Long-Term Changes in Water Quality and Eutrophication of China’s Liujiang River

Long-term changes (2003-14) of water temperature, DO, pH, TN, NH4-N, TP, and COD Mn were examined at eight sampling stations along the Liujiang River. Water quality parameters showed considerable spatial and temporal variability. Annual averages of those parameters were 22.1 degrees C, 7.8 mg/L, 7.58, 1.35 mg/L, 0.27 mg/L, 0.06 mg/L, and 1.7 mg/L, respectively. An increasing trend for TN/TP and a decreasing trend for pH were observed in all parts of the Liujiang. Pollution levels were generally higher in the lower Liujiang than in the upper and middle parts of the river due to the impact of urban sewage. All indicators reached level III water quality standards except TN, which suggests that the control of nitrogen emissions should be strengthened. Relatively high N/P ratios in the Liujiang contribute to a potential for phosphorus limitation of phytoplankton. The average concentration of Chlorophyll-a was 1.2 mu g/L in 2014. The TLI index indicated that the eutrophication state of the Liujiang was mesotrophic, while the downstream water was polluted due to its nutrient inputs from agriculture and urban sources. The water quality of the river keeps well by comparison to other major rivers of the world, which provided the basis for urban development and river protection in Liuzhou City.