The changes in the optics and chemistry of chromophoric dissolved organic matter (CDOM) caused by exposure to solar radiation (especially UVR) is an essential component of evaluating the effect of UVR on aquatic ecosystems. We briefly review photochemical concepts relevant to CDOM (light absorption in natural waters and photochemical reactions) and then describe methods for characterization of CDOM before considering the photochemical changes in CDOM and measurement of CDOM photoproducts. Experimental considerations necessary for working with polychromatic solar radiation are reviewed and briefly compared to monochromatic studies to provide a mechanism for predictive modeling of optical changes to CDOM based on measurements of solar radiation. CDOM sources, sinks, and transformations are discussed in context of UVR exposure in ecosystems and the cycling of carbon. Finally, we consider future directions of CDOM to include a more sophisticated connection between CDOM photodegradation and carbon cycling in aquatic ecosystems.

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