Assessing the Spatiotemporal Dynamics of Algal Communities in Urban Reservoirs: Influence of Reservoir Characteristics and River-reservoir Connectivity

Algae in the lake-reservoir system of Guangdong, Hong Kong and Macao Greater Bay Area have important impacts in the regional water supply, but their dynamic characteristics and driving mechanisms have not been clarified. In this study, we systematically analyzed the influence mechanisms of water quality and hydrodynamic factors on algal proliferation in four interconnected reservoirs in Zhuhai City through continuous monitoring data from 2019-2022. The study first revealed the evolution of environmental parameters and algal communities based on seasonal scales: the analysis of 10 water quality and hydrodynamic indicators revealed that the hydrological conditions in the rainy season were more favorable to algal proliferation, and the four reservoirs showed differential community succession paths and spatial and temporal differences in diversity. In order to further analyze the causes of algal differences among lakes, this paper used principal component analysis (PCA), Mantel's test and NMDS methods to clarify that river-reservoir connectivity was the main driving factor affecting them. For the period of no river-reservoir connectivity, ammonia nitrogen and permanganate index (IMn) were the core environmental factors driving the changes of algal communities, and their mechanisms of action were mainly realized by influencing chlorophyll concentration. For the period of river-reservoir connectivity, hydraulic residence time (HRT) and discharge had a significant regulatory effect on algal biomass, and its mechanism of action was mainly through regulating the efficiency of algal nutrient uptake. This study reveals the key driving elements of algal dynamics in lakes and reservoirs in the Guangdong-Hong Kong-Macao Greater Bay Area, and provides a scientific basis for the ecological safety management of cross-regional water transfer systems. • Strong river-reservoir connectivity raises algal diversity over weak connectivity. • Wet-season nutrient surges (Apr–Sep) raise algal density but suppress diversity. • NMDS unveils distinct algal assemblages, clarifying reservoir ecological shifts. • Shorter HRT, controlled outflow, and higher levels cut nutrients and curb blooms.