Impact of hydrophyte decomposition on the changes and characteristics of dissolved organic matter in lake water

Hydrophyte decomposition can generate a large amount of decomposed organic matter that results in potential risks to water quality. Dissolved organic matter (DOM) collected from lake water induced by hydrophyte decomposition may play a key role in understanding the change in the water quality. Spectroscopic techniques can reveal the spectral properties of DOM and their impact on the water quality under oligotrophic and eutrophic growth conditions, such as the application of ultraviolet visible (UVvis) spectra and fluorescence spectroscopy in combination with parallel factor analysis (PARAFAC) method. The results indicated that dissolved organic carbon (DOC), a(350), and UV absorption in a unit of TOC at 254 nm (SUVA254) values under eutrophic growth conditions in summer are generally higher than those under oligotrophic conditions in winter. Five fluorescent components, including one humic-like substance (C4), one fulvic-like material (C3) and three protein-like materials (C1, C2 and C5) were obtained by PARAFAC analysis from hydrophyte-derived DOM samples under different growth conditions and in different seasons. The Fmax of the different fluorescent components were greatly influenced by hydrophyte decomposition, and varied under these different conditions. The results of water quality parameters also showed that dissolved oxygen (DO), chemical oxygen demand (COD), total phosphorus (TP), and total nitrogen (TN) concentrations for oligotrophic and eutrophic conditions in the summer (OS and ES) samples were generally higher than those in the winter samples. The characterization of hydrophyte decomposition DOM is of great importance in eutrophic lake management. Thus, much effort should be put into the study of hydrophyte-derived DOM characteristics and their potential risks as a carrier of hazardous pollutants. The study provides scientific guidance for lake clean water management.