Abstract: Chlorophyll a (Chl-a) concentration is a key indicator for assessing the status of aquatic ecosystems,and it is influenced by a variety of environmental factors,including water quality,meteorological conditions,and hydrological parameters.To investigate the effects of different environmental factors on Chl-a concentration in Hedi Reservoir,this study conducted monthly surveys over a one-year period at various locations,including the upstream and downstream river mouths,the reservoir center,and the water intake.The results showed significant spatiotemporal variations in Chl-a concentration in Hedi Reservoir.Temporally,Chl-a concentration followed the order:summer > spring > autumn > winter,and spatially,it followed the order:river mouth > reservoir center > water intake,with the upstream region displaying higher concentrations than the downstream area.Pearson correlation analysis and univariate analysis showed that three meteorological factors (water temperature,shortwave solar radiation,and wind speed),two hydrological factors (outflow and water depth),and three water quality factors (nitrite nitrogen,total phosphorus,and transparency) were statistically significant (P<0.05) with variance explanation rates exceeding 10%.Multivariate Generalized Additive Model (GAM) analysis demonstrated that environmental factors collectively explained 82.7% of the variation in Chl-a concentration.The significance hierarchy of environmental factor impacts was ranked in descending order as meteorological factors > hydrological factors > water quality factors.Variance partitioning analysis revealed that the explanatory rates of these factors followed the order meteorological factors > water quality factors > hydrological factors.Therefore,this study recommends that,in addition to considering the contributions of water quality factors,greater emphasis should be placed on investigating the impacts of meteorological and hydrological factors on Chl-a concentration in Hedi Reservoir.