Applying zooplanktonic biological indices for assessment of water quality in the watersheds of Ray river, Baria-Vung Tau province

The Ray River is an important river system in Ba Ria-Vung Tau Province, Vietnam, supplying water for domestic, agricultural, and industrial purposes, thereby facilitating the province's economic development. The research was executed in 2024 across 9 watersheds, comprising 5 sites on the Ray River and 4 sites on the Ray River reservoir, throughout both the rainy and dry seasons. The findings documented 111 species of zooplankton, categorized into 50 genera, 13 orders, and 5 primary groups: Protozoa, Rotatoria, Cladocera, Copepoda, and Ostracoda. The research noted variations in zooplankton communities throughout the two seasons, suggesting saline intrusion at specific locations along the Ray River during the dry season. The Shannon-Wiener biodiversity score varied between 1.95 and 3.43, whereas the Pielou Evenness index consistently exceeded 0.8. The biological indicators of zooplankton communities indicate that most aquatic systems exhibited generally clean water quality, with only two locations demonstrating moderate pollution levels (α-mesosaprobe) during the dry season. The findings indicate that the aquatic environment in the Ray River system, encompassing both the river and reservoir, satisfies the water supply criteria for supplying domestic water and irrigation water in Ba Ria-Vung Tau Province. The study suggests utilizing zooplankton as an indicator for precise water quality scenarios, owing to their sensitivity to environmental fluctuations and brief life cycles. This would also offer a cost-effective approach for environmental monitoring and management of the river system.