Photochemistry of natural dissolved organic matter in lake and wetland waters—production of carbon monoxide

The photochemical formation of carbon monoxide (CO) in various lake and wetland waters was found to be correlated with the concentration of dissolved organic carbon (DOC), as well as light absorbance and fluorescence of the waters, suggesting that dissolved organic matter is a major precursor for CO photoproduction. Rates of CO formation also increased nonlinearly with increasing concentration of dissolved iron. For the lake and wetland waters studied, CO production rates were between 13 and 910 nmol 1−1 h−1 using June solar noon sunlight irradiations. Field experiments in a subtropical pond demonstrated that much of photochemically formed CO in the surface water was effluxed to the atmosphere. Considering the globally-averaged effective sunlight flux, we estimate that photoformation of CO leads to a turnover time of 2–10 yr for DOC in sunlit surface waters.