Alpine meadows and wetlands of western Sichuan plateau are essential organic carbon pools for Tibetan plateau; thus, a thorough understanding of the characteristics of dissolved organic carbon (DOC) and its association with soil carbon storage pool helps to reveal the flux and intensity of DOC export in the area. Surface water samples were collected from three rivers (the upper reaches of Min River, Zagunao River, and Fubian River) in the alpine-gorge region and Bai River in the plateau planation surface distributed among the watersheds in western Sichuan plateau, Southwest China. UV absorbance and EEM fluorescence spectroscopy with parallel factor analysis (PARAFAC) was used to characterize chromophoric dissolved organic matter (CDOM). PARAFAC produced a three-component model:C1(260/480) and C2(310/420) represented terrestrial humic-like fluorophores, and C3(280/370) belonged to tyrosine-like substances. The total fluorescence intensity of CDOM in the alpine-gorge region showed fewer changes along the rivers and was lower than that of the Bai River in the hilly plateau. The Bai River had much higher concentrations of humic-like substances (C1,C2) compared to the other three rivers, indicating its terrestrial sources with high humification degree originated from meadows and watersheds along the river. The calculated fluorescence indices (FI, BIX, HIX, β:α) showed that CDOM in the alpine-gorge region was a mixture with both autochthonous and allochthonous origins with low humification degree, while CDOM in the plateau planation surface had a higher degree of humification and lower extent of degradation. Statistical analysis showed that the C1 and C2 components in four rivers were significantly positively correlated, and C1, C2 and C3 components in Bai River were significantly positively correlated. β:α and BIX were significantly positively correlated in four rivers, but there was no significant correlation between DOC and CDOM[a(355)].
Keywords: EEM-PARAFAC; chromophoric dissolved organic matter (CDOM); natural waters; rivers in the western Sichuan plateau.