The DMM percentage that could be transformed by dark OH can be obtained by comparison between the dark and photochemical processes, by using the photochemical t1/2DMM, the role of OH in DMM transformation (from which one gets the first-order rate constant of DMM transformation by OH alone, kDMM−O•H) and the epilimnion irradiation time needed to produce the same total formed OH as in the dark. This approach holds under the Potassium Canrenoate that natural water components (mostly organic and inorganic carbon) scavenge OH to the same extent in both dark and irradiated compartments. Table 1 shows that differences in the relevant parameters between epilimnion and hypolimnion water were not substantial for AV and VI, but water from the lake surface had higher pH than that in the bottom. This issue implies a higher concentration of carbonate in the epilimnion that could induce a more efficient scavenging of OH ( Al Housari et al., 2010). Considering that oxygenation of anoxic hypolimnion water would imply some mixing, leading to intermediate chemical composition, here it is hypothesised for simplicity that the OH scavenging is the same for both the dark and the photochemical processes. This approximation might induce an underestimation of the importance of the dark process.