This review has highlighted some of the recent results of investigations into the ecological photochemistry of CDOM. While much information continues to accumulate on this subject, several issues remain. One issue is the relative contribution of CDOM photomineralization to atmospheric C02 flux out of natural waters. Another issue is the role of CDOM photodegradation in the transport of terrestrial C to the coastal ocean and its effectiveness relative to microbial degradation. Furthermore, it is unknown how the importance of CDOM photodegradation in controlling water column transparency varies among different types of natural waters and with latitude. While action spectra and SWFs are useful, we do not know if a general model can be used for all types of CDOM - we need more information on factors that affect spectral weights. For example, does prior solar radiation exposure affect the calculation of spectral weights [132]? How do spectral weights calculated for marine vs. fresh water differ? Answers to these questions are required to accurately model CDOM changes in the natural environment. Although variation exists in the approaches used to isolate CDOM and model its photochemistry, this exciting field continues to grow as a large component of biogeochemical study. Further research should vastly improve our understanding of the role of CDOM in biogeochemical cycling and water column transparency.

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