Photolysis is measured with the help of a spectrophotometer, by examining
the decrease of a320 over time as sunlight is having its effect.
Water samples taken in a pond in July 2007 were filtered to remove microorganisms and thus observe only the effect
of light. Then these samples were exposed to light or darkness (controlled conditions) before their examination with
the spectrophotometer. The results demonstrate how the breakdown of organic molecules by light is expressed by a decrease
of water colour. It would seem that part of the molecules that give to water its colour are transformed into CO2,
thus contributing to the production of greenhouse gaz. This fraction remains unknown. Other than CO2, photo-products can be smaller
organic molecules, which microorganisms can use more easily (increasingly labile molecules). Thus, one indirect effect of
dissolved organic carbon photolysis is to stimulate microbial activity, which in turn frees up carbon by respiration.