Fluorescence Characteristics of DOM in Overlying Water of Erhai Lake and Its Indication of Eutrophication

The composition characteristics of dissolved organic matter (DOM) have an important effect on water quality. The study on the composition characteristics of DOM in overlying water is the great significance to the indication of the lake eutrophication status. The temporal and spatial changes of DOM components in overlying water of Erhai Lake, and the relationship between DOM components and water quality factors were quantitatively analyzed by fluorescence spectroscopy regional volume integral analysis (FRI). The fluorescence characteristics of DOM components in the different source water bodies and different eutrophication levels of plateau lakes were compared and analyzed. The results showed that humic acid was the main type of DOM in overlying water of Erhai Lake, followed by fulvic acid. The contents of DOM and humic acid were higher in the middle of Erhai Lake. Tryptophan and tyrosine and other protein-like DOM were higher in the south, and a higher level of the fulvic acid DOM was in the north. During the Algal Bloom (in October), the protein DOM and the fulvic acid DOM were lower and the humic acid DOM significantly increased, and biological source DOM and biological activity of DOM decreased. The endogenous release of sediments in the Erhai Lake and its inflow rivers mainly affected the humic acid DOM in overlying water, and then the wet deposition mainly increased the protein-like DOM. During the poor nutrition stage, the fulvic acid DOM had greater impact on water quality, and in the eutrophic stage, the humic acid DOM had a great influence on water quality. Following the increase of the lake eutrophication, the proportion of the protein-like DOM and fulvic acid DOM decreased in overlying water, and then the proportion of microbial degradation products and the humic acid DOM showed an increasing trend. The proportion change of fluorescent components in DOM had an indication of the lake.