Based on the measured water quality data of national control stations in Changsha city of Xiangjiang River from 2016 to 2019, the principal component analysis method was used to evaluate the water quality at each section. The annual trends in concentrations of ammonia nitrogen and total phosphorus were analysed and the influencing factors were explored. The results show that the water quality of the tributaries of the Xiangjiang River was worse than that of the main stream. The average score of the principal component of Shengli section is the highest, which is 4.412. This suggests that the water quality is poor, where the main pollution sources are domestic sewage and agricultural discharge. From 2016 to 2019, the concentrations of ammonia nitrogen and total phosphorus in each tributary showed a downward trend. The variations of the water quality in each year were mainly affected by rainfall, e.g., the water quality concentration in the dry season was higher than that in the flood season.

Changsha is a highly industrialized city in Hunan Province, China, where the water quality is of great importance to the development of economy and environment in this area. We have analyzed the characteristics of ammonia nitrogen in the Xiang River in Changsha from 2016 to 2019. The results showed that in the main stem, concentrations of ammonia nitrogen were very low and reached the third water quality level. In the six tributaries, concentrations of ammonia nitrogen have increased, especially in Longwanggang and Liuyang River, where the latter of which has a large number of industries and domestic sewage. Correlations between monthly precipitation and ammonia nitrogen concentrations were negative, besides two sites Jinjiang and Juzizhou, indicating that in most rivers, ammonia nitrogen contents had been diluted by rainfall. In general, concentrations and fluxes of ammonia nitrogen have decreased significantly during this time period, suggesting that water environment has improved greatly under the series of the clean motions by the local government.

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