Water quality criteria of total ammonia nitrogen (TAN) and un-ionized ammonia (NH3-N) and their ecological risk in the Liao River, China

Ammonia has drawn great concern worldwide due to its ubiquity in surface water and high toxic effect. In China, ammonia pollution issues in the Liao River were highlighted from the Ministry of Ecology and Environment annual report. In this study, water quality criteria (WQC) for two types of ammonia (total ammonia nitrogen (TAN) and un-ionized ammonia (NH3-N)) and related temporal concentration distributions and ecological risks in the Liao River were investigated. For sampling sites (2014) and national monitoring sites (2008, 2013, 2016, 2017 and 2018) of the Liao River, there were seasonal variations identified for TAN and NH3-N. More specifically, high concentrations of TAN and NH3-N occurred separately in winter and summer, and there were increasing trends for TAN and NH3-N from 2013 to 2018. The acute and chronic WQC values for TAN based on the toxicity values of the Liao River species were 16.86 and 4.39 mg/L (pH of 7.0 and temperature of 20 °C), and the acute and chronic WQC values for NH3-N were 0.067 and 0.017 mg/L. The exceedance probabilities of 5% species affected for long-term exposure of TAN and NH3-N were ≥30% in 2014. In addition, the increasing trend of concentrations and ecological risks posed by NH3-N from 2013 should be paying more attention. This study could provide useful information for ammonia environmental risk management in China and ecological risk assessment procedure for NH3-N and TAN exposure in similar surface waters worldwide.