The response of phytoplankton community to dissolved organic matter composition and lake trophic state: Insights from the largest urban lake in China

The dual impacts of human activities and climate change have increased the input of dissolved organic matters (DOM) into urban lakes, which is crucial for aquatic biogeochemical cycle and global carbon cycle, affecting the lake ecological health to some extent. What's more, phytoplankton are sensitive to changes in water environment, making them important indicator organisms in water environment monitoring. However, the composition dynamics of phytoplankton community and DOM in shallow urban lakes under strong anthropogenic disturbances, and their relationship remain poorly understood. Thus, this study aimed to reveal the composition dynamics of phytoplankton community and DOM in urban lakes, identify the main environmental factors affecting phytoplankton communities, and understand the relationship between DOM and phytoplankton composition in various trophic states. A whole-year campaign was conducted in Tangxun Lake, Wuhan City, the largest urban lake in China, which is highly urbanized and industrialized. The parallel factor analysis method (PARAFAC) was applied to identify the three-dimensional fluorescence spectra and components of DOM. As a result, it was found that: The water quality of Tangxun Lake exhibited strong spatiotemporal variability, mainly presenting a state of eutrophication to moderate eutrophication. A total of 54 genera, 26 families, 15 orders, 9 classes, 6 phyla of phytoplankton have been identified in Tangxun Lake. The phytoplankton community structure was diatomic-green algae-cyanobacteria type as a whole, and the seasonal succession changes of phytoplankton community were significant. Excitation–emission matrix fluorescence spectroscopy (EEMs) coupled with PARAFAC indicated that DOM in Tangxun Lake consisted of four components, mainly terrestrial component. This study reveals the response of phytoplankton to DOM and lake trophic status, which has profound implications for the aquatic ecosystem management, and provide reference for the potential correlation mechanism among lake carbon cycle, CDOM source composition and phytoplankton community.