north, central and south). We speculate that this increased physical complexity contributes to the high biodiversity of this lake. For example, the south water mass is more heterogeneous and productive than the north water mass as demonstrated by its higher fish densities and growth rates. However, in an apparent contradiction, detailed light measurements revealed a deeper penetration of ultraviolet radiation (UVR) and PAR in the south versus the north water mass. We demonstrate that the penetration UVR and blue light is controlled by CDOM absorption as well as suspended organic and inorganic particles. The south water mass had higher concentrations of fulvic acids and aliphatic molecules suggesting a greater presence of smaller, more autochthonously-derived, material. Thus, we suggest that the UV penetration depth and residence time, through their combined effects on photodecomposition of DOM, may have important implications for ecosystem productivity; especially for fluvial lakes bordered by wetlands.