Optical Absorption Properties of Chromophoric Dissolvable Organic Matter (CDOM) and Their Quantitative Relationships With Dissolved Organic Carbon in the Poyang Lake in Dry Season

Optical absorption properties of chromophoric dissolvable organic matter (CDOM) in the waters of the Poyang Lake including estuaries and the main waterbody in the dry season of 2015 were studied and their relationships with dissolved organic carbon (DOC) discussed. Results show that CDOM absorption coefficient in the Poyang Lake at 254, 280, 350, and 440 nm (wave length) varied in the range of 7.86-20.24, 5.64-14.58, 1.46-4.41 and 0.36-1.06 m^-1, respectively, and M value, an index characterizing relative molecule size, did in the range from 5.27 to 7.66. During the dry season, wetlands were a major factor affecting CDOM concentrations in the lake, whereas the five major incoming rivers did not have much contribution to CDOM. Among the numerous parameters, S_R was the major index reflecting optical absorption properties of CDOM in the lake during the dry season. DOC in the dry season varied in the range from 1.61 to 4.86 mg·L^-1, with a mean value of 2.31 mg·L^-1. CDOM optical absorption coefficient(a₂₅₄,x) was positively related to DOC concentration (y). The relationship was fitted with the linear regression equation y=-0.53+0.27x and calibrated with the equation Adj. R²=0.76, P<0.01. Validation with the field measurements conducted in the Poyang Lake in January 2016 demonstrates that it is feasible to use optical absorption properties of CDOM in the waterbody of the Poyang Lake during the dry season to explore DOC concentration in the lake water, which means that CDOM in the Poyang Lake in the dry season can be used as an indicator in the study on carbon pool in the lake.