Composition, structural characteristics and indication of water quality of dissolved organic matter in Dongting Lake sediments

•Abundant humic-like substances maintain the good water quality.•High humification degree and the substitution groups with few aliphatic chains.•P(III+V,n)/P(I+II,n) was taken as an indicator for the change of the water quality.•Changes of composition and structure of DOM can establish a relationship with water quality, and will have an indicative effect on lake trophic status.

This study aims to establish the relationship between the composition, structure of sediment dissolved organic matter (DOM) and water quality based on changes of environmental conditions in Dongting Lake. Hence, UV–vis absorbance and fluorescence spectroscopy were combined to characterize the components and structure of DOM in surface sediments of Dongting Lake. The relationship of the structural characteristics of DOM with N, P contents and water quality was also explored. The results showed that the DOC contents of Dongting Lake sediments were between 60.004 and 368.286 mg kg−1, with the general trend of Eastern > Southern > Western for the Dongting Lake regions. The DOM in the sediments mainly comprised humic-like substances, which were greater in the Eastern than in the Southern and Western Dongting Lake regions by 4.1% and 6.43%, respectively. The humification degree of DOM in the sediments was high, and the substitution groups in the aromatic rings mainly contained carbonyl, carboxyl, hydroxyl, and esters. The source of DOM in the Dongting Lake sediments was significantly influenced by terrestrial input and biological metabolism. Furthermore, the composition and structural characteristics of DOM in the Dongting Lake sediments were found to be closely related to the contents of N and P in the sediments, as well as the water quality. Especially, the ratio of humic-like substances to protein-like substances (P(III+V,n)/P(I+II,n)) can be indirectly taken as an indicator of water quality. Thus, the changes of composition and structure of sediment DOM can establish a relationship with the water quality, and will have an indicative effect on lake trophic status.

Graphical abstractThe composition and structure characteristics of DOM in Dongting Lake sediments were found to be closely related with the content of N, P in sediments and the water quality, thus the contents of N and P forms in water, sediment and the concentration of Chl-a, DO, CODMn in water might increase when the composition and structure of sediment DOM, especially, DOC content, protein-like substances, humic-like substances, substitution groups in the aromatic rings, the ratio of humic-like substances to protein-like substances continuously change under certain conditions (such as ionic strength, pH, redox potential, heavy metals, microbial degradation, terrestrial pollutant, etc.). Moreover, these would affect the water quality and lake trophic status.Figure optionsDownload full-size imageDownload as PowerPoint slide