Modaomen Waterway is the main outlet of the Pear River system and an important water source for Zhuhai and Macao. The water quality of 13 sampling sites in Modaomen Waterway, phytoplankton, and environmental factors were investigated at 21 sampling sites in 4 drinking water source groups, which transport water from Modaomen Waterway and connect with each other, in August and October of 2021. A total of 73 genera of phytoplankton in eight phyla were identified, with a total of 150 species, most of them belonging to Cyanophyta, Chlorophyta, and Bacillariophyta. The relative abundance of Cyanophyta was higher than 90% in the DJS and YL reservoirs during flood and dry seasons; Cyanophyta, Chlorophyta, and Bacillariophyta were dominant phyla during different seasons; and their distribution was balanced in the ZXD and ZY reservoirs. The Shannon-Wiener index, Pielous uniformity index, and Margalef richness index showed that the ZY reservoir had the most abundant biodiversity, which indicated the best water quality, followed by the ZXD and YL reservoirs. Conversely, the DJS was the least diverse reservoir for phytoplankton. The PCoA analysis indicated significant differences in plankton structures in ZXD and ZY with the other two reservoirs (P<0.05), respectively. Redundancy analysis (RDA) showed that the main environmental factors affecting the distribution of the phytoplankton community were NO3-, TOC, TP, Cl-, and NH4+-N. These results indicated that the phytoplankton community of the four reservoirs were greatly affected by the nutrient salt caused by water transport, which suggested that the water quality of Modaomen Waterway should be improved to increase reservoir water nutrition to ensure the safety of drinking water sources.
Keywords: Modaomen Waterway; drinking water reservoirs; environmental factors; phytoplankton; redundancy analysis (RDA).