Photoreactions of dissolved organic matter can affect the oxidizing
capacity, nutrient dynamics, trace gas exchange and color of surface waters. 
This study focuses on factors that affect the photoreactions of the colored
dissolved organic matter (CDOM) in the Satilla River, a coastal river that
has high concentrations of dissolved organic carbon (DOC) (2.0 ± 0.2 mM C) 
and iron (12 ± 2 µM) in its freshwater reach.  Quantum yields for the photoproduction 
of dissolved inorganic carbon (DIC) and carbon monoxide (CO) from Satilla CDOM 
decreased exponentially in the 300 - 450 nm spectral region.  Photoreaction of 
the CDOM in sunlight caused a decrease in UV and visible absorbance that occurred
most rapidly in the UV-B (280 - 315 nm) region, indicating that CDOM photoreactions
can enhance exposure of aquatic organisms to DNA-damaging UV radiation.  The 
role of iron in the photooxidation was investigated by adding fluoride ions or 
deferoxamine mesylate (DFOM) to the water to form unreactive Fe3+ complexes,
thus inhibiting iron photoreduction and slowing CDOM photooxidation.  Using
this method, it was demonstrated that the photoformation of DIC, CO, and
NH4+ is strongly affected by iron catalysis in the Satilla River water.  Increasing the dioxygen 
content and lowering the pH accelerated the photoreaction of the CDOM.  CDOM 
photoreaction was accompanied by conversion of dissolved iron and carbon to 
particulate forms.  Such "photocoagulation" may contribute to the transport of 
iron and carbon from surface waters to sediments in sunlit, well-stratified
aquatic ecosystems.