Abstract: In line with the finite discrete benchmark values specified in the China 2020 Water Quality Criteria for Freshwater Aquatic Organisms:Ammonia Nitrogen issued by China's Ministry of Ecology and Environment, we quantitatively assessed the ecological risk (RQ) associated with ammonia nitrogen to aquatic organisms at six key measurement stations within Poyang Lake in 2018. We further elaborated the influences of temperature and pH levels on the toxicity of ammonia nitrogen to aquatic organisms, and advocated for the application of the China 2020 Water Quality Criteria for Freshwater Aquatic Organisms:Ammonia Nitrogen. This offers a much-need empirical reference and quantitative database for effectively managing ammonia nitrogen levels within Poyang Lake. The findings reveal several trends: the most elevated average concentration of ammonia nitrogen arises during the winter months while the lowest happens in the fall; both the short-term water quality benchmarks (SWQC) and long-term water quality benchmark (LWQC) in summer are the least, whereas the spring records the highest. Noting an LRQ>1 in representative summer months for Poyang Lake indicates that the ongoing ecological risk posed by ammonia nitrogen surpasses environmental tolerance levels in that period. Furthermore, raised water temperature and pH levels contribute to a decrease in summer SWQC and LWQC, hence escalating the ecological risk. As such, pH value monitoring and early warning should serve as a prime focus of water resource management strategies for Poyang Lake.

Key words: water environment, ammonia nitrogen, aquatic organism, water quality criteria, ecological risk, Poyang Lake