Hydrological dynamics regulate reactive oxygen species production in the largest freshwater lake of China.

Photochemically generated reactive oxygen species (ROS) are ubiquitous in aquatic ecosystems and play a key role in pollutant attenuation. ROS production is mediated by abiotic/biotic pathways, yet the influence of hydrological dynamics on these processes and ROS production remains poorly understood. Herein, we conducted a one-year investigation of ROS production in Poyang Lake across the spring rising, summer flood, autumn retreating, and winter dry periods. Results showed that the concentrations of triplet-excited state of dissolved organic matter (3DOM*) and singlet oxygen (1O2) consistently increased from spring to autumn before declining in winter, whereas those of hydroxyl radical (•OH) peaked in summer. The presence of microorganisms provided biotic contributions to ROS production, with higher proportions in summer and autumn. These variations were regulated by the dual impacts of hydrological dynamics on DOM characteristics and microbial communities. Specifically, hydrologically driven DOM with higher DOC concentration, E2/E3 ratios and humification index (HIX) enhanced ROS production during flood and retreating periods, while Cyanobacteria and Proteobacteria were statistically significantly correlated with DOM characteristics and ROS production. Random forest and partial least-squares path modeling analyses further revealed that DOM characteristics directly dominated ROS generation, whereas microbial communities exerted indirect effects via modifying DOM characteristics. These findings systematically elucidated the underlying mechanisms by which hydrological dynamics regulate ROS production, contributing to a better understanding of organic pollutants degradation and biogeochemical cycling under global climate change.