The optical characterization of chromophoric dissolved organic matter using the wavelength distribution of absorption spectral slopes.

We utilise a new approach to characterise the absorption characteristics of chromophoric dissolved organic matter (CDOM) in standard solutions and in several tropical lake ecosystems (Lake Victoria, Lake Tanganyika, Laguna Iberá). In contrast to the usual methods of presenting specific wavelength intervals, we estimate CDOM absorption spectral slopes for all wavelengths from 200 nm to 700 nm. The results show a distribution of spectral slope, referred to as the spectral slope curve, S. Using S, it was possible 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 from various environments in a consistent manner.