Optical absorption and fluorescence properties of chromophoric dissolved organic matter in natural waters

Abstract

Complete optical absorption and fluorescence spectra were collected for a diverse suite of 0.2‐µm‐filtered marine, riverine, and estuarine waters, as well as for colored dissolved organic matter (CDOM) isolated from several of these waters by solid‐phase C18 extraction. Absorption and fluorescence parameters for these samples arc reported. For surface waters, variations in the fluorescence quantum yields obtained with 355‐ and 337‐nm excitation fell within a narrow window (<2.5‐fold variation about the mean values), demonstrating that fluorescence measurements can be used to determine absorption coefficients of CDOM in the ultraviolet region with reasonably good accuracy. Methods for predicting absorption coefficients and line shapes from the fluorescence data are introduced and tested. The absorption and fluorescence spectra of CDOM extracted from some seawaters differed significantly from those of the original waters, demonstrating that material isolated by hydrophobic adsorption is not necessarily representative of the suite of colored organic matter present in aquatic systems. These results clearly illustrate that great care must be taken when extracted material is used to infer the optical properties of natural waters.