Assessing the photochemical mineralisation of dissolved organic carbon in lakes

Photochemical mineralisation is an abiotic process by which the organic matter in natural waters, which is mostly dissolved, is eventually transformed into CO2 by the action of sunlight. The process has important implications for global C cycling, the penetration of sunlight into the water column, photochemical reactions, and microbial processes. Here we applied an approximated photochemical model to assess the extent of CO2 photogeneration by mineralisation of dissolved organic matter in lakes located between 60°S and 60°N latitude. The results suggest that, although lake-water organic matter would usually undergo faster photomineralisation in the tropical belt than elsewhere, by far the highest contributions to the photochemical production of CO2 would come from lakes located between 30°N and 60°N latitude. In particular, of the ~7 × 104 lakes we selected for the study, around 50 % of CO2 photogeneration would be accounted for by just 7 large lakes, of which only one is located in the tropical belt. It appears that the lake surface is a very important factor that affects the overall photomineralisation potential of dissolved organic matter.