Spectral absorption and fluorescence of chromophoric dissolved organic matter in shallow lakes in the middle and lower reaches of the Yangtze River

The optical properties of chromophoric dissolved organic matter (CDOM) in shallow lakes in the middle and lower reaches of the Yangtze River were investigated. Concentrations of dissolved organic carbon (DOC) ranged from 2.7 to 10.1 mg/L with an average of 5.65 +/- 1.70 mg/L. All spectra of CDOM had a common shape with maximal absorption in shorter wavelength and minimal absorption in longer wavelength. CDOM absorption coefficients at 280 nm and 355 nm were in the range 3.52-24.22 m(-1) (aver. age 8.69 +/- 4.76 m(-1)) and 0.53-8.08 m(-1) (average 2.03 +/- 1.65 m(-1)), respectively. The values of the DOC-specific absorption coefficient at 355 nm ranged from 0.09 to 0.80 L(mg org.C)(-1) m(-1). The exponential slope coefficient ranged from 0.015 to 0.023 nm(-1) with a mean value 0.020 +/- 0.002 nm(-1) over the 280-400 nm interval. Fluorescence emission at 450 nm, excited at 355 rim, had a mean value of 0.86 nm(-1). CDOM fluorescence and absorption, were significantly and positively correlated. The coefficient of variation between CDOM absorption and DOC concentration decreased with the increase of wavelength from 280 to 800 nm. The CDOM absorption measurements are of use to study regional distribution of CDOM, contribution of CDOM to light attenuation, and development of regional models for the optical properties of CDOM which allow higher precision in remote sensing applications of water quality monitoring.