Characteristics, sources and driving factors of riverine CDOM in a severe erosion basin on the Loess Plateau, China

Abstract

Chromophoric dissolved organic matter (CDOM) plays a crucial role in aquatic ecosystems and biogeochemical processes. The characteristics, sources and influencing factors of riverine CDOM were determined with 56 samples collected in the Wuding River (WDR) Basin in spring and summer. The CDOM optical characteristics varied greatly during different seasons. The mean S275-295 was higher in spring than in summer, while SUVA254 exhibited the opposite result. The mean biological source index (BIX) was lower in summer than in spring, while the mean humification index (HIX) was higher in summer than in spring (p < 0.01). C1 and C3 (humic-like components) and C2 (tryptophan-like component) were extracted by parallel factor analysis (PARAFAC). C1 and C3 were prominent in summer, while C2 was prominent in spring. The effects of environmental factors on CDOM showed great differences. Chlorophyll a (Chla), dissolved organic carbon (DOC), electrical conductivity (EC) and dissolved oxygen (DO) had significant effects on the CDOM concentration (p < 0.05) in spring, while only DOC exerted significant effects on the CDOM concentration in summer. However, water quality parameters played important roles in evaluating the CDOM fluorescence components in summer. Total suspended matter (TSM) and turbidity (Tur) exerted significant effects on the humic-like fluorescence peaks (p < 0.05), while pH, Chla, DO, and EC had significant influences on tryptophan-like substances during this period. Based on redundancy analysis, precipitation, water erosion area and human activity intensity greatly affected the CDOM concentration, C1 and C3, while human activity intensity significantly affected C2 in the sub-basins in summer. CDOM was not significantly influenced by the surrounding environmental factors in spring except for the human activity intensity, which greatly influenced C1 and C3.