Spectral characteristics of optically active constituents (OACs) in waters are key parameters of biooptical modeling. Comparative analyses about the differences of optical characteristics and composition between riverine and reservoir waters in the second Songhuajiang River tributaries were conducted, and the influencing factors impacting on chromophoric dissolved organic matter (CDOM) and organic carbon (DOC) were examined based on the absorption properties. Dissolved organic carbon (DOC) and total suspended matter (TSM) were significantly higher in the riverine waters, and chlorophyll-a (Chl-a) was opposite. The relationship between the CDOM absorption coefficient at specific wavelength and DOC concentration both in the riverine and reservoir waters exhibited a positive correlation (r = 0.90, p< 0.01). The close relationship between Chl-a concentration and CDOM absorption confirmed a small amount of phytoplankton absorption to total absorption in the individual samplings. Analysis of absorption ratio (E250:365), specific UV absorbance (SUVA254), and spectral slope ratio (Sr) indicated that CDOM in riverine waters had lower aromaricity, molecular weight, and vascular plant contributions than in reservoir waters. Furthermore, non-algal particles played an important role in the total non-water absorption for riverine waters, and CDOM was dominant in the reservoir waters. This indicated that the Yinma River watershed was strongly influenced by the artificial discharge. As a parameter of the bio-optical model, the spectral characteristics of CDOM could help to adjust derived algorithms based on remote sensing and to estimate the dissolved organic carbon flux.
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