China were examined to determine relationships between lake water sources (fresh versus saline) and their fluorescence/absorption characteristics. Results indicated significant differences regarding DOC concentration and a CDOM (254) between freshwater (6.68 mg C L-1 , 19.55 m-1) and saline lakes (27.4 mg C L-1 , 41.17 m-1). While humic-like (F 5) and fulvic-like (F 3) compounds contributed to CDOM fluorescence in all lake waters significantly, their contribution to total fluorescence intensity (F T) differed between saline and freshwater lakes. Significant negative relationships were also observed between lake altitude with either F 5 (R 2 =0.63, N=306) or F T (R 2 =0.64, N=306), suggesting that the abundance of humic-like materials in CDOM tends to decrease with increased in lakes altitude. In high-altitude lakes, strong solar irradiance and UV exposure may have induced photo-oxidation reactions resulting in decreased abundance of humic-like substances and the formation of low molecular weight compounds. These findings have important implications regarding our understanding of C dynamics in lacustrine systems and the contribution of these ecosystems to the global C cycle.

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