Optical characterization of chromophoric dissolved organic matter using wavelength distribution of absorption spectral slopes

We use a new approach to characterize the absorption characteristics of chromophoric dissolved organic matter (CDOM) in standard solutions and in several tropical lake ecosystems (Lake Victoria, Lake Tanganyika, Laguna Ibera´ ). Compared with the common methods where a single slope of CDOM absorption spectrum is determined over a broad spectral region, we estimate the variations in spectral slope as a function of wavelength from 200 to 700 nm. Hence, our results show a distribution of spectral slope, referred to as the spectral slope curve, Sl, which was used to identify similarities between lakes and standard solutions as well as to show the wavelength intervals in which photodegradation modifies spectral slope. In contrast to the plethora of wavelength intervals and ratios presented in the CDOM literature, a comparison of spectral slope curves between ecosystems provides a potentially important tool to examine the characteristics of CDOM in a consistent manner.