This study discusses several key biogeochemical functions and their possible consequences due to organic matter pollution and global warming.The contents of dissolved organic matter (DOM) studied in various lakes demonstrate that the autochthonous DOM in lake epilimnion significantly increased,approximately 19-88％,during the summer stratification period.The two fluorescent components are remarkably identified in lakes with high contents of DOM using a parallel factor (PARAFAC) analysis on sample(s) excitation -emission matrix (EEM) spectra,but they are not detected in lakes with low contents of DOM.The experimental results show that the fluorescent DOM (FDOM) is autochthonously originated from both photochemical and microbial assimilations of algal biomass.This study has been applied a new tool,the fluorescence index ( Findex),to distinguish the autochthonous fluorescent components from allochthonous fulvic acid as well as to understand the changes in the fluorophores of fulvic acid caused by photochemical and microbial functions in lake ecosystem.Photodegradation causes the decrease in fluorescence at epilimnion than hypolimnion in lake ecosystem.Correspondingly,photodegradation produces the several photoproducts such as photobleached fulvie acid,low molecular weight (LMW) DOM,dissolved organic carbon (DIC),NH4 +,PO43-,hydrogen peroxide ( H2O2),organic peroxides ( ROOH),and so on.But the photoproducts are largely produced in lakes having high contents of DOM and thus enhance the photosynthesis,thereby enhancing the high production of algal biomass in lake ecosystem.The evidences demonstrate that algal biomass releases the autochthonous DOM,PO43- and NH4 +,as well as regeneration of nutrients ( NO3 - and NO2- ) occurred during this processes,which severely deteriorate the water quality in lakes.Concurrently,these components are photochemieally active to undergo further photodegradation that leads to prolongation of photosynthesis in lake ecosystem.Due to global warming,an increase in water temperature affects to enhance the photodegradation ofDOM that subsequently corresponds to further enhance the photosynthesis.This effect generates the oscillations and chaos in the lake chlorophyll a maxima,which causes to changes in biogeochemical functions in the entire lake ecosystem.A conceptual model of the photodegradation of DOM and their subsequent changes in biogeochemical functions suggests that any changes in nature are absolutely linked with other changes in natural ecosystem.