Investigating the Structural Basis of the Optical and Photochemical Properties of Chromophoric Dissolve Organic Matter

University Of Maryland, College Park, College Park MD

Investigators

Abstract

The importance of chromophoric dissolved organic matter (CDOM) to the aquatic light field and the biogeochemistry of both fresh and marine waters has been well established over the last 20 years; however, the structural basis of its optical and photochemical properties remain unclear, particularly for marine waters. Scientists from the University of Maryland will address this issue by a applying a comprehensive suite of optical, mass spectral, chemical, and photochemical measurements to samples (solid phase C-18 extracts and the original waters when possible) collected on a cruise transecting the equatorial Atlantic. Results from this study will be compared with those obtained from fresh, estuarine, and coastal waters of the Middle Atlantic Bight. The complete spectral dependencies of absorption and fluorescence emission will be acquired and compared with the lignin phenol content, the ultra-high resolution mass spectra, relative average size as determined by gel permeation chromatography, and dissolved organic carbon content. Two indices of photochemical reactivity, the photo-production of hydrogen peroxide and the photo-sensitized oxidation of selected phenols, will be further employed to examine how reactivity is affected by structural differences in CDOM collected from fresh, coastal and offshore waters. Changes in the optical spectra, ultra-high resolution mass spectra and photochemical reactivity following treatment with sodium borohydride, a selective reductant of aldehydes, ketones and quinones, will be used to test for the presence of charge-transfer interactions and their possible contribution to the optical properties, as well as to potentially establish unequivocal markers of CDOM source. In terms of broader impacts, this research would provide new insights on the structural basis for the optical and photochemical properties of chromophoric dissolved organic matter, as well as place constraints on the sources of this material. Two graduate students would be supported and trained as part of this project. It is anticipated that University of Maryland undergraduate students and French undergraduate students from the Engineering School of Chemistry of the Ecole Nationale Superieure de Chimie de Clermont Ferrand also would participate in the study but at no cost to the project.