Dissolved organic matter (DOM) is one of the largest reduced carbon pool in aquatic environments. The transformation of  labile organic matter to either CO2 or recalcitrant DOM determines the carbon source or sink issues of aquatic carbon cycle. Till now, most studies on DOM focused on surface systems which are regulated by multiple complex factors. In this talk, I will compare DOM turnover from the dark margial basins (South China Sea, etc) to hypolimnetic dam reservoirs/lakes where deoxygenation deminates  OM trnsformations.