Water Quality in Representative Tuojiang River Network in Southwest China

To control pollutants in rivers, we need to have an understanding of the spatial and temporal variations on water quality in complex river networks. In this study, 153 sampling sties were located in Chengdu segment of Tuojiang River in 2017, 23 monitoring stations in Tuojiang River in the Chengdu segment from 2011 to 2016 were also collected. According to the data from the monitoring station, the concentrations of total nitrogen (TN), total phosphorus (TP), ammonia nitrogen (NH4+), and chemical oxygen demand (CODcr) concentrations were exceeded the water quality targets at 22, 14, 10, and 3 of the 23 monitoring stations, respectively. The regression analysis showed the NH3, TN and TP was increased from 2011 to 2016 (R-NH4+(2) = 0.30, p < 0.05; R-TN(2) = 0.88, p < 0.05; R-TP(2) = 0.30, p < 0.05), which indicated water quality was deteriorated from 2011 to 2016. In the 153 sample sites, the NH4+, CODcr, TP and TN concentrations exceeded the class III water quality threshold at 23%, 23%, 26%, and 99% of the total sampling sites, respectively. Correlation analysis showed that the main sources of NH4+, CODcr, TN, and TP (R-NH4+-CODcr(2) = 0.572; R-NH4+-TN(2) = 0.543; R-NH4+-TP(2) = 0.537, p < 0.01 were municipal domestic sewage. The main pollutants in Tuojiang river network were TN and TP, high P and N concentrations probably contribute to the deterioration of surface water quality at some sampling sites (R-TPs-TP(2) = 0.183 and R-TNs-NH4+(2) = 0.472, p < 0.01). TP, TN, TP in the sediments (TPs), and TN in the sediments (TNs) have accumulated in the river system because the river morphology has been changed by, for example, the damage of riparian zones and the construction of water conservation structures. The results from this study will support initiatives to improve the overall water quality and function of the river ecosystem.