Sunlight effects on diel CO2 and CH4 emissions from a tropical reservoir

eurrent studies show that reservoirs are responsible for emissions of greenhouse gases (ST. Loms et al. 2000, DucHEMIN et al. 2002, SouMIS et al. 2004, ABRIL et al. 2005, LIMA et al. 2008). Surface waters of aquatic ecosystems exhibit supersaturated dissolved e02 (CüLE 1999, RICHEY et al. 2002) because respiration based on both autochthonous and allocthonous organic carbon usually exceeds primary production (DEL GIORGIO et al. 1997, CoLE 1999, JoNssoN et al. 2003). Dissolved organic carbon transported to the aquatic ecosystem from the drainage basin usually remains bio1ogically refractory. Upon exposure to sunlight in a relatively well-lit aquatic environment, however, terrigenous organic carbon might undergo photolytic degradation and become more labile (CoLE 1999). In spite ofphotominemlization, carbon dioxide effiuxes may also result from methanotrophic activities (FRENZEL et al. 1990, ABE et al. 2005, LIMA 2005) associated with diel oxygen production via photosynthesis (KING 1990, LIMA et al. 2005a). Moreover, diel changes in sunlight may also affect dissolved gas solubility and, in particular, surface water density, leading to convection during cooling events (MAclNTYRE et al. 2001). We evaluated possible ro les of sunlight on the daily variability of eH4 and eo2 diffusive fluxes from eorumbá reservoir in Brazíl. Our results support that eo2 and eH4 emissions in eorumbá are substantially influenced by sunlightinduced processes, although we cannot precisely identify the primary variables inducing diel changes.