Study on Water Quality and Trophic Status of Subtropical Cascade Reservoirs in Dongjiang River Basin in Dry Season

VAST Institute of Water Ecology and Environment, Shenzhen 518101, China

^* Corresponding author: Songyunlongwater@163.com

Abstract

The Dongjiang River Basin is an important water source for Guangdong Province, providing water for living, production and ecology for more than 40 million people. The three large reservoirs, Xinfengjiang Reservoir, Fengshuba Reservoir and Baipenzhu Reservoir, are the three largest reservoirs in the Dongjiang River Basin. The quality of the water environment in the three reservoirs plays an important role in ensuring the safety of drinking water and promoting the overall protection, systematic restoration and comprehensive management of the water ecosystem. 11 indicators, including water temperature, transparency, pH, DO, turbidity, conductivity, ammonia nitrogen, TN, TP, COD_Mn and chlorophyll a, were tested in October 2022 to study the water quality characteristics and trophic status of the three cascade reservoirs. The results of the single-factor evaluation of water quality showed that all three reservoirs reached the surface water class II level. TN is the primary pollutant in Fengshuba and Baipenzhu reservoirs. The concentration of Chla in Baekpongju Reservoir was 3.4 μg/L, with a mild risk of algal bloom. TLI (Σ) of the three cascade reservoirs were about 16.41~32.14.The results of the integrated nutrient status evaluation showed that Xinfengjiang Reservoir was in a depleted nutrient status, while Mapeshuba and Bailuanzhu Reservoirs were in a medium nutrient status. Factor analysis showed that 11 water quality factors can be classified into four categories. F1 represents the organic pollution. F2represents the phytoplankton biomass. F3 represents the concentration of nitrogen. F4 represents the suspended solids in water.