ABSTRACT
This chapter focuses on research in the photochemistry of naturally occurring organic matter. Distinction between isolated and unisolated organic matter will be made with the terms dissolved humic substances and dissolved organic matter (DOM), respectively. Accurate descriptions of the link between DOM photochemistry and the optical properties of natural waters present a dilemma. While the absorbance-fluorescent characteristics of DOM in natural waters might be used to predict photochemical reactivity of given water mass, those same photochemical processes will result in a fundamental change of the spectral quality and reactivity of DOM. In addition to energy released as fluorescence, the absorbance of sunlight by naturally occurring DOM generates a variety of photochemical transients. A strong correlation exists between the photochemical production of low-molecular weight carbonyl compounds and the photodegradation of DOM in natural waters. Hydrogen peroxide exhibits vertical distributions which closely follow density structure and may prove useful as a tracer of photic zone processes or atmospheric input.
