Abstract: The widespread use of chlorine-containing disinfectants inevitably leads to chlorine pollution as residues enter natural water bodies through rainfall runoff. To investigate the temporal and spatial distribution of chlorine in lakes, a hydrodynamic-water quality model of Nanhu Lake was established using the Infoworks ICM simulation platform. The model was used to analyze the temporal and spatial variation of chlorine concentration in Nanhu Lake under different chlorine discharge cycles and rainfall conditions. The results indicated that: 1) During a single discharge, a high concentration zone of chlorine was initially formed in the nearshore water body. The chlorine diffused from the lakeshore to the lake center, where the concentration decreased. At the end of chlorine discharge, the concentration reached a peak value of 1.25 mg/L and gradually decreased, with chlorine concentration attenuating from the water center towards the boundary. This process lasted approximately 14 hours. 2) The influence of periodic inflow is mainly reflected in the decrease of chlorine decay rate in the new cycle. The decay duration increased, and the peak value of chlorine concentration also increased. The peak values of chlorine concentration in three cycles were 1.25 mg/L, 1.58 mg/L, and 1.89 mg/L, respectively, with decay durations being 14 hours, 15.7 hours, and 17.1 hours, respectively. 3) Under the influence of rainfall, the range and depth of chlorine pollution expanded towards the lake center, and the pollution duration increased to approximately 20 hours. The peak concentration of chlorine also increased, reaching up to 7 mg/L.

Key words: water environment, residual chlorine, spatial and temporal distribution, chlorine-containing disinfectant, Infoworks ICM, Nanhu Lake